CA1105693A - Non-aqueous acid emulsion composition and method for acid-treating siliceous geological formations - Google Patents
Non-aqueous acid emulsion composition and method for acid-treating siliceous geological formationsInfo
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Abstract
"ABSTRACT OF THE DISCLOSURE"
A stable, non-aqueous acid emulsion composition com-prising an admixture of a substantially anhydrous polyphos-phoric acid-based mixture, an organic solvent, and a surfactant;
and a method for increasing the permeability of siliceous sub-terranean geological formations.
A stable, non-aqueous acid emulsion composition com-prising an admixture of a substantially anhydrous polyphos-phoric acid-based mixture, an organic solvent, and a surfactant;
and a method for increasing the permeability of siliceous sub-terranean geological formations.
Description
~ ~$~
The invention relates to the acicl treatment of subterranean earth formations, and more particularly to the acid treatment of siliceous subterranean formations surround-ing oil wells, gas wells, water injection wells and similar boreholes.
~ cid treatment or "acidizing" is a well-known expedient employed for rejuvenating oil-producing and gas-producing formations and to facilitate the ease with which fluid such as water, brine or yas can be injected into sub-1~ terranean formations surrounding a wellbore. Acidizing ofsiliceous formations, e.g. sandstone, shale, serpentines, etc., has met with some favorable results when the formation is treated with hydrogen fluoride. Various modifications of this hydrogen fluoride acidizing have been disclosed in the prior art. These modifications have mainly consisted of the use of various mixtures of h~drogen fluoride and various other mineral acids such as orthophosphoric acid, fluorophosphoric acid, sulfuric acid, hydrochloric acid, etc. Although such mixtures are generally effective, experience has shown that many forma-tions do not respond to the acid treatment.
In general, hydrocarbon-bearing siliceous formations are of a heterogeneous nature and contain a variety of inor-ganic materials. In addition the pores of the formation may contain objectional deposits of organic matter such as viscous crude oil, waxes, asphaltenes and resin precipitates of petro-leum origin. Conventionally, before the acidizing treatment is begun this undesirable organic matter must be removed. Solvents such as carbon disulfide, carbon tetrachloride, or an aromatic hydrocarbon are first injected into the formation surrounding the well. This solvent treatment is repeated several t:imes .~
~ .
until the pores of the formation are relatively free of the organic material to insure a proper acidizing environment in the formation.
Another problem common to all methods of acidizing is the production of precipitates within the formation interstices through the action of the acid-treating reagent or its byproducts on some precipitate-forming constituent of the formation. This generally occurs when the acidizing fluid is spent and precipitates in a form which plugs the pores of the producing formation. As noted above, acidizing techniques have previously employed mixtures of phosphoric acid, generally referred to as orkhophosphoric acid, with other mineral acids.
~owever, the orthophosphates of pol~valent or heavy metals are all virtually insoluble in water. For example, calcium and magnesium compounds are found in all producing formations, and when attacked by phosphoric acid mixtures form insoluble phos-phates. The calcium and magnesium phosphates are especially .
difficult to remove and re~uire expensive procedures to revita-lize a producing formation. Therefore, there exists a need for a composition which will provide a "one shot" acidizing treatment which removes objectionable deposits of organic material, eliminating the need for a separate solvent treatment step, along with an acidic-treating reagent that does not form precipitates within the formation.
Accordingly, a principal object of this invention `
is to provide a novel composition and method for increasing the permeability of siliceous subterranean formations.
Another object is to provide a composition and method which remove both acid-soluble and oil-soluble compo-nents from the formation.
A further object is to provide a composition whlch does not form undesirable precipitates on reac-tion with the formation.
Other objects, advantages and ~eatures of the inven-tion will become apparent ~rom the following description and appended claims.
This invention provides a substantially anhydrous emulsion comprising (1) about 5 to 95 parts by weight of an acid component comprising (a) about 50 to 99 parts by weight of polyphosphoric acid having about S to 86 weight percent of the total P2O5 present as polymeric P2O5, (b) about 1 to 25 parts by weight of hydrofluoric acid, and (c) 0 to about 50 parts by weight of a catalyst selected from ~he group consis-ting of (A) strong mineral acids selected from the group con-sisting of sulfuric, nitric, perchloric and hydrochloric acids and mixtures thereof; (b) carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C) oxidizing agents selected from the group consisting of hydro-gen peroxide, potassium chromate, potassium permanganate and chromic acid; (2) about 5 to 95 parts by weight of an organic solvent component; (3) about 0.01 to 3.0 parts by weight of an anionic or nonionic surfactant component; and wherein -the H2O/P2O5 mole ratio of the overall emulsion is less than 3.4.
An em~odiment of the invention provides a substan-tially anhydrous emulsion comprising: (1) about 25 to 75 parts by weight of an acid component comprising (a) about 60 to 95 parts by weight of polyphosphoric acid having about ~0 to 75 weight percent of the total P2O5 present as polymeric P~O5, ~,~, I
(b) about 2 to 8 parts by weight of hydrofluoric acid and (c) about 2 to 40 parts by weight of a catalyst selected from the group consisting of (A~ strong mineral acids selected from the group consisting of sulfuric, nitric, perchloric and hydrochloric acids and mixtures thereof; (B~ carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C) oxidi-zing agents selected from the group consisting of hydrogen peroxide, potassium chromate, potassium permanganate and chromic acid; (2) about 25 to 75 parts by weight of an organic solvent composition comprising (a) about 40 to 65 parts by weight of a normally li~uid aliphatic hydrocarbon distillate boiling in the range of about 120~ to 550 F., (b) about 10 to 30 parts by weight of a normally liquid aromatic hydrocarbon, (c) about 1 to 5 parts by weight of an ether of an aliphatic alcohol, and (d) about 2 to 10 parts by weight of a lower alkyl monohydric alco-hol; (3) about 0.1 to 1.0 parts by weight of an anionic or nonionic surfactant component; and wherein the H2O/P2O5 mole ratio of the overall emulsion is between 2.2 and 2.8.
This invention further provides the method for in-creasing the permeability of a siliceous subterranean geological formation penetrated by a well which comprises lntroducing --through said well and into the formation surrounding said well a substantially anhydrous emulsion comprising: (1) about 5 to 95 parts by weight of an acid component comprising (a) about 50 to 99 parts by weight polyphosphoric acid, said polyphosphoric acid containiny about 5 to 86 weight percent of the total P2O5 present as polymeric P2O5, (b~ about 1 to 25 par~s by weight of hydro-fluoric acid, and (c) 0 to about 50 parts by weight of a catalyst selected from the group consisting of (A~ strong mineral acids selected from the group consisting of sulfuric, nitric, per-chloric and hydrochloric acids and mi~tures thereof; (~) , -4-organic carboxylic acids selected from the group consisting of formic, acetic, chloroacetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C~ oxidizing agents selected ~rom the group consisting of hydrogen peroxide, potassium chromateg potassium permanganate and chromic acid; (2) about 5 to 95 parts by weight of an organic solvent compo:nent; (3) about 0.01 to 3.0 parts by weight of an anionic or nonionic surfac-tant; and in which the ~I2O/P2O5 mo:Le ratio is less than 3.4 in the overall acid emulsion.
A further embodiment of the invention provides a siliceous subterranean geological formation penetrated by a well bore which comprises introducing into the formation a highly viscous, substantially anhydrous, liquid-acid-mixture composi-tion, comprising: (1) about 25 to 75 parts by weight of an acid component comprising (a) about 60 to 95 parts by weight polyphos-phoric acid, said polyphosphoric acid containing abou-t 40 to 75 weight percent of the total P2O5 present as polymeric P2O5, (b) about 2 to 8 parts by weight of hydrofluoric acid, and (c) about 2 to 40 parts by weight of a catalyst selected from the group consisting of (A) strong mineral acids selected from the group consisting of sulfuric, nitric, perchloric and hydro-chloric acids and mixtures thereof; (B) organic carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids;
and (C) oxidizing agents selected from the group consisting -of hydrogen peroxide, potassium chromate, potassium permanganate and chromic acid; (2) about 25 to 75 parts by weight of an organic solvent composition comprising (a) about 40 to 65 parts by weight o a normally li~uid aliphatic hydrocarbon distillate boiling in the range o about 120 to 550Q F., (b) about 10 to 30 parts by weight o a normall~ liquid aromatic hydrocarbon, (c) about 1 to 5 parts by weight of an -4a-~5~
ether of an aliphatic polyhydric alcohol, and (~) about 2 to 10 parts by weight of a lower monohydric a].cohol, and (3~ about 0.1 to 1.0 parts by weight o~ an anionic or nonionic surfactant, and in which the ~O~P2O5 mole ratio in the overall emulsion composition is between 2.2 and 2~.
A still further embodiment of the invention provides a method for increasing the permeability of a mixed subterranean geological formation penetrated by a well bore which comprises introducing into the formation a highly viscous, substantially anhydrous, liquid-acid-mixture composition, comprising: (1) about 5 to 75 parts by weight o~ an acid component compxising (a) about 50 to 99 parts by weight polyphosphoric acid, said polyphosphoric acid containing about 5 to 86 weight percent of the total P2O5 present as polymeric P205, (b) about 1 to about 25 parts by ~eight of hydrofluoric acid, and (c) 0 to about 50 parts by weight of a catalyst selected from the group consisting of (A) strong mineral acids selected from the group consisting of sulfuric, nitric, per-chloric and hydrochloric acids and mixtures thereof; (B) organic carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C) oxidizing agents selected from the group consisting of hydrogen peroxide, potassium chromate, potas-sium permanganate and chromic acid; (2) about 25 to 95 parts by weight of an organic solvent component; and (3) about 0.01 to 3.0 parts by weight of an anionic or nonionic suxfactant compo-nent, and wherein the H2O/P2OS mole ratio is from 2.1 to 3.4 in the overall acid emulsion.
A still ~urther embodiment of the invention provides a method for increasing the permeability of a mixed subterranean geological formation penetrated by a well bore which comprises introducing into the formation a highly viscous~ substantially anhydrous, liquid-acid-mixture composition, compxising~
j"~
about 20 to 50 parts by weight of an acid component comprising (a) about 60 to 95 parts by weight pol~phosphoric acid, said polyphosphoric acid containing about 40 to 75 weight percent of the total P2O5 present as polymeric P2O5, (b) about 2 to 8 parts by weight of hydrofluoric acid, and ~c) about 2 to 40 parts by weight of a catalyst selected from the group consisting of (A) strong mineral acids selected from the group consisting of sulfuric, nitric, perchloric and hydrochloric acids and mix-tures thereof; (B) organic carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, tri-chloracetic, citric, oxalic and maleic acids; and (C) o~idizin~
agents selected from the group consisting of hydrogen peroxide, potassium chromate, potassium permanganate and chromic acid; (2) about 50 to 80 parts by weight of an organic solvent composition comprising (a) about 40 to 65 parts by weight of a normally liquid aliphatic hydrocarbon distillate boiling in the range of about 120 to 550~ F., (b) about 10 to 30 parts by weight of a normally liquid aromatic hydrocarbon, (c) about l to 5 parts by weight of an ether of an aliphatic polyhydric alcohol, and (d) about 2 to 10 parts by weight of a lower al~yl monohydric alcohol; and (3) about 0.1 to 1.0 parts by weight of an anionic or nonion.ic surfactant, and which the H2O/P2O5 mole ratio in the overall emulsion composition is between 2.1 and 3.4c The invention relates to a non-a~ueous emulsion composition for increasing the permeability of siliceous subterranean geological formations, and to a method of acidizing which dissolves organic materials and avoids the formation of insoluble inorganic precipitates and many of the other difficul-ties encountered in prior art acidizing methods. The invention 3~ involves the injection into the formation of a novel, non-~. -4c-aqueous emulsion comprising a substantially anhydrous liquid polyphosphoric acid-based mixture, an organic solvent composi-tion, and a surface-active agent or surfactant. The acid com~ .
ponent of the emulsion comprise:s about 5 to 95 parts by weight of a substantially anhydrous liquid polyphosphoric acid-based :;
mixture comprising ~a) about 50 to 99 parts by weight polyphos-phoric acid with about 5 to 86 weight percent of the total P2O5 -present as polymeric P2O5, (b) about 1 to 25 parts by weight hydrofluoric acid, and (c) optionally, 0 to about 50 parts by weight of a catalyst selected from the group consisting of strong mineral acids, carboxylic acids, oxidizing compounds, and mix- ~ -tures thereof, in which the H2O/P2O5 mole ratio in the overall emulsion composition is less than 3.4. The emulsion also contains about 5 to 95 parts by weight of an organic solvent composition selected from the group consisting of polar solvents, hydrocar-bon solvents, and mixtures thereof; and about 0.01 to 3.0 parts by weight of a surfactant selected from the group consisting of anionic surfactants and nonionic surfactants.
This novel, non-aqueous emulsion composition can be utilized in both matrix acidizing and acid fracturing well stimulation pxocedures, and also has utility in many varied applications such as gas drying, extracting metals from ores, metal treatment, removing scale deposits from steam boilers and pipes, and particularly in methods where solvent treatment is desired along wtih acidizing action.
