CA1199783A

CA1199783A - Method for recovering oil from an underground deposit

Info

Publication number: CA1199783A
Application number: CA000422855A
Authority: CA
Inventors: Dieter Balzer; Kurt Kosswig
Original assignee: Chemische Werke Huels AG
Current assignee: Huels AG; Evonik Operations GmbH
Priority date: 1982-03-06
Filing date: 1983-03-04
Publication date: 1986-01-28
Also published as: HU187049B; DE3208206A1; EP0088206A2; EP0088206A3; YU44283A; EP0088206B1; DE3361572D1; ATE17151T1; NO830761L

Abstract

ABSTRACT
A method for recovering largely emulsion-free oil from an underground deposit of medium or high salinity by injecting, into an injection bore-hole, a 0.1 to 30% solution or dispersion, in formation- or flood-water, of carboxymethylated oxethylates of the formula:
R - (OCH2CH2)n - OCH2 - COOM, wherein R signifies a linear or branched aliphatic residue with 6 to 20 carbon atoms or an alkyl- or dialkyl-aromatic residue with 3 to 16 carbon atoms in the alkyl group, M signifies an alkali or alkaline-earth metal ion or ammonium ion, n lies between 1 and 3 and the degree of carboxymethylation between 10 and 90%, the surfactant selected being such that the phase-inversion temperature of the crude-oil/formation- or flood-water/surfactant/possible additives system lies at 0 to 10°C above the temperature of the deposit. The method sharply reduces pressure gradients developing during transportation of the oil through the formation.

Description

~9~3 