The drawing is a graph illustrating the relationship of the polymeric P2O5 content of the polyphosphoric acid ingre-dient of the emulsion composition as a function of the mole ratiO of H2O/P2O5~
The novel, non-aqueous acid emulsion of the pre.sent invention comprises an acid component, an organic solvent com-ponent and a surfactant capable of forming either an acid-in-solvent emulsion or a solvent-in-acid emulsion. The composition of the non-aqueous polyphosphoric acid-based emulsion employed in carrying out this invention will depend upon its ultimate use.
Compositions of non-aqueous acid emulsions comprising a mixture of about 5 to 95 parts by weight of the acid component; about 5 to 95 parts by weight o~ the organic solvent component; and about 0.01 to 3.0 parts by weight of an anionic or nonionic surfactant are encompassed by the invention.
10The non-aqueous acid emulsion compositions are pre-pared by: (1) adding the surfactant to the solvent component with moderate stirring, and ~2) adding this surfactant-solvent mixture to the acid component with moderate stirring to form the emulsion. The rate of addition of the surfactant-solvent mixture is critical and should be slow enough so as not to break the emulsion already formed. In an alternate method the surfactant is added to the acid component with moderate stir-ring and then the solvent component is blended into this acid ~-mixture. The rate of addition of components must also be con trolled to avoid breaking the emulsion. These methods provide stable emulsions which can be either solvent external-acid internal or acid external-solvent internal. It is generally preferred to use the solvent external-acid internal type emul-sion in treating formations. When this type of emulsion enters a formation pore the solvent first contacts and dissolves any organic material present, thus expo~ing the siliceous formation to the acid.
The general reactions involved in the attack of the substantially anhydrous liquid polyphosphoric-based acid emul-sions of this invention upon siliceous compounds are expressedby the following equation:
4P27 + sio2~ ~0_ -o-p-o~; + 2~1 ~ siF4~ ~P2O7+ ~2 O O
In the first step of the reaction, a phosphosilicate complex is formed. Under anhydrous conditions the soluble phos phosilicate complex then reacts with hydrofluoric acid to pro-duce a gas, silicon tetrafluoride, and to regenerate polyphos-phoric acid and water. The overall concept of this invention ; ?
is that the acid componen-t rapidly dissolves the silica and complexes other metals such as aluminum, iron, cobalt, nickel, copper, zinc, and the like. Polyphosphoric acid mixtures hav-ing a mole ratio of water to phosphorus pentoxide (H2O/P2O5) of between about 2.1 to 3.~, and particularly between about
The invention relates to the acicl treatment of subterranean earth formations, and more particularly to the acid treatment of siliceous subterranean formations surround-ing oil wells, gas wells, water injection wells and similar boreholes.
~ cid treatment or "acidizing" is a well-known expedient employed for rejuvenating oil-producing and gas-producing formations and to facilitate the ease with which fluid such as water, brine or yas can be injected into sub-1~ terranean formations surrounding a wellbore. Acidizing ofsiliceous formations, e.g. sandstone, shale, serpentines, etc., has met with some favorable results when the formation is treated with hydrogen fluoride. Various modifications of this hydrogen fluoride acidizing have been disclosed in the prior art. These modifications have mainly consisted of the use of various mixtures of h~drogen fluoride and various other mineral acids such as orthophosphoric acid, fluorophosphoric acid, sulfuric acid, hydrochloric acid, etc. Although such mixtures are generally effective, experience has shown that many forma-tions do not respond to the acid treatment.
In general, hydrocarbon-bearing siliceous formations are of a heterogeneous nature and contain a variety of inor-ganic materials. In addition the pores of the formation may contain objectional deposits of organic matter such as viscous crude oil, waxes, asphaltenes and resin precipitates of petro-leum origin. Conventionally, before the acidizing treatment is begun this undesirable organic matter must be removed. Solvents such as carbon disulfide, carbon tetrachloride, or an aromatic hydrocarbon are first injected into the formation surrounding the well. This solvent treatment is repeated several t:imes .~
~ .
until the pores of the formation are relatively free of the organic material to insure a proper acidizing environment in the formation.
Another problem common to all methods of acidizing is the production of precipitates within the formation interstices through the action of the acid-treating reagent or its byproducts on some precipitate-forming constituent of the formation. This generally occurs when the acidizing fluid is spent and precipitates in a form which plugs the pores of the producing formation. As noted above, acidizing techniques have previously employed mixtures of phosphoric acid, generally referred to as orkhophosphoric acid, with other mineral acids.
~owever, the orthophosphates of pol~valent or heavy metals are all virtually insoluble in water. For example, calcium and magnesium compounds are found in all producing formations, and when attacked by phosphoric acid mixtures form insoluble phos-phates. The calcium and magnesium phosphates are especially .
difficult to remove and re~uire expensive procedures to revita-lize a producing formation. Therefore, there exists a need for a composition which will provide a "one shot" acidizing treatment which removes objectionable deposits of organic material, eliminating the need for a separate solvent treatment step, along with an acidic-treating reagent that does not form precipitates within the formation.
Accordingly, a principal object of this invention `
is to provide a novel composition and method for increasing the permeability of siliceous subterranean formations.
Another object is to provide a composition and method which remove both acid-soluble and oil-soluble compo-nents from the formation.
A further object is to provide a composition whlch does not form undesirable precipitates on reac-tion with the formation.
Other objects, advantages and ~eatures of the inven-tion will become apparent ~rom the following description and appended claims.
This invention provides a substantially anhydrous emulsion comprising (1) about 5 to 95 parts by weight of an acid component comprising (a) about 50 to 99 parts by weight of polyphosphoric acid having about S to 86 weight percent of the total P2O5 present as polymeric P2O5, (b) about 1 to 25 parts by weight of hydrofluoric acid, and (c) 0 to about 50 parts by weight of a catalyst selected from ~he group consis-ting of (A) strong mineral acids selected from the group con-sisting of sulfuric, nitric, perchloric and hydrochloric acids and mixtures thereof; (b) carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C) oxidizing agents selected from the group consisting of hydro-gen peroxide, potassium chromate, potassium permanganate and chromic acid; (2) about 5 to 95 parts by weight of an organic solvent component; (3) about 0.01 to 3.0 parts by weight of an anionic or nonionic surfactant component; and wherein -the H2O/P2O5 mole ratio of the overall emulsion is less than 3.4.
An em~odiment of the invention provides a substan-tially anhydrous emulsion comprising: (1) about 25 to 75 parts by weight of an acid component comprising (a) about 60 to 95 parts by weight of polyphosphoric acid having about ~0 to 75 weight percent of the total P2O5 present as polymeric P~O5, ~,~, I
(b) about 2 to 8 parts by weight of hydrofluoric acid and (c) about 2 to 40 parts by weight of a catalyst selected from the group consisting of (A~ strong mineral acids selected from the group consisting of sulfuric, nitric, perchloric and hydrochloric acids and mixtures thereof; (B~ carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C) oxidi-zing agents selected from the group consisting of hydrogen peroxide, potassium chromate, potassium permanganate and chromic acid; (2) about 25 to 75 parts by weight of an organic solvent composition comprising (a) about 40 to 65 parts by weight of a normally li~uid aliphatic hydrocarbon distillate boiling in the range of about 120~ to 550 F., (b) about 10 to 30 parts by weight of a normally liquid aromatic hydrocarbon, (c) about 1 to 5 parts by weight of an ether of an aliphatic alcohol, and (d) about 2 to 10 parts by weight of a lower alkyl monohydric alco-hol; (3) about 0.1 to 1.0 parts by weight of an anionic or nonionic surfactant component; and wherein the H2O/P2O5 mole ratio of the overall emulsion is between 2.2 and 2.8.
This invention further provides the method for in-creasing the permeability of a siliceous subterranean geological formation penetrated by a well which comprises lntroducing --through said well and into the formation surrounding said well a substantially anhydrous emulsion comprising: (1) about 5 to 95 parts by weight of an acid component comprising (a) about 50 to 99 parts by weight polyphosphoric acid, said polyphosphoric acid containiny about 5 to 86 weight percent of the total P2O5 present as polymeric P2O5, (b~ about 1 to 25 par~s by weight of hydro-fluoric acid, and (c) 0 to about 50 parts by weight of a catalyst selected from the group consisting of (A~ strong mineral acids selected from the group consisting of sulfuric, nitric, per-chloric and hydrochloric acids and mi~tures thereof; (~) , -4-organic carboxylic acids selected from the group consisting of formic, acetic, chloroacetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C~ oxidizing agents selected ~rom the group consisting of hydrogen peroxide, potassium chromateg potassium permanganate and chromic acid; (2) about 5 to 95 parts by weight of an organic solvent compo:nent; (3) about 0.01 to 3.0 parts by weight of an anionic or nonionic surfac-tant; and in which the ~I2O/P2O5 mo:Le ratio is less than 3.4 in the overall acid emulsion.
A further embodiment of the invention provides a siliceous subterranean geological formation penetrated by a well bore which comprises introducing into the formation a highly viscous, substantially anhydrous, liquid-acid-mixture composi-tion, comprising: (1) about 25 to 75 parts by weight of an acid component comprising (a) about 60 to 95 parts by weight polyphos-phoric acid, said polyphosphoric acid containing abou-t 40 to 75 weight percent of the total P2O5 present as polymeric P2O5, (b) about 2 to 8 parts by weight of hydrofluoric acid, and (c) about 2 to 40 parts by weight of a catalyst selected from the group consisting of (A) strong mineral acids selected from the group consisting of sulfuric, nitric, perchloric and hydro-chloric acids and mixtures thereof; (B) organic carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids;
and (C) oxidizing agents selected from the group consisting -of hydrogen peroxide, potassium chromate, potassium permanganate and chromic acid; (2) about 25 to 75 parts by weight of an organic solvent composition comprising (a) about 40 to 65 parts by weight o a normally li~uid aliphatic hydrocarbon distillate boiling in the range o about 120 to 550Q F., (b) about 10 to 30 parts by weight o a normall~ liquid aromatic hydrocarbon, (c) about 1 to 5 parts by weight of an -4a-~5~
ether of an aliphatic polyhydric alcohol, and (~) about 2 to 10 parts by weight of a lower monohydric a].cohol, and (3~ about 0.1 to 1.0 parts by weight o~ an anionic or nonionic surfactant, and in which the ~O~P2O5 mole ratio in the overall emulsion composition is between 2.2 and 2~.
A still further embodiment of the invention provides a method for increasing the permeability of a mixed subterranean geological formation penetrated by a well bore which comprises introducing into the formation a highly viscous, substantially anhydrous, liquid-acid-mixture composition, comprising: (1) about 5 to 75 parts by weight o~ an acid component compxising (a) about 50 to 99 parts by weight polyphosphoric acid, said polyphosphoric acid containing about 5 to 86 weight percent of the total P2O5 present as polymeric P205, (b) about 1 to about 25 parts by ~eight of hydrofluoric acid, and (c) 0 to about 50 parts by weight of a catalyst selected from the group consisting of (A) strong mineral acids selected from the group consisting of sulfuric, nitric, per-chloric and hydrochloric acids and mixtures thereof; (B) organic carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C) oxidizing agents selected from the group consisting of hydrogen peroxide, potassium chromate, potas-sium permanganate and chromic acid; (2) about 25 to 95 parts by weight of an organic solvent component; and (3) about 0.01 to 3.0 parts by weight of an anionic or nonionic suxfactant compo-nent, and wherein the H2O/P2OS mole ratio is from 2.1 to 3.4 in the overall acid emulsion.
A still ~urther embodiment of the invention provides a method for increasing the permeability of a mixed subterranean geological formation penetrated by a well bore which comprises introducing into the formation a highly viscous~ substantially anhydrous, liquid-acid-mixture composition, compxising~
j"~
about 20 to 50 parts by weight of an acid component comprising (a) about 60 to 95 parts by weight pol~phosphoric acid, said polyphosphoric acid containing about 40 to 75 weight percent of the total P2O5 present as polymeric P2O5, (b) about 2 to 8 parts by weight of hydrofluoric acid, and ~c) about 2 to 40 parts by weight of a catalyst selected from the group consisting of (A) strong mineral acids selected from the group consisting of sulfuric, nitric, perchloric and hydrochloric acids and mix-tures thereof; (B) organic carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, tri-chloracetic, citric, oxalic and maleic acids; and (C) o~idizin~
agents selected from the group consisting of hydrogen peroxide, potassium chromate, potassium permanganate and chromic acid; (2) about 50 to 80 parts by weight of an organic solvent composition comprising (a) about 40 to 65 parts by weight of a normally liquid aliphatic hydrocarbon distillate boiling in the range of about 120 to 550~ F., (b) about 10 to 30 parts by weight of a normally liquid aromatic hydrocarbon, (c) about l to 5 parts by weight of an ether of an aliphatic polyhydric alcohol, and (d) about 2 to 10 parts by weight of a lower al~yl monohydric alcohol; and (3) about 0.1 to 1.0 parts by weight of an anionic or nonion.ic surfactant, and which the H2O/P2O5 mole ratio in the overall emulsion composition is between 2.1 and 3.4c The invention relates to a non-a~ueous emulsion composition for increasing the permeability of siliceous subterranean geological formations, and to a method of acidizing which dissolves organic materials and avoids the formation of insoluble inorganic precipitates and many of the other difficul-ties encountered in prior art acidizing methods. The invention 3~ involves the injection into the formation of a novel, non-~. -4c-aqueous emulsion comprising a substantially anhydrous liquid polyphosphoric acid-based mixture, an organic solvent composi-tion, and a surface-active agent or surfactant. The acid com~ .
ponent of the emulsion comprise:s about 5 to 95 parts by weight of a substantially anhydrous liquid polyphosphoric acid-based :;
mixture comprising ~a) about 50 to 99 parts by weight polyphos-phoric acid with about 5 to 86 weight percent of the total P2O5 -present as polymeric P2O5, (b) about 1 to 25 parts by weight hydrofluoric acid, and (c) optionally, 0 to about 50 parts by weight of a catalyst selected from the group consisting of strong mineral acids, carboxylic acids, oxidizing compounds, and mix- ~ -tures thereof, in which the H2O/P2O5 mole ratio in the overall emulsion composition is less than 3.4. The emulsion also contains about 5 to 95 parts by weight of an organic solvent composition selected from the group consisting of polar solvents, hydrocar-bon solvents, and mixtures thereof; and about 0.01 to 3.0 parts by weight of a surfactant selected from the group consisting of anionic surfactants and nonionic surfactants.
This novel, non-aqueous emulsion composition can be utilized in both matrix acidizing and acid fracturing well stimulation pxocedures, and also has utility in many varied applications such as gas drying, extracting metals from ores, metal treatment, removing scale deposits from steam boilers and pipes, and particularly in methods where solvent treatment is desired along wtih acidizing action.
The drawing is a graph illustrating the relationship of the polymeric P2O5 content of the polyphosphoric acid ingre-dient of the emulsion composition as a function of the mole ratiO of H2O/P2O5~
The novel, non-aqueous acid emulsion of the pre.sent invention comprises an acid component, an organic solvent com-ponent and a surfactant capable of forming either an acid-in-solvent emulsion or a solvent-in-acid emulsion. The composition of the non-aqueous polyphosphoric acid-based emulsion employed in carrying out this invention will depend upon its ultimate use.
Compositions of non-aqueous acid emulsions comprising a mixture of about 5 to 95 parts by weight of the acid component; about 5 to 95 parts by weight o~ the organic solvent component; and about 0.01 to 3.0 parts by weight of an anionic or nonionic surfactant are encompassed by the invention.
10The non-aqueous acid emulsion compositions are pre-pared by: (1) adding the surfactant to the solvent component with moderate stirring, and ~2) adding this surfactant-solvent mixture to the acid component with moderate stirring to form the emulsion. The rate of addition of the surfactant-solvent mixture is critical and should be slow enough so as not to break the emulsion already formed. In an alternate method the surfactant is added to the acid component with moderate stir-ring and then the solvent component is blended into this acid ~-mixture. The rate of addition of components must also be con trolled to avoid breaking the emulsion. These methods provide stable emulsions which can be either solvent external-acid internal or acid external-solvent internal. It is generally preferred to use the solvent external-acid internal type emul-sion in treating formations. When this type of emulsion enters a formation pore the solvent first contacts and dissolves any organic material present, thus expo~ing the siliceous formation to the acid.
The general reactions involved in the attack of the substantially anhydrous liquid polyphosphoric-based acid emul-sions of this invention upon siliceous compounds are expressedby the following equation:
4P27 + sio2~ ~0_ -o-p-o~; + 2~1 ~ siF4~ ~P2O7+ ~2 O O
In the first step of the reaction, a phosphosilicate complex is formed. Under anhydrous conditions the soluble phos phosilicate complex then reacts with hydrofluoric acid to pro-duce a gas, silicon tetrafluoride, and to regenerate polyphos-phoric acid and water. The overall concept of this invention ; ?
is that the acid componen-t rapidly dissolves the silica and complexes other metals such as aluminum, iron, cobalt, nickel, copper, zinc, and the like. Polyphosphoric acid mixtures hav-ing a mole ratio of water to phosphorus pentoxide (H2O/P2O5) of between about 2.1 to 3.~, and particularly between about
2.2 and 2.8, form soluble complexes with most cations. Further-more, the polyphosphate complexes are stable after neutraliza-tion. The in situ formation of gaseous silicon tetrafluoride provides the additional benefit of sweeping and carrying undis-solved particles of debris through the ormation without plug-ging or bridging. Excess polyphosphoric acid is required to remove the ambient and produced water in order to keep the system in an anhydrous condition, i.e., maintaining the mole ratio of water to phosphorus pentoxide in the overall acid mixture below 3.4 and in emulsion form.
In the treatment of subterranean formations, a novel, non-aqueous emulsion composition is injected into a well and into contact with a siliceous subterranean formation containing a solid or semi-solid accumulation o~ hydrocarbons withln the formation pores. This novel, non-aqueous emulsion composition constitutes a "one shot" treatment with the solvent component removing the undesirable hydrocarbon accumulations from the pores of the formation, thus preconditioning the formation ~or the attack o~ the acid component of the emulsion. The emulsion is stable at temperatures existing in the wlell but subject to being broken by either contacting the pore-plugging hydrocar-bons or reacting with the silica formation.
In accordance with this invention, the exact emulsion used will depend largely upon the particular type of formation to be acidized. In predominantly siliceous geological forma-tions containing sandstone, shale or other siliceous rock com-positions, the acid component comprises about 5 to 95 parts by weight of a mixture comprising about 50 to 99 parts by weight polyphosphoric acid with about 5 to ~6 weight percent o-f the total P2O5 present as polymeric P2O5, about 1 to 25 parts by weight of hydrofluoric acid, and optionally up to about 50 parts by weight of a catalyst selected from the group consisting of strong mineral acids, organic carboxylic acids and o~idizing compounds, where the H2O/P2O5 mole ratio in the overall emulsion composition is between about 2.1 and 3.~. The solvent component constitutes about 5 to 95 parts by weight of a solvent blend comprising (a) about 35 to 80 parts by weight of a normally liquid aliphatic hydrocarbon distillate boiling within the range of about 120 F. to 550 F., (b) abou~ 4 to 40 parts by weight of a normally liquid aromatic hydrocarbon, (c) about 0.5 to 6 parts by weight of an ether of an aliphati~ polyhydric alcohol, and (d) about 1 to 12 parts by weight of a lower alkyl monohy-dric alcohol. The emulsion also contains about 0.01 to 3.0 parts by weight of an anionic or nonionic surfactant.
The preferred substantially anhydrous acid emulsions employed in treating siliceous formations comprise: (l) about '~'s ~
~ ~5~3 ~
25 to 75 parts by weight of an acid component comprising (a~
about 60 to 95 parts by weight polyphosphoric acid having about 40 to 75 weight percent of the total P2O5 present as polymeric P2O5, (b) about 2 to 8 parts by weight of hydro-fluoric acid, and tc) optionally, 2 to 40 parts by weight of a catalyst selected from strong mineral acids, carboxylic acids, and oxidizing compounds; (2) about 25 to 75 parts by weight of a solvent component comprising (a) about 40 to 65 parts by - ;.
weight of a normally liquid aliphatic hydrocarbon distillate boiling wtihin the range of 120 F. to 550 F., (b) about 10 to 30 parts by weight of a normally liquid aromatic hydrocarbon, (c) about 1 to 5 parts by weight of an ether of an aliphatic ~ ;
polyhydric alcohol and (d) about 2 to 10 parts by weight of an alkyl monohydric alcohol; and (3) about 0.1 to 1.0 parts by weight of an anionic or nonionic surfactant, and in which the ~2O/P2O5 mole ratio in the overall emulsion composition is between 2.2 and 2.8.
In mixed formations, i.e., formations containing cal-careous materials in admixture with siliceous materials, parti-cularly those formations containing less than 15 percent cal-careous material, it i~ preferred that the substantially anhy-drous liquid acid emulsion composition also contains hydro-chloric acid to aid in dissolving the calcareous materials.
However, it is also preferred that these emulsions contain less acid component than those previously described for use with predominantly siliceous formations. In treating mixed forma-tions there is more danger of a plugging material being pre-cipitated when the acid spenas on the formation than in treat-ing predominantly siliceous formations.
The compositions employed in treating mixed forma-tions broadly comprise the same ingredients and proportions as are utilized in treating siliceous formations except that the , ~ i `,?, ,? ¦ _ 9 _ ~56~3 .
acid component is present in about 5 to 75 parts by weight and the solvent component is present in about 25 to 95 parts by weight. Similarly, the preferred compositions for use in treating mixed formations comprise the same ingredients and proportions as are preferred for treating siliceous formations except that the acid component is present in about 20 to ~0 parts by weight and the solvent component is present in about 50 to 30 parts by weight.
The hydrofluoric acid component may be prepared in si~tu by adding crystalline ammonium bifluoride to hydro-chloric acid. The hydrogen chloride reacts with the bifluoride salt to form hydrogen fluoride. The more salt added, the greater will be the hydrogen fluoride concentration and the lower will be the hydrogen chloride concentration. Other pre-parative methods, including the mi~ing o hydrofluoria and hydrochloric acid solutions, can be employed. The use of such mixed acids is generally preferred.
The major ingredient of the acid component in the emulsion composition is polyphosphoric acid. Polyphosphoric acid is a generic term used to defined the phosphoric acids havin~ less water of constitution than orthophosphoric acid.
Orthophosphoric acid contains one atom of phosphorus per molecule and has a theoretical mole ratio of water to phos-phorus pentoxide of 3.0 or greater. Polyphosphoric acids have two or more atoms of phosphorus in a theoretical mole ratio of water to phosphorus pentoxide of less than 3. Polyphosphoric acid has two general forms, the acyclic and cyclic. The latter is commonly referred to as metaphosphoric acid. In the acyclic form, which is derived by limited molecular dehydration of orthophosphoric acid, the individual chains of phosphorus and oxygen atoms have termirlal ends and a theoretical mole ratio of . ,: :, water to phosphorus pentoxide of between 2 and 3. In metaphos~
phoric acid, which is derived from the acyclic form by continued molecular dehydration, the chain is endless, forming ring struc-tures. Metaphosphoric acids have theoretical mole ratios of water to phosphorus pentoxide of 2 or less. However, in some cases it is preferred that the concentration or dehydration of the orthophosphoric acid is stopped before the meta species begin to form. The reason is that the acyclic form of polyphos-phoric acid is a much better complexing agent for aluminum and transition metals like iron, cobalt, nickel, copper, zinc, etc.
Therefore, in geological formations which contain substantial amounts of compounds of the aforementioned metals, a polyphos-phoric acid-based acidizing mixture with little or no meta poly-phosphoric acid present would be most effective. Thus, the pre-ferred acid compositions exhibit H2V/P2O5 mole ratios above about The substantially anhydrous polyphosphoric acid com-ponent of the acid emulsion of this invention may be prepared from either furnace acid or wet process acid. The various com-ponents are introduced into a suitable vessel with agitation orstirring preferably in a closed vessel or system. Open vessels are provided with a cooling means to avoid fuming vapors which are generated by the exothermal mixing of the acid components.
The composition of this invention can be obtained by any suit-able method depending on the source materials used. For example, a dilute wet-process phosphoric acid is processed to polyphos-phoric acid by the addition of dilute, concentrated, or fuming sulfuric acid followed by concentration of the mixture through any suitable step, such as evaporation of water or by the addi-tion of anhydrous phosphorus pentoxide and anhydrous hydro-fluoric acid. When a polyphosphoric acid having an H2O/P2O5 mole ratio of less than 2.6 is used, it is preferred to add concentrated (98~ strength) sulfuric acid to avoid dilution of the P205 content. On the other hand, fu~ing sulfuric acid, sulfur trioxide, and/or hydrofluoric acid can be added to poly-phosphoric acid to obtain the proper percent of the other acids in the mixture. It i9 noted from the drawing that poly acid begins to form in the equilibrated acid at a mole ratio of water to P2O5 of about 3.6, i.e., an acid containing ahout 95 weight percent orthophosphoric acid and still containing about 5 weight pexcent of uncombined water. Although this composi-tion has some free water, the acid is herein referred to as a substantially anhydrous acid since it is anhydrous in a sense that it has reached its maximum concentration of orthophos- -phoric acid and further concentration increases the poly acid content.
The total P2O5 content of the non-aqueous polyphos-phoric based acid emulsion is determined by diluting a repre-sentative sample with water, adding perchloric and nitric acids and boiling the mixture to convert all forms of phosphoric acid to orthophosphoric acid. Samples are then passed over a cation exchange resin to replace the metal cations with hydrogen as these cations will interfere with subsequent analyses. The ion-exchanged sample is thereafter titrated with a strong base through two break-points, the first of which corresponds to the neutralization of the strong acids present, hydrochloric, ;~
nitric, etc., and the most strongly ionized hydrogen of the orthophosphoric acid. The second break-point in the titration curve occurs at a pH of about 9.5 to 10 and corresponds to neutralization of the second less strongly ionized hydrogen of the orthophosphoric acid. The difference in titer between these break-points corresponds to the total phosphate present which is reported as total P2O5.
5~
The water content of the acid existing as water of constitution and water of dilution is determined by placing a weighted portion of the acid in a crucible with zinc oxide in excess of that needed to react with the acid. The crucible is then weighed, dried at 100 C. for one hour and placed in an oven at 500 C. for an hour. The loss in weight corresponds to the total water present in the acid mixture.
To determine the amount of orthophosphoric acid pre-sent, various analytical techniques can be employed. Regard-less of the analytical method employed, prior thereto, the acidsample is prepared by dilution with water, and then acidifica-tion with concentraked sulfuric or nitric acid, followed by further dilution. Care should be ta]cen to avoid elevated tem-peratures and the sample preparation should be done in an ice bath to avoid hydrolysis of the polyphosphoric acid. The resultant solution is passed over a strong acid, cation-exchange resin, e.g., Amberlite IR-120~I resin*, to remove -the metallic cation impurities which interfere with subsequent analyses.
Immediately after passage over the resin, the acid should be neutralized to a pH of about 3.5 to about 6.0 to reduce the tendency of polyphosphoric acid to hydrolyze. The acid is thereafter titrated to the break-point, ~alling at a pH
between 9.5 and 10 corresponding to the neutralization of the second, ionized hydrogen of the orthophosphoric acid. There-after, an excess of a silver nitrate solution is added to pre-cipitate silver orthophosphate and release the third, very weakly ionized hydrogen ion o~ the orthophosphoric acid. The resultant solution is then titrated to determine the amlount of hydrogen ion released in the silver precipitation, and this titer value corresponds to the amount of orthophosphoric acid present in the sample which is reported on a P2O5 basis.
*Trademark G~3 The amount of phosphorus pentoxide existing in the form of polyphosphoric acid can be determined by the difference between the total P2O5 present and that existing as orthophos-phoric acid. When, however, the polyphosphoric acid is present in low concentrations, constituting 5 percent or less of the total P2O5 content, it is preferred to analyze for the polyphos-phoric acid directly by an anion exchange chromatography method such as described by Peters and Rieman in Analytica _himica Octa, 14, page 131 and by Weiner in Journal_Amer can Oil Chemist Society, 34, page 124.
Catalytic agents which can be used to catalyze the above-described general reaction are strong mineral acids, organic carboxylic acids and oxidizing compounds. These cataly~ts can be employed in concentration ranges of 0 to about 50 parts by weight and preferably in the range of about 2 to 40 parts by weight.
Strong mineral acids such as sulfuric, nitric, per-chloric and hydrochloric acids or mixtures thereof can be used.
One drawback with using sulfuric acid as a catalyst in acid mix-tures for treating hydrocarbon formations is the possibility ofsludge ~ormation due to sulfuric acid attack on formation hydro-carbons. However, for the other utilities mentioned above, sul-furic acid is preferred for, in addition to the catalytic effect, it aids in dehydration and depresses the freeæing point of poly-phosphoric acid to yield a final product having a freezing point of less than about 30 F., thereb~ insuring that the mixture is liquid at ambient temperatures. Furthermore, sulfuric acid has an additional and surprising effect on the viscosity of the phosphoric acid for it reduces the acid viscosity by 50 to 75 percent at concentrations of about 20 to 40 weight percent based on 100-percent-strength sulfuric acid, thereby allowing the use of a polyphosphoric acid with a lower mole ratio of water to phosphorus pentoxide.
Suitable organic carboxylic acids useful as catal~sts in the above-described reaction are those that form water-soluble or acid-soluble salts of alkali metals and alkaline earth metals. For example, formic, acetic, chloroacetic, pera-cetic, trichloroacetic, citric, oxalic and maleic acids can be used.
lypical oxidizing compounds which can be employed accoxding to this invention include hydrogen peroxide, potas-sium chromate, potassium permanganate and chromic acid.
The organic solvent component can be a hydrocarbon solvent, halogenated hydrocarbon, or a polar solvent or mixture~
thereof.
Hydrocarbon solvents such as petroleum solvents, petro-leum ether, petroleum naphtha, gasoline, petroleum spirit, var nish makers' and painters' naphtha, mineral spirit, kerosene, turbine fuel, high solvency petroleum naphthas, butanes, 2,2-dimethyl-butane, n-hexane, isohexane, n-heptane, isooctane, isoheptane, pentene-l, pentene-2, mixed pentenes, isoheptene, isooctenes, naphthas, benzene, toluene, toluene substitutes, ~ylene, solvent naphthas, ethylbenzene, diethylbenzene, iso-propylbenzene, amyl-benzene, diamylbenzene, triamylbenzene, tetraamylbenzene, dikeryl-benzene-12, amyltoluene, cyclohexane, methylcyclohexane, tetrahydronaphthalene, decahydronaphthalene~
diphenyl, coal-tar creosote, turpentine, terpene solvents, dipentene, pinene, p-cymene, p-menthane, pine oils, tall oils and crude oils are suitable.
~ lalogenated hydrocarbons such as methyl bromide, methyl chloride, dichloromerthane, chloroform, carbon tetra-chloride, ethyl chloride, ethylene dibromide, ethylene chlorobromide, ethylene dichloride, dichloroethylene, B-txichloro-ethane, trichloroethylene, trichloroethane, te-trabromoethane, 1,1,2,2-tetrachloroethane, tetrachloroethylene, pentachloro-ethane, hexachloroethane, isopropyl chloride, allyl chloride, propylene dichloride, mixed amyl chloride, n-amyl chloride, dichloropentanes, n-hexyl chloride, monochlorohydrin, dichloro-hydrin, epichlorohydrin, glycerol alpha-monochlorohydrin, glycerol alpha, gamma dichlorohydrins, monobromobenzenes, dibro-mobenzene, monochlorobenzene, o-dichlorobenzene, trichloro- ~.
benzene, a-chloronaphthalene, monoamyl chloronaphthalene, diamyl chloronaphthalene, dichloroethyl ether, dichlorodiiospropyl ether, triglycol dichloride, halowax oils, dichlorodifluoro-methane, difluorochloroethane, fluorodichloromethane, fluoro-trichloromethane, trifluorotrichloroethane, dichlorotetra-chloroethane and ethylidene fluoride can be used.
Polar solvents and mixtures thereof which can be employed include alcohols, ketones, ethers and esters. Alcohols such as methanol, ethanol, n-propyl alcohol, isopropanol, n-butanol, isobutyl alcohol, sec-butanol, tert-butanol, fusel oil, amyl alcohol, pentasol, n-amyl alcohol, sec-amyl alcohol, sec-n-amyl alcohol, methyl amyl alcohol, 2-ethylbutyl alcohol, heptanol 2, heptanol-3, 2-ethylhexanol, capryl alcohol, nonyl alcohol, nonyl alcohol derivatives, diisobutyl carbinol, n-decanol, undecanol, trimethyl-nonyl alcohol, tetradecanol, heptadecanol, phenol, benzyl alcohol, cyclohexanol, methyl-cyclohexanol, trimethylcyclohexanol, 4-tertamyl cyclohexyl alcohol, 4-tert-amyl cyclohexyl alcohol, dimethyl tolyl carhinol, furfuryl alcohol, tetrahydrofurfuryl alcohol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, tri-methyl glycol, triethylene glycol, polyethylene glycols, poly-propylene glycol 150, 2-methy:1.-2,4-pentane-diol, glycerol, terpene alcohol, alphaterpineol, fenchyl alcohol and hydroabietyl alcohols are useful.
Ketones such as acetone, methyl acetone, methyl ethyl ketone, methyl n~propyl ketone, methyl isobutyl ketone, methyl n-amyl ketone, ethyl butyl ketone, di-n-propyl ketone, methyl hexyl ketone, diisobutyl ketone, diacetone alcohol r acetonyl acetone~ mesityl oxide, cyclohexanone, methyl cyclohexanone, isophorone, and fenchone are suitable.
Ethers including ethyl ether, isopropyl ether, n-butyl ether, diamyl ether, n-hexyl ether, ethylene glycol monomethyl ether, "Cellosolve"*, ethylene glycol mono-n-butyl-ether, ethylene glycol monophenyl ether, ethylene glycol mono-benzyl ether, "Dowanol" 4**, "Dowanol" 3**, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, "Dowanol" 2**, diethyl acetal, 1,2-pro-pylene oxide, l,~dioxane, methylal, 2-methyl furan tetrahydro-furane, 2,3-dihydropyran, pentamethylene oxide, trioxane, ter-pinyl methyl ether, terpinyl ethylene glycol ether, dichloro-ethyl ether, triglycol dichloride, glyceryl ~-monoethyl ether, glyceryl ~-y-dimethyl ether, glyceryl ~-mono-n-butyl ether, glyceryl ~-monoisoamyl ether, and glyceryl ~-Y diisoamyl ether can be used.
Examples of esters which can be employed include methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, sec-butyl acetate, isobutyl acetate, amyl acetate, sec-amyl acetate, pentacetate, methyl amyl acetate, 2-ethyl butyl acetate, cyclohexyl acetate, methyl cyclohexanyl acetate, ethylene ylycol monoacetate, glycol diacetate, ethylene glycol monoacetate, glycol diacetate, ethylene glycol monomethyl e~her acetate, ethylene glycol monoethyl ether acetate, methoxy butyl ~cetate, methyl propionate, ethyl propionate, n-bu-tyl * A trademark of Union Carbide Corporation.
** A trademark of The Dow Chemical Company.
propionate, amyl propionate, ethy]. butyrate, methyl butyrate, n-butyl hutyrate, ethyl hydroxy-iso-butyra-te, diethyl carbonate, diethyl oxalate, dibutyl oxalate, diamyl oxalate, methyl formate, ethyl formate, butyl formate, amyl formate, methyl lactate, .
ethyl lactate, butyl lactate, amyl formate and ethyl silicate.
The surface-active agents or surfactants which can be employed in the practice of this invent:Lon are anionic sur-factants, nonionic surfactants and combinations thereof. Suit-able anionic surfactants are sulfonates characterized by the following generalized formula:
MSO3R ;
organo-sulfates characterized by the following generalized formula:
MSO4R ;
organo-phosphates characterized by the following generalized formula: ~
/ R :`
M2PO4R and MPO4 ~ R
wherein M is a cation, exemplary of which are hydrogen and alkali metals, such as sodium,potassium and lithium, and wherein R is a lipophilic organic group containing up to 200 carbon atoms, and usually containing from about 6 to 100 car-bon atoms, and which may also contain some hydrophilic func-tional groups, exemplary of which are alkyl, aryl, alkylaryl, alkenyl, alkenylaryl, alkylester, alkylpolyester, alkylether, alkylarylpolyether, cycloalkyl, naphyl, alkylmercaptyl, anthryl and alkylanthryl groups; and animal fat, vegetable oil, fatty acid and rosin derivatives.
Exemplary of the surface-active agents that can be employed in the practice of this invention are commercial surfactants, listed in Table 1.
::., .:
Company Trademark Chemical NONIONIC ETHERS
Wyandotte Chemical Pluronic L/62* Po:Lyoxyethylene, poly-Corp. oxypropylene Wyandotte Chemical Pluronic L/64* Polyoxyethylene, poly-Corp. oxypropylene Rohm & Haas Triton X-35* Octylphenoxy, polyoxy-ethylene ethanol Rohm ~ Haas Triton X-45* Octylphenoxy, poly-ethylene ethanol Rohm & HaasTriton X-100* Octy]phenoxy, polyoxy-ethylene ethanol Rohm & HassTriton X-165* Octylphenoxy, polyoxy-ethylene ethanol Rohm & HaasTriton X-305* Octylphenoxy, polyoxy~
ethylene ethanol Retzloff Chemical Retzonal NP-100* Alkylphenoxy, polyoxy-ethylene ethanol Thompson-IIaywardT-mulz 391* Alkylphenoxy, polyoxy-ethylene ethanol Trylon ChemicalsEmgard 2030* Alkylphenoxy~ polyoxy-ethylene ethanol NONIONIC ESTERS
Armour Ind. Chem. Ethofat 0/15* Polyethoxylated fatty acids Armour Ind. Chem. Ethofat C/15* Polyethoxylated fatcy acids Atlas Chemical Ind. Span 20* Sorbitan monolaurate *Trademark Compan~ Trademark Chemical Atlas Chemical Ind. Span 60* Sorbitan monostearate Atlas Chemical Ind. Tween 85* Polyoxyethylene sorbitan trioleate Baker Castor Oil Co. Surfactol* Glycerol monoricinoleate Baker Castor Oil Co. Surfactol 365* Ethoxylated castor oil ANIONIC SULFONATES
General Aniline & Igepon AC-78* Coconut oil acid, esters Film Corp. of sodium isethionate General Aniline & Igepon TN-74* Sodium N-methyl-N-palmi-Film Corp. toyl taurate General Aniline & Igepon TE-42* Sodium N-methyl-N-tallow Film Corp. acid taurate ~merican Cyanamid Aerosol OT* Dioctylester sodium sul-fosuccinic acid Mona Ind. Inc. Monawet DC-70* Dioctylester sodium sul-fosuccinic acid Calif. Chem. Ornite No. S* Alkylaryl sodium sulfo-nate Monsanto Co. Santonerse D* Alkylaryl sodium sulfo-nate ;
ANIONIC SU~FATES
EoI~ duPont Dupanol C* Sodium lauryl sulfate de Nemours & Co.
E.I. duPont Dupanol L-144* Sodium alkylaryl sulfate de Nemours & Co.
ANIONIC PHOSPHATES
General Aniline ~ Gafac PE-510* Free acid of a complex Film Corp. organic phosphate ester General Aniline & Gafac RE-610* Free acid of a complex Film Corp. organic phosphate ester *Trademark ~i6~3 Company Trademark Chernical General Aniline & Gafac MC-~70* Sodium salt of a complex Film Corp. organic phosphate ester ANIONIC MISClE~LLANEOUS
~ercules Inc. Dresinate 731* Sodium soap of a modified rosin Other additives such as acid inhibitors are not normally required in the emulsion. For example, at temperatures below 160 F. acid inhibitors are not necessary. However, if additi~es are employed, they should be compatible with the acid mixture. Suitable inhibitors useful above this temperature may include inorganic arsenic compounds and acetylenic alcohols, thiophenols, heterocyclic nitrogen compounds, substituted thioureas, rosin amine derivatives, quaternary ammonium compounds and similar organic agents.
The substantially anhydrous liquid phosphoric acid- -based emulsions of this invention can be used in both matrix acidizing and fracture acidizing. In matrix acidizing, the method of this invention is carried out by injecting the acid solution to be used into the producing formation surrounding the well. The injection pressure is kept below that necessary to fracture the formation so that penetration of the acid into the formation matrix occurs. The injection rate selected should 3 be generally sufficient to keep the pressure below that neces-sary to fracture the formation. The acid component of the invention has a high solubility for siliceous formations result-ing in products which are either solubilized or chelated in the form of low viscosity solutions. After the acid component has ~;
remained in contact with the exposed formation surfaces for a time sufficient to react therewith and to enlarge the ~ormation passages, the low viscosity reaction effluent is flushed from ' :~
the formation. Generally a spacer fluid, such as a low-boiling, low aromatic-containing aliphatic hydrocarbon, e.g., diesel oil, turbine fuel, etc., is injected followed by the injection of an after-flush fluid such as filtered crude oil, low calcium-con-taining water, etc. Injection of the afterflush fluid displaced the spacer fluid and the low viscosity reaction effluent and is continued until the desired quantity is introduced. The well may be returned to production as soon after the after-flush has been injected as is practicable.
The acid emulsions of this invention exhibit high viscosities under most reservoir conditions and are particularly useful in fracture acidi~ing; which treatment, due to much lPwer fluid loss, promotes the formation oE larger fractures and greater penetration than do the conventional fracturing tech-ni~ues. ~dditional benefits derived from the high viscosity characteristics of the acid mixtures of this invention is that gelling agents need not be added to the acidizing mixture, and the use of diverting agents in the acidizing operation may be avoided. Conventional fracture acidizing equipment may be used in this operation. As mentioned above, because of the high viscosity characteristics, the acid emulsions of this invention can function as both the fracturing fluid and the acidizing reagent. Conventional propping agents can be used. In some instances, it is desirable to employ a graded sand of uniform spherical granular configuration such as 20-40 mesh silica sand. ~ -This sand is retained within the fractured crevices after the acid mixture has been flushed therefrom and functions as a propping agent to retain the formation in a fractured condition.
The use of the acid emulsion of -this invention results in a greater increase in the permeability of the siliceous for-mation than if a slug of the acid component is either preceded -or followed by a slug of the solvent component. The emulsion is composed primarily of an intimate mixture of an acid phase and a solvent phase. When the emulsion contacts the formation each pore invaded by the emulsion will be exposed to acid and solvent at the same time. This insures maximum unplugging and enlargement of the affected pores. If the acid component and solvent component are injected as alternate slugs, they do not necessarily enter the same formation pores due to their differ-ing viscosities and wetting characteristics, and certainly are not available for permeability increasing action at the same time. Thus, the overall increase in permeability of the forma-tion is not as great as when the acid emulsion is used.
The acid emulsion is also effective in fingering into the formation for only a short distance and then diverting itself to form other short fingers. The acid emulsion is initially quite viscous. As the emulsion comes into contact with formation rock for the first time, the surfactant emulsi-fying agent tends to partially adsorb on the formation rock.
This sharply lowers the viscosity of that leading portion of the acid emulsion which is depleted in surfactant and allows this portion to penetrate or finger into the forrnation rock more easily~ However, as soon as a Einger has formed, the next portion of acid emulsion entering the finger encounters formation rock onto which surfactant has already been adsorbed.
Thus, this next portion of acid emulsion retains its high vis-cosity since its surfactant concentration is not depleted. This plugs the finger, discourages its further lengthening, and diverts the acid emulsion into fresh formation which has not previously been exposed to the acid emulsion.
The invention is further described by the following examples which are illustrative of specific modes of practicing the inven-tion as defined by the appended claims.
~
The substantially anhydrous acid emulsion of the present invention is prepared by adding 9.E~ gallons of Surfactol 395*, an ethox~lated castor oil, to 3,022 gallons `~
of an organic solvent admixture in a suitahle mixing tank.
The organic solvent is an admixture of 76.0 weight percent of ~et A, an aviation turbine fuel meeting AST~ standard specifi-cation D-1655 entitled "Standard Specification for Aviation Turbine Fuels, ASTM Standards, American Society for Testing Materials, part 17, November, 1971, pages 554-556, which speci-fication is herein incorporated by reference, 21.0 weight per- .
cent of toluene, 1.1 weight percent of ethylene glycol mono-butyl ether, and 1.9 weight perc~nt oE isopropanol. Next, this solvent-surfactant mixture is added, with moderate stirring, to 900 gallons of an acid mixture comprising 82 weight percent of polyphosphoric acid ~83 weight percent P2O5, 95 weight percent polymeric P2O5), 7 weight percent of hydrofluoric acid (70%
concentration) and 11 weight percent of hydrochloric acid (37~
concentration) in a stainless steel mixing tank equipped with a stirrer and a circulating water jacket. The rate of addition is controlled to prevent breaking the emulsion already formed.
This emulsion contains 60 weight percent of the organic solvent component, 0.25 weight percent of the surfactant component, and 40 weight percent of the acid component; and the ~20/P~O5 mole ratio of the overall emulsion is 2.7. The emulsion, thus pre-pared, is shipped to the well site.
EXAMPLE_2 A gravel-packed well completed in a sandstone forma-tion designed for the production of 200 barrels of high vis-cosity crude petroleum would produce only 10 percent of design * A trademark of Baker Castor Oil Co.
5 ~ 3 capacity. After the production is stopped, the well is treated in accordance with the invention by inject:ing a Eirst slug of 4,000 gallons of the emulsion described in Example 1 at a maximum differential pressure of 150 psi. Nex-t a second slug of
In the treatment of subterranean formations, a novel, non-aqueous emulsion composition is injected into a well and into contact with a siliceous subterranean formation containing a solid or semi-solid accumulation o~ hydrocarbons withln the formation pores. This novel, non-aqueous emulsion composition constitutes a "one shot" treatment with the solvent component removing the undesirable hydrocarbon accumulations from the pores of the formation, thus preconditioning the formation ~or the attack o~ the acid component of the emulsion. The emulsion is stable at temperatures existing in the wlell but subject to being broken by either contacting the pore-plugging hydrocar-bons or reacting with the silica formation.
In accordance with this invention, the exact emulsion used will depend largely upon the particular type of formation to be acidized. In predominantly siliceous geological forma-tions containing sandstone, shale or other siliceous rock com-positions, the acid component comprises about 5 to 95 parts by weight of a mixture comprising about 50 to 99 parts by weight polyphosphoric acid with about 5 to ~6 weight percent o-f the total P2O5 present as polymeric P2O5, about 1 to 25 parts by weight of hydrofluoric acid, and optionally up to about 50 parts by weight of a catalyst selected from the group consisting of strong mineral acids, organic carboxylic acids and o~idizing compounds, where the H2O/P2O5 mole ratio in the overall emulsion composition is between about 2.1 and 3.~. The solvent component constitutes about 5 to 95 parts by weight of a solvent blend comprising (a) about 35 to 80 parts by weight of a normally liquid aliphatic hydrocarbon distillate boiling within the range of about 120 F. to 550 F., (b) abou~ 4 to 40 parts by weight of a normally liquid aromatic hydrocarbon, (c) about 0.5 to 6 parts by weight of an ether of an aliphati~ polyhydric alcohol, and (d) about 1 to 12 parts by weight of a lower alkyl monohy-dric alcohol. The emulsion also contains about 0.01 to 3.0 parts by weight of an anionic or nonionic surfactant.
The preferred substantially anhydrous acid emulsions employed in treating siliceous formations comprise: (l) about '~'s ~
~ ~5~3 ~
25 to 75 parts by weight of an acid component comprising (a~
about 60 to 95 parts by weight polyphosphoric acid having about 40 to 75 weight percent of the total P2O5 present as polymeric P2O5, (b) about 2 to 8 parts by weight of hydro-fluoric acid, and tc) optionally, 2 to 40 parts by weight of a catalyst selected from strong mineral acids, carboxylic acids, and oxidizing compounds; (2) about 25 to 75 parts by weight of a solvent component comprising (a) about 40 to 65 parts by - ;.
weight of a normally liquid aliphatic hydrocarbon distillate boiling wtihin the range of 120 F. to 550 F., (b) about 10 to 30 parts by weight of a normally liquid aromatic hydrocarbon, (c) about 1 to 5 parts by weight of an ether of an aliphatic ~ ;
polyhydric alcohol and (d) about 2 to 10 parts by weight of an alkyl monohydric alcohol; and (3) about 0.1 to 1.0 parts by weight of an anionic or nonionic surfactant, and in which the ~2O/P2O5 mole ratio in the overall emulsion composition is between 2.2 and 2.8.
In mixed formations, i.e., formations containing cal-careous materials in admixture with siliceous materials, parti-cularly those formations containing less than 15 percent cal-careous material, it i~ preferred that the substantially anhy-drous liquid acid emulsion composition also contains hydro-chloric acid to aid in dissolving the calcareous materials.
However, it is also preferred that these emulsions contain less acid component than those previously described for use with predominantly siliceous formations. In treating mixed forma-tions there is more danger of a plugging material being pre-cipitated when the acid spenas on the formation than in treat-ing predominantly siliceous formations.
The compositions employed in treating mixed forma-tions broadly comprise the same ingredients and proportions as are utilized in treating siliceous formations except that the , ~ i `,?, ,? ¦ _ 9 _ ~56~3 .
acid component is present in about 5 to 75 parts by weight and the solvent component is present in about 25 to 95 parts by weight. Similarly, the preferred compositions for use in treating mixed formations comprise the same ingredients and proportions as are preferred for treating siliceous formations except that the acid component is present in about 20 to ~0 parts by weight and the solvent component is present in about 50 to 30 parts by weight.
The hydrofluoric acid component may be prepared in si~tu by adding crystalline ammonium bifluoride to hydro-chloric acid. The hydrogen chloride reacts with the bifluoride salt to form hydrogen fluoride. The more salt added, the greater will be the hydrogen fluoride concentration and the lower will be the hydrogen chloride concentration. Other pre-parative methods, including the mi~ing o hydrofluoria and hydrochloric acid solutions, can be employed. The use of such mixed acids is generally preferred.
The major ingredient of the acid component in the emulsion composition is polyphosphoric acid. Polyphosphoric acid is a generic term used to defined the phosphoric acids havin~ less water of constitution than orthophosphoric acid.
Orthophosphoric acid contains one atom of phosphorus per molecule and has a theoretical mole ratio of water to phos-phorus pentoxide of 3.0 or greater. Polyphosphoric acids have two or more atoms of phosphorus in a theoretical mole ratio of water to phosphorus pentoxide of less than 3. Polyphosphoric acid has two general forms, the acyclic and cyclic. The latter is commonly referred to as metaphosphoric acid. In the acyclic form, which is derived by limited molecular dehydration of orthophosphoric acid, the individual chains of phosphorus and oxygen atoms have termirlal ends and a theoretical mole ratio of . ,: :, water to phosphorus pentoxide of between 2 and 3. In metaphos~
phoric acid, which is derived from the acyclic form by continued molecular dehydration, the chain is endless, forming ring struc-tures. Metaphosphoric acids have theoretical mole ratios of water to phosphorus pentoxide of 2 or less. However, in some cases it is preferred that the concentration or dehydration of the orthophosphoric acid is stopped before the meta species begin to form. The reason is that the acyclic form of polyphos-phoric acid is a much better complexing agent for aluminum and transition metals like iron, cobalt, nickel, copper, zinc, etc.
Therefore, in geological formations which contain substantial amounts of compounds of the aforementioned metals, a polyphos-phoric acid-based acidizing mixture with little or no meta poly-phosphoric acid present would be most effective. Thus, the pre-ferred acid compositions exhibit H2V/P2O5 mole ratios above about The substantially anhydrous polyphosphoric acid com-ponent of the acid emulsion of this invention may be prepared from either furnace acid or wet process acid. The various com-ponents are introduced into a suitable vessel with agitation orstirring preferably in a closed vessel or system. Open vessels are provided with a cooling means to avoid fuming vapors which are generated by the exothermal mixing of the acid components.
The composition of this invention can be obtained by any suit-able method depending on the source materials used. For example, a dilute wet-process phosphoric acid is processed to polyphos-phoric acid by the addition of dilute, concentrated, or fuming sulfuric acid followed by concentration of the mixture through any suitable step, such as evaporation of water or by the addi-tion of anhydrous phosphorus pentoxide and anhydrous hydro-fluoric acid. When a polyphosphoric acid having an H2O/P2O5 mole ratio of less than 2.6 is used, it is preferred to add concentrated (98~ strength) sulfuric acid to avoid dilution of the P205 content. On the other hand, fu~ing sulfuric acid, sulfur trioxide, and/or hydrofluoric acid can be added to poly-phosphoric acid to obtain the proper percent of the other acids in the mixture. It i9 noted from the drawing that poly acid begins to form in the equilibrated acid at a mole ratio of water to P2O5 of about 3.6, i.e., an acid containing ahout 95 weight percent orthophosphoric acid and still containing about 5 weight pexcent of uncombined water. Although this composi-tion has some free water, the acid is herein referred to as a substantially anhydrous acid since it is anhydrous in a sense that it has reached its maximum concentration of orthophos- -phoric acid and further concentration increases the poly acid content.
The total P2O5 content of the non-aqueous polyphos-phoric based acid emulsion is determined by diluting a repre-sentative sample with water, adding perchloric and nitric acids and boiling the mixture to convert all forms of phosphoric acid to orthophosphoric acid. Samples are then passed over a cation exchange resin to replace the metal cations with hydrogen as these cations will interfere with subsequent analyses. The ion-exchanged sample is thereafter titrated with a strong base through two break-points, the first of which corresponds to the neutralization of the strong acids present, hydrochloric, ;~
nitric, etc., and the most strongly ionized hydrogen of the orthophosphoric acid. The second break-point in the titration curve occurs at a pH of about 9.5 to 10 and corresponds to neutralization of the second less strongly ionized hydrogen of the orthophosphoric acid. The difference in titer between these break-points corresponds to the total phosphate present which is reported as total P2O5.
5~
The water content of the acid existing as water of constitution and water of dilution is determined by placing a weighted portion of the acid in a crucible with zinc oxide in excess of that needed to react with the acid. The crucible is then weighed, dried at 100 C. for one hour and placed in an oven at 500 C. for an hour. The loss in weight corresponds to the total water present in the acid mixture.
To determine the amount of orthophosphoric acid pre-sent, various analytical techniques can be employed. Regard-less of the analytical method employed, prior thereto, the acidsample is prepared by dilution with water, and then acidifica-tion with concentraked sulfuric or nitric acid, followed by further dilution. Care should be ta]cen to avoid elevated tem-peratures and the sample preparation should be done in an ice bath to avoid hydrolysis of the polyphosphoric acid. The resultant solution is passed over a strong acid, cation-exchange resin, e.g., Amberlite IR-120~I resin*, to remove -the metallic cation impurities which interfere with subsequent analyses.
Immediately after passage over the resin, the acid should be neutralized to a pH of about 3.5 to about 6.0 to reduce the tendency of polyphosphoric acid to hydrolyze. The acid is thereafter titrated to the break-point, ~alling at a pH
between 9.5 and 10 corresponding to the neutralization of the second, ionized hydrogen of the orthophosphoric acid. There-after, an excess of a silver nitrate solution is added to pre-cipitate silver orthophosphate and release the third, very weakly ionized hydrogen ion o~ the orthophosphoric acid. The resultant solution is then titrated to determine the amlount of hydrogen ion released in the silver precipitation, and this titer value corresponds to the amount of orthophosphoric acid present in the sample which is reported on a P2O5 basis.
*Trademark G~3 The amount of phosphorus pentoxide existing in the form of polyphosphoric acid can be determined by the difference between the total P2O5 present and that existing as orthophos-phoric acid. When, however, the polyphosphoric acid is present in low concentrations, constituting 5 percent or less of the total P2O5 content, it is preferred to analyze for the polyphos-phoric acid directly by an anion exchange chromatography method such as described by Peters and Rieman in Analytica _himica Octa, 14, page 131 and by Weiner in Journal_Amer can Oil Chemist Society, 34, page 124.
Catalytic agents which can be used to catalyze the above-described general reaction are strong mineral acids, organic carboxylic acids and oxidizing compounds. These cataly~ts can be employed in concentration ranges of 0 to about 50 parts by weight and preferably in the range of about 2 to 40 parts by weight.
Strong mineral acids such as sulfuric, nitric, per-chloric and hydrochloric acids or mixtures thereof can be used.
One drawback with using sulfuric acid as a catalyst in acid mix-tures for treating hydrocarbon formations is the possibility ofsludge ~ormation due to sulfuric acid attack on formation hydro-carbons. However, for the other utilities mentioned above, sul-furic acid is preferred for, in addition to the catalytic effect, it aids in dehydration and depresses the freeæing point of poly-phosphoric acid to yield a final product having a freezing point of less than about 30 F., thereb~ insuring that the mixture is liquid at ambient temperatures. Furthermore, sulfuric acid has an additional and surprising effect on the viscosity of the phosphoric acid for it reduces the acid viscosity by 50 to 75 percent at concentrations of about 20 to 40 weight percent based on 100-percent-strength sulfuric acid, thereby allowing the use of a polyphosphoric acid with a lower mole ratio of water to phosphorus pentoxide.
Suitable organic carboxylic acids useful as catal~sts in the above-described reaction are those that form water-soluble or acid-soluble salts of alkali metals and alkaline earth metals. For example, formic, acetic, chloroacetic, pera-cetic, trichloroacetic, citric, oxalic and maleic acids can be used.
lypical oxidizing compounds which can be employed accoxding to this invention include hydrogen peroxide, potas-sium chromate, potassium permanganate and chromic acid.
The organic solvent component can be a hydrocarbon solvent, halogenated hydrocarbon, or a polar solvent or mixture~
thereof.
Hydrocarbon solvents such as petroleum solvents, petro-leum ether, petroleum naphtha, gasoline, petroleum spirit, var nish makers' and painters' naphtha, mineral spirit, kerosene, turbine fuel, high solvency petroleum naphthas, butanes, 2,2-dimethyl-butane, n-hexane, isohexane, n-heptane, isooctane, isoheptane, pentene-l, pentene-2, mixed pentenes, isoheptene, isooctenes, naphthas, benzene, toluene, toluene substitutes, ~ylene, solvent naphthas, ethylbenzene, diethylbenzene, iso-propylbenzene, amyl-benzene, diamylbenzene, triamylbenzene, tetraamylbenzene, dikeryl-benzene-12, amyltoluene, cyclohexane, methylcyclohexane, tetrahydronaphthalene, decahydronaphthalene~
diphenyl, coal-tar creosote, turpentine, terpene solvents, dipentene, pinene, p-cymene, p-menthane, pine oils, tall oils and crude oils are suitable.
~ lalogenated hydrocarbons such as methyl bromide, methyl chloride, dichloromerthane, chloroform, carbon tetra-chloride, ethyl chloride, ethylene dibromide, ethylene chlorobromide, ethylene dichloride, dichloroethylene, B-txichloro-ethane, trichloroethylene, trichloroethane, te-trabromoethane, 1,1,2,2-tetrachloroethane, tetrachloroethylene, pentachloro-ethane, hexachloroethane, isopropyl chloride, allyl chloride, propylene dichloride, mixed amyl chloride, n-amyl chloride, dichloropentanes, n-hexyl chloride, monochlorohydrin, dichloro-hydrin, epichlorohydrin, glycerol alpha-monochlorohydrin, glycerol alpha, gamma dichlorohydrins, monobromobenzenes, dibro-mobenzene, monochlorobenzene, o-dichlorobenzene, trichloro- ~.
benzene, a-chloronaphthalene, monoamyl chloronaphthalene, diamyl chloronaphthalene, dichloroethyl ether, dichlorodiiospropyl ether, triglycol dichloride, halowax oils, dichlorodifluoro-methane, difluorochloroethane, fluorodichloromethane, fluoro-trichloromethane, trifluorotrichloroethane, dichlorotetra-chloroethane and ethylidene fluoride can be used.
Polar solvents and mixtures thereof which can be employed include alcohols, ketones, ethers and esters. Alcohols such as methanol, ethanol, n-propyl alcohol, isopropanol, n-butanol, isobutyl alcohol, sec-butanol, tert-butanol, fusel oil, amyl alcohol, pentasol, n-amyl alcohol, sec-amyl alcohol, sec-n-amyl alcohol, methyl amyl alcohol, 2-ethylbutyl alcohol, heptanol 2, heptanol-3, 2-ethylhexanol, capryl alcohol, nonyl alcohol, nonyl alcohol derivatives, diisobutyl carbinol, n-decanol, undecanol, trimethyl-nonyl alcohol, tetradecanol, heptadecanol, phenol, benzyl alcohol, cyclohexanol, methyl-cyclohexanol, trimethylcyclohexanol, 4-tertamyl cyclohexyl alcohol, 4-tert-amyl cyclohexyl alcohol, dimethyl tolyl carhinol, furfuryl alcohol, tetrahydrofurfuryl alcohol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, tri-methyl glycol, triethylene glycol, polyethylene glycols, poly-propylene glycol 150, 2-methy:1.-2,4-pentane-diol, glycerol, terpene alcohol, alphaterpineol, fenchyl alcohol and hydroabietyl alcohols are useful.
Ketones such as acetone, methyl acetone, methyl ethyl ketone, methyl n~propyl ketone, methyl isobutyl ketone, methyl n-amyl ketone, ethyl butyl ketone, di-n-propyl ketone, methyl hexyl ketone, diisobutyl ketone, diacetone alcohol r acetonyl acetone~ mesityl oxide, cyclohexanone, methyl cyclohexanone, isophorone, and fenchone are suitable.
Ethers including ethyl ether, isopropyl ether, n-butyl ether, diamyl ether, n-hexyl ether, ethylene glycol monomethyl ether, "Cellosolve"*, ethylene glycol mono-n-butyl-ether, ethylene glycol monophenyl ether, ethylene glycol mono-benzyl ether, "Dowanol" 4**, "Dowanol" 3**, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, "Dowanol" 2**, diethyl acetal, 1,2-pro-pylene oxide, l,~dioxane, methylal, 2-methyl furan tetrahydro-furane, 2,3-dihydropyran, pentamethylene oxide, trioxane, ter-pinyl methyl ether, terpinyl ethylene glycol ether, dichloro-ethyl ether, triglycol dichloride, glyceryl ~-monoethyl ether, glyceryl ~-y-dimethyl ether, glyceryl ~-mono-n-butyl ether, glyceryl ~-monoisoamyl ether, and glyceryl ~-Y diisoamyl ether can be used.
Examples of esters which can be employed include methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, sec-butyl acetate, isobutyl acetate, amyl acetate, sec-amyl acetate, pentacetate, methyl amyl acetate, 2-ethyl butyl acetate, cyclohexyl acetate, methyl cyclohexanyl acetate, ethylene ylycol monoacetate, glycol diacetate, ethylene glycol monoacetate, glycol diacetate, ethylene glycol monomethyl e~her acetate, ethylene glycol monoethyl ether acetate, methoxy butyl ~cetate, methyl propionate, ethyl propionate, n-bu-tyl * A trademark of Union Carbide Corporation.
** A trademark of The Dow Chemical Company.
propionate, amyl propionate, ethy]. butyrate, methyl butyrate, n-butyl hutyrate, ethyl hydroxy-iso-butyra-te, diethyl carbonate, diethyl oxalate, dibutyl oxalate, diamyl oxalate, methyl formate, ethyl formate, butyl formate, amyl formate, methyl lactate, .
ethyl lactate, butyl lactate, amyl formate and ethyl silicate.
The surface-active agents or surfactants which can be employed in the practice of this invent:Lon are anionic sur-factants, nonionic surfactants and combinations thereof. Suit-able anionic surfactants are sulfonates characterized by the following generalized formula:
MSO3R ;
organo-sulfates characterized by the following generalized formula:
MSO4R ;
organo-phosphates characterized by the following generalized formula: ~
/ R :`
M2PO4R and MPO4 ~ R
wherein M is a cation, exemplary of which are hydrogen and alkali metals, such as sodium,potassium and lithium, and wherein R is a lipophilic organic group containing up to 200 carbon atoms, and usually containing from about 6 to 100 car-bon atoms, and which may also contain some hydrophilic func-tional groups, exemplary of which are alkyl, aryl, alkylaryl, alkenyl, alkenylaryl, alkylester, alkylpolyester, alkylether, alkylarylpolyether, cycloalkyl, naphyl, alkylmercaptyl, anthryl and alkylanthryl groups; and animal fat, vegetable oil, fatty acid and rosin derivatives.
Exemplary of the surface-active agents that can be employed in the practice of this invention are commercial surfactants, listed in Table 1.
::., .:
Company Trademark Chemical NONIONIC ETHERS
Wyandotte Chemical Pluronic L/62* Po:Lyoxyethylene, poly-Corp. oxypropylene Wyandotte Chemical Pluronic L/64* Polyoxyethylene, poly-Corp. oxypropylene Rohm & Haas Triton X-35* Octylphenoxy, polyoxy-ethylene ethanol Rohm ~ Haas Triton X-45* Octylphenoxy, poly-ethylene ethanol Rohm & HaasTriton X-100* Octy]phenoxy, polyoxy-ethylene ethanol Rohm & HassTriton X-165* Octylphenoxy, polyoxy-ethylene ethanol Rohm & HaasTriton X-305* Octylphenoxy, polyoxy~
ethylene ethanol Retzloff Chemical Retzonal NP-100* Alkylphenoxy, polyoxy-ethylene ethanol Thompson-IIaywardT-mulz 391* Alkylphenoxy, polyoxy-ethylene ethanol Trylon ChemicalsEmgard 2030* Alkylphenoxy~ polyoxy-ethylene ethanol NONIONIC ESTERS
Armour Ind. Chem. Ethofat 0/15* Polyethoxylated fatty acids Armour Ind. Chem. Ethofat C/15* Polyethoxylated fatcy acids Atlas Chemical Ind. Span 20* Sorbitan monolaurate *Trademark Compan~ Trademark Chemical Atlas Chemical Ind. Span 60* Sorbitan monostearate Atlas Chemical Ind. Tween 85* Polyoxyethylene sorbitan trioleate Baker Castor Oil Co. Surfactol* Glycerol monoricinoleate Baker Castor Oil Co. Surfactol 365* Ethoxylated castor oil ANIONIC SULFONATES
General Aniline & Igepon AC-78* Coconut oil acid, esters Film Corp. of sodium isethionate General Aniline & Igepon TN-74* Sodium N-methyl-N-palmi-Film Corp. toyl taurate General Aniline & Igepon TE-42* Sodium N-methyl-N-tallow Film Corp. acid taurate ~merican Cyanamid Aerosol OT* Dioctylester sodium sul-fosuccinic acid Mona Ind. Inc. Monawet DC-70* Dioctylester sodium sul-fosuccinic acid Calif. Chem. Ornite No. S* Alkylaryl sodium sulfo-nate Monsanto Co. Santonerse D* Alkylaryl sodium sulfo-nate ;
ANIONIC SU~FATES
EoI~ duPont Dupanol C* Sodium lauryl sulfate de Nemours & Co.
E.I. duPont Dupanol L-144* Sodium alkylaryl sulfate de Nemours & Co.
ANIONIC PHOSPHATES
General Aniline ~ Gafac PE-510* Free acid of a complex Film Corp. organic phosphate ester General Aniline & Gafac RE-610* Free acid of a complex Film Corp. organic phosphate ester *Trademark ~i6~3 Company Trademark Chernical General Aniline & Gafac MC-~70* Sodium salt of a complex Film Corp. organic phosphate ester ANIONIC MISClE~LLANEOUS
~ercules Inc. Dresinate 731* Sodium soap of a modified rosin Other additives such as acid inhibitors are not normally required in the emulsion. For example, at temperatures below 160 F. acid inhibitors are not necessary. However, if additi~es are employed, they should be compatible with the acid mixture. Suitable inhibitors useful above this temperature may include inorganic arsenic compounds and acetylenic alcohols, thiophenols, heterocyclic nitrogen compounds, substituted thioureas, rosin amine derivatives, quaternary ammonium compounds and similar organic agents.
The substantially anhydrous liquid phosphoric acid- -based emulsions of this invention can be used in both matrix acidizing and fracture acidizing. In matrix acidizing, the method of this invention is carried out by injecting the acid solution to be used into the producing formation surrounding the well. The injection pressure is kept below that necessary to fracture the formation so that penetration of the acid into the formation matrix occurs. The injection rate selected should 3 be generally sufficient to keep the pressure below that neces-sary to fracture the formation. The acid component of the invention has a high solubility for siliceous formations result-ing in products which are either solubilized or chelated in the form of low viscosity solutions. After the acid component has ~;
remained in contact with the exposed formation surfaces for a time sufficient to react therewith and to enlarge the ~ormation passages, the low viscosity reaction effluent is flushed from ' :~
the formation. Generally a spacer fluid, such as a low-boiling, low aromatic-containing aliphatic hydrocarbon, e.g., diesel oil, turbine fuel, etc., is injected followed by the injection of an after-flush fluid such as filtered crude oil, low calcium-con-taining water, etc. Injection of the afterflush fluid displaced the spacer fluid and the low viscosity reaction effluent and is continued until the desired quantity is introduced. The well may be returned to production as soon after the after-flush has been injected as is practicable.
The acid emulsions of this invention exhibit high viscosities under most reservoir conditions and are particularly useful in fracture acidi~ing; which treatment, due to much lPwer fluid loss, promotes the formation oE larger fractures and greater penetration than do the conventional fracturing tech-ni~ues. ~dditional benefits derived from the high viscosity characteristics of the acid mixtures of this invention is that gelling agents need not be added to the acidizing mixture, and the use of diverting agents in the acidizing operation may be avoided. Conventional fracture acidizing equipment may be used in this operation. As mentioned above, because of the high viscosity characteristics, the acid emulsions of this invention can function as both the fracturing fluid and the acidizing reagent. Conventional propping agents can be used. In some instances, it is desirable to employ a graded sand of uniform spherical granular configuration such as 20-40 mesh silica sand. ~ -This sand is retained within the fractured crevices after the acid mixture has been flushed therefrom and functions as a propping agent to retain the formation in a fractured condition.
The use of the acid emulsion of -this invention results in a greater increase in the permeability of the siliceous for-mation than if a slug of the acid component is either preceded -or followed by a slug of the solvent component. The emulsion is composed primarily of an intimate mixture of an acid phase and a solvent phase. When the emulsion contacts the formation each pore invaded by the emulsion will be exposed to acid and solvent at the same time. This insures maximum unplugging and enlargement of the affected pores. If the acid component and solvent component are injected as alternate slugs, they do not necessarily enter the same formation pores due to their differ-ing viscosities and wetting characteristics, and certainly are not available for permeability increasing action at the same time. Thus, the overall increase in permeability of the forma-tion is not as great as when the acid emulsion is used.
The acid emulsion is also effective in fingering into the formation for only a short distance and then diverting itself to form other short fingers. The acid emulsion is initially quite viscous. As the emulsion comes into contact with formation rock for the first time, the surfactant emulsi-fying agent tends to partially adsorb on the formation rock.
This sharply lowers the viscosity of that leading portion of the acid emulsion which is depleted in surfactant and allows this portion to penetrate or finger into the forrnation rock more easily~ However, as soon as a Einger has formed, the next portion of acid emulsion entering the finger encounters formation rock onto which surfactant has already been adsorbed.
Thus, this next portion of acid emulsion retains its high vis-cosity since its surfactant concentration is not depleted. This plugs the finger, discourages its further lengthening, and diverts the acid emulsion into fresh formation which has not previously been exposed to the acid emulsion.
The invention is further described by the following examples which are illustrative of specific modes of practicing the inven-tion as defined by the appended claims.
~
The substantially anhydrous acid emulsion of the present invention is prepared by adding 9.E~ gallons of Surfactol 395*, an ethox~lated castor oil, to 3,022 gallons `~
of an organic solvent admixture in a suitahle mixing tank.
The organic solvent is an admixture of 76.0 weight percent of ~et A, an aviation turbine fuel meeting AST~ standard specifi-cation D-1655 entitled "Standard Specification for Aviation Turbine Fuels, ASTM Standards, American Society for Testing Materials, part 17, November, 1971, pages 554-556, which speci-fication is herein incorporated by reference, 21.0 weight per- .
cent of toluene, 1.1 weight percent of ethylene glycol mono-butyl ether, and 1.9 weight perc~nt oE isopropanol. Next, this solvent-surfactant mixture is added, with moderate stirring, to 900 gallons of an acid mixture comprising 82 weight percent of polyphosphoric acid ~83 weight percent P2O5, 95 weight percent polymeric P2O5), 7 weight percent of hydrofluoric acid (70%
concentration) and 11 weight percent of hydrochloric acid (37~
concentration) in a stainless steel mixing tank equipped with a stirrer and a circulating water jacket. The rate of addition is controlled to prevent breaking the emulsion already formed.
This emulsion contains 60 weight percent of the organic solvent component, 0.25 weight percent of the surfactant component, and 40 weight percent of the acid component; and the ~20/P~O5 mole ratio of the overall emulsion is 2.7. The emulsion, thus pre-pared, is shipped to the well site.
EXAMPLE_2 A gravel-packed well completed in a sandstone forma-tion designed for the production of 200 barrels of high vis-cosity crude petroleum would produce only 10 percent of design * A trademark of Baker Castor Oil Co.
5 ~ 3 capacity. After the production is stopped, the well is treated in accordance with the invention by inject:ing a Eirst slug of 4,000 gallons of the emulsion described in Example 1 at a maximum differential pressure of 150 psi. Nex-t a second slug of
3,000 gallons of the same emulsion is injected at a rate of l/2 to 2 barrels per minute and at pressures below the fracturing pressure. After the acid treatment is complete, 200 barrels of turbine fuel ~et A, followed by lO0 barrels of filtered brine, are injected as an aEterflush. This stimulation treatment results in an immediate increase in petroleum production of 160 barrels per day.
This example illustrates the use of the method of the invention in fracture-acidizing a subterranean oil-producing formation. A production well is completed in a sandstone forma-tion with perfoxations in the interval between 2,722 and 3,075 feet, and begins producing only l barrel of oil and 4~ barrels of water per day. Following the preparation of the emulsion described in Example l, injection operations are commenced.
The emulsion is injected into the well unti] ahout 6,000 gallons have been introduced. The pressure initially increases and then falls off, indica~ing that the formation has bro]cen down and that the fracture has been initiated. This initial volume of acid emulsion is followed immediately with 3,000 gallons of 40-gravity lease crude containing about 4 pounds per gallon of small, solid particles of sand suspended therein as a propping agent. An additional volume of 3,000 gallons oE the acid emul-sion is then injected. The second and third stages of the frac-turing operation are performed using the emulsion compositions and volumes employed in the first stage.
The injection rate of the emulsion fracturing fluid is ~etween about lO and 16 barrels per minu-te, and the wellhead pressure ranges from about 4,700 to 5,500 psi Eor the first 'f~ ;6~3 stage, and between about 5,000 and 6,000 psi for the second and third stages.
Following the treatment, the well is shut in over-night. When the well is returned to production, it initially flows at the rate of 345 barrels of oil and 330 barrels of water per day. A week after the acid emulsion treatment, the average production is 360 barrels of oil and 263 barrels of water per day.
While particular embodiments of the invention have been described, it will be understood, of course, that the invention is not limited thereto since many modiEications can be made and it is intended to include within the invention such modifications as are within the scope o~ the claims.
The invention having thus been described, we claim:
This example illustrates the use of the method of the invention in fracture-acidizing a subterranean oil-producing formation. A production well is completed in a sandstone forma-tion with perfoxations in the interval between 2,722 and 3,075 feet, and begins producing only l barrel of oil and 4~ barrels of water per day. Following the preparation of the emulsion described in Example l, injection operations are commenced.
The emulsion is injected into the well unti] ahout 6,000 gallons have been introduced. The pressure initially increases and then falls off, indica~ing that the formation has bro]cen down and that the fracture has been initiated. This initial volume of acid emulsion is followed immediately with 3,000 gallons of 40-gravity lease crude containing about 4 pounds per gallon of small, solid particles of sand suspended therein as a propping agent. An additional volume of 3,000 gallons oE the acid emul-sion is then injected. The second and third stages of the frac-turing operation are performed using the emulsion compositions and volumes employed in the first stage.
The injection rate of the emulsion fracturing fluid is ~etween about lO and 16 barrels per minu-te, and the wellhead pressure ranges from about 4,700 to 5,500 psi Eor the first 'f~ ;6~3 stage, and between about 5,000 and 6,000 psi for the second and third stages.
Following the treatment, the well is shut in over-night. When the well is returned to production, it initially flows at the rate of 345 barrels of oil and 330 barrels of water per day. A week after the acid emulsion treatment, the average production is 360 barrels of oil and 263 barrels of water per day.
While particular embodiments of the invention have been described, it will be understood, of course, that the invention is not limited thereto since many modiEications can be made and it is intended to include within the invention such modifications as are within the scope o~ the claims.
The invention having thus been described, we claim:
Claims (28)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A substantially anhydrous emulsion comprising (1) about 5 to 95 parts by weight of an acid component com-prising (a) about 50 to 99 parts by weight of polyphosphoric acid having about 5 to 86 weight percent of the total P205 present as polymeric P205, (b) about 1 to 25 parts by weight of hydrofluoric acid, and (c) 0 to about 50 parts by weight of a catalyst selected from the group consisting of (A) strong mineral acids selected from the group consisting of sulfuric, nitric, perchloric and hydrochloric acids and mixture thereof; (B) carboxylic acids selected from the group consis-ting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C) oxidizing agents se-lected from the group consisting of hydrogen peroxide, potassium chromate, potassium permanganate and chromic acid; (2) about 5 to 95 parts by weight of an organic solvent component; (3) about 0.01 to 3.0 parts by weight of an anionic or nonionic surfactant component; and wherein the H20/P205 mole ratio of the overall emulsion is less than 3.4.
2. The emulsion defined in claim 1 wherein said strong mineral acid is hydrochloric acid.
3. The emulsion defined in claim 1 wherein said strong mineral acid is sulfuric acid.
4. The emulsion defined in claim 1 wherein said organic solvent component is selected from the group consisting of hydrocarbon solvents, halogenated hydrocarbon solvents, polar solvents, and admixtures thereof.
5. The emulsion defined in claim 4 wherein said organic solvent component comprises about 35 to 80 parts by weight of a normally liquid aliphatic hydrocarbon distillate boiling in the range of about 120° to 550° F.; about 4 to 40 parts by weight of a normally liquid aromatic hydrocarbon;
about 0.5 to 6 parts by weight of an ether of an aliphatic polyhydric alcohol; and about 1 to 12 parts by weight of a lower alkyl monohydric alcohol.
about 0.5 to 6 parts by weight of an ether of an aliphatic polyhydric alcohol; and about 1 to 12 parts by weight of a lower alkyl monohydric alcohol.
6. The emulsion defined in claim 1 comprising about 20 to 50 parts by weight of said acid component and about 50 to 80 parts by weight of said organic solvent com-ponent.
7. A substantially anhydrous emulsion comprising:
(1) about 25 to 75 parts by weight of an acid component com-prising (a) about 60 to 95 parts by weight of polyphosphoric acid having about 40 to 75 weight percent of the total P2O5 present as polymeric P2O5, (b) about 2 to 8 parts by weight of hydrofluoric acid and (c) about 2 to 40 parts by weight of a catalyst selected from the group consisting of (A) strong mineral acids selected from the group consisting of sulfuric, nitric, perchloric and hydrochloric acids and mixtures thereof; (B) carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C) oxidizing agents selected from the group consisting of hydrogen peroxide, potassium chromate, potassium permanganate and chromic acid; (2) about 25 to 75 parts by weight of an organic solvent composition comprising (a) about 40 to 65 parts by weight of a normally liquid aliphatic hydrocarbon distillate boiling in the range of about 120° to 550° F., (b) about 10 to 30 parts by weight of a normally liquid aromatic hydrocarbon, (c) about 1 to 5 parts by weight of an ether of an aliphatic alcohol, and (d) about 2 to 10 parts by weight of a lower alkyl monohydric alcohol; (3) about 0.1 to 1.0 parts by weight of an anionic or nonionic surfactant com-ponent; and wherein the H20/P205 mole ratio of the overall emulsion is between 2.2 and 2.8.
(1) about 25 to 75 parts by weight of an acid component com-prising (a) about 60 to 95 parts by weight of polyphosphoric acid having about 40 to 75 weight percent of the total P2O5 present as polymeric P2O5, (b) about 2 to 8 parts by weight of hydrofluoric acid and (c) about 2 to 40 parts by weight of a catalyst selected from the group consisting of (A) strong mineral acids selected from the group consisting of sulfuric, nitric, perchloric and hydrochloric acids and mixtures thereof; (B) carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C) oxidizing agents selected from the group consisting of hydrogen peroxide, potassium chromate, potassium permanganate and chromic acid; (2) about 25 to 75 parts by weight of an organic solvent composition comprising (a) about 40 to 65 parts by weight of a normally liquid aliphatic hydrocarbon distillate boiling in the range of about 120° to 550° F., (b) about 10 to 30 parts by weight of a normally liquid aromatic hydrocarbon, (c) about 1 to 5 parts by weight of an ether of an aliphatic alcohol, and (d) about 2 to 10 parts by weight of a lower alkyl monohydric alcohol; (3) about 0.1 to 1.0 parts by weight of an anionic or nonionic surfactant com-ponent; and wherein the H20/P205 mole ratio of the overall emulsion is between 2.2 and 2.8.
8. The emulsion defined in claim 7 wherein said strong mineral acia is hydrochloric acid.
9. The emulsion defined in claim 7 wherein said strong mineral acid is sulfuric acid.
10. The method for increasing the permeability of a siliceous subterranean geological formation penetrated by a well which comprises introducing through said well and into the formation surrounding said well a substantially anhy-drous emulsion comprising: (1) about 5 to 95 parts by weight of an acid component comprising (a) about 50 to 99 parts by weight polyphosphoric acid, said polyphosphoric acid contain-ing about 5 to 86 weight percent of the total P205 present as polymeric P205, (b) about 1 to 25 parts by weight of hydro-fluoric acid, and (c) 0 to about 50 parts by weight of a catalyst selected from the group consisting of (A) strong mineral acids selected from the group consisting of sulfuric, nitric, perchloric and hydrochloric acids and mixtures thereof;
(B) organic carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C) oxidizing agents se-lected from the group consisting of hydrogen peroxide, potas-sium chromate, potassium permanganate and chromic acid; (2) about 5 to 95 parts by weight of an organic solvent component;
(3) about 0.01 to 3.0 parts by weight of an anionic or nonionic surfactant; and in which the H20/P205 mole ratio is less than 3.4 in the overall acid emulsion.
(B) organic carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C) oxidizing agents se-lected from the group consisting of hydrogen peroxide, potas-sium chromate, potassium permanganate and chromic acid; (2) about 5 to 95 parts by weight of an organic solvent component;
(3) about 0.01 to 3.0 parts by weight of an anionic or nonionic surfactant; and in which the H20/P205 mole ratio is less than 3.4 in the overall acid emulsion.
11. The method defined in claim 10 wherein said acid component contains hydrochloric acid.
12. The method defined in claim 10 wherein said organic solvent component is selected from the group consis-ting of hydrocarbon solvents, halogenated hydrocarbon sol-vents, polar solvents, and admixtures thereof.
13. The method defined in claim 12 wherein said organic solvent component comprises about 35 to 80 parts by weight of a normally liquid aliphatic hydrocarbon distillate boiling in the range of about 120° F. to 550° F.; about 4 to 40 parts by weight of a normally liquid aromatic hydrocar-bon; about 0.5 to 6 parts by weight of an ether of an ali-phatic polyhydric alcohol; and about l to 12 parts by weight of a lower alkyl monohydric alcohol.
14. The method of claim 10 wherein the substan-tially anhydrous liquid acid composition is introduced into the formation surrounding the well bore at a pressure below the fracture pressure of the formation.
15. The method of claim 10 wherein the substanti-ally anhydrous liquid acid composition is introduced into the formation surrounding the well bore at a pressure at least equal to the fracture pressure of the formation.
16. A method for increasing the permeability of a siliceous subterranean geological formation penetrated by a wellbore which comprises introducing into the formation a highly viscous, substantially anhydrous, liquid-acid-mixture composition, comprising: (1) about 25 to 75 parts by weight of an acid component comprising (a) about 60 to 95 parts by weight polyphosphoric acid, said polyphosphoric acid contain-ing about 40 to 75 weight percent of the total P2O5 present as polymeric P2O5, (b) about 2 to 8 parts by weight of hydro-fluoric acid, and (c) about 2 to 40 parts by weight of acatalyst selected from the group consisting of (~) strong mineral acids selected from the group consisting of sulfuric, nitric, perchloric and hydrochloric acids and mixtures thereof;
(B) organic carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C) oxidizing agents se-lected from the group consisting of hydrogen peroxide, potas-sium chromate, potassium permanganate and chromic acid; (2) about 25 to 75 parts by weight of an organic solvent composition comprising (a) about 40 to 65 parts by weight of a normally liquid aliphatic hydrocarbon distillate boiling in the range of about 120° to 550° F., (b) about 10 to 30 parts by weight of a normally liquid aromatic hydrocarbon, (c) about 1 to 5 parts by weight of an ether of an aliphatic polyhydric alcohol, and (d) about 2 to 10 parts by weight of a lower alkyl mono-hydric alcohol; and (3) about 0.1 to 1.0 parts by weight of an anionic or nonionic surfactant, and in which the H2O/P2O5 mole ratio in the overall emulsion composition is between 2.2 and 2.8.
(B) organic carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C) oxidizing agents se-lected from the group consisting of hydrogen peroxide, potas-sium chromate, potassium permanganate and chromic acid; (2) about 25 to 75 parts by weight of an organic solvent composition comprising (a) about 40 to 65 parts by weight of a normally liquid aliphatic hydrocarbon distillate boiling in the range of about 120° to 550° F., (b) about 10 to 30 parts by weight of a normally liquid aromatic hydrocarbon, (c) about 1 to 5 parts by weight of an ether of an aliphatic polyhydric alcohol, and (d) about 2 to 10 parts by weight of a lower alkyl mono-hydric alcohol; and (3) about 0.1 to 1.0 parts by weight of an anionic or nonionic surfactant, and in which the H2O/P2O5 mole ratio in the overall emulsion composition is between 2.2 and 2.8.
17. The method defined in claim 16 wherein said strong mineral acid is hydrochloric acid.
18. The method defined in claim 16 wherein said strong mineral acid is sulfuric acid.
19. The method defined in claim 16 wherein the substantially anhydrous liquid acid composition is introduced into the formation surrounding the well bore at a pressure below the fracture pressure of the formation.
20. The method defined in claim 16 wherein the substantially anhydrous liquid acid composition is introduced into the formation surrounding the well bore at a pressure at least equal to the fracture pressure of the formation.
21. A method for increasing the permeability of a mixed subterranean geological formation penetrated by a well bore which comprises introducing into the formation a highly viscous, substantially anhydrous, liquid-acid-mixture composition, comprising: (1) about 5 to 75 parts by weight of an acid component comprising (a) about 50 to 99 parts by weight polyphosphoric acid, said polyphosphoric acid containing about 5 to 86 weight percent of the total P2O5 present as polymeric P2O5, (b) about 1 to 25 parts by weight of hydro-fluoric acid, and (c) 0 to about 50 parts by weight of a catalyst selected from the group consisting of (A) strong mineral acids selected from the group consisting of sulfuric, nitric, perchloric and hydrochloric acids and mixtures thereof; (B) organic carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C) oxidizing agents selected from the group consisting of hydrogen peroxide, potassium chromate, potassium permanganate and chromic acid; (2) about 25 to 95 parts by weight of an organic solvent component; and (3) about 0.01 to 3.0 parts by weight of an anionic or nonionic surfactant component;
and wherein the H2O/P2O5 mole ratio is from 2.1 to 3.4 in the overall acid emulsion.
and wherein the H2O/P2O5 mole ratio is from 2.1 to 3.4 in the overall acid emulsion.
22. The method defined in claim 21 wherein said organic solvent component is selected from the group consis-ting of hydrocarbon solvents, halogenated hydrocarbon solvents, polar solvents, and admixtures thereof.
23. The method defined in claim 22 wherein said organic solvent component comprises about 35 to 80 parts by weight of a normally liquid aliphatic hydrocarbon distillate boiling in the range of about 120° F. to 550° F.; about 4 to 40 parts by weight of a normally liquid aromatic hydrocarbon;
about 0.5 to 6 parts by weight of an ether of an aliphatic polyhydric alcohol; and about 1 to 12 parts by weight of a lower alkyl monohydric alcohol.
about 0.5 to 6 parts by weight of an ether of an aliphatic polyhydric alcohol; and about 1 to 12 parts by weight of a lower alkyl monohydric alcohol.
24. The method defined in claim 21 wherein the substantially anhydrous liquid acid composition is introduced into the formation surrounding the well bore at a pressure below the fracture pressure of the formation.
25. The method defined in claim 21 wherein the substantially anhydrous liquid acid composition is introduced into the formation surrounding the well bore at a pressure at least equal to the fracture pressure of the formation.
26. A method for increasing the permeability of a mixed subterranean geological formation penetrated by a wellbore which comprises introducing into the formation a highly viscous, substantially anhydrous, liquid-acid-mixture composition, comprising: (1) about 20 to 50 parts by weight of an acid component comprising (a) about 60 to 95 parts by weight polyphosphoric acid, said polyphosphoric acid containing about 40 to 75 weight percent of the total P2O5 present as poly-meric P2O5, (b) about 2 to 8 parts by weight of hydrofluoric acid, and (c) about 2 to 40 parts by weight of a catalyst selected from the group consisting of (A) strong mineral acids selected from the group consisting of sulfuric, nitric, per-chloric and hydrochloric acids and mixtures thereof; (B) or-ganic carboxylic acids selected from the group consisting of formic, acetic, chloracetic, peracetic, trichloracetic, citric, oxalic and maleic acids; and (C) oxidizing agents selected from the group consisting of hydrogen peroxide, potassium chromate, potassium permanganate and chromic acid; (2) about 50 to 80 parts by weight of an organic solvent composition comprising (a) about 40 to 65 parts by weight of a normally liquid ali-phatic hydrocarbon distillate boiling in the range of about 120° to 550° F., (b) about 10 to 30 parts by weight of a normally liquid aromatic hydrocarbon, (c) about 1 to 5 parts by weight of an ether of an aliphatic polyhydric alcohol, and (d) about 2 to 10 parts by weight of a lower alkyl monohydric alcohol; and (3) about 0.1 to 1.0 parts by weight of an anionic or nonionic surfactant, and in which the H2O/P2O5 mole ratio in the overall emulsion composition is between 2.1 and 3.4
27. The method defined in claim 26 wherein the substantially anhydrous liquid acid composition is introduced into the formation surrounding the well bore at a pressure below the fracture pressure of the formation.
28. The method defined in claim 26 wherein the substantially anhydrous liquid acid composition is introduced into the formation surrounding the well bore at a pressure at least equal to the fracture pressure of the formation.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA302,466A CA1105693A (en) | 1978-05-02 | 1978-05-02 | Non-aqueous acid emulsion composition and method for acid-treating siliceous geological formations |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA302,466A CA1105693A (en) | 1978-05-02 | 1978-05-02 | Non-aqueous acid emulsion composition and method for acid-treating siliceous geological formations |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1105693A true CA1105693A (en) | 1981-07-28 |
Family
ID=4111372
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA302,466A Expired CA1105693A (en) | 1978-05-02 | 1978-05-02 | Non-aqueous acid emulsion composition and method for acid-treating siliceous geological formations |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1105693A (en) |
-
1978
- 1978-05-02 CA CA302,466A patent/CA1105693A/en not_active Expired
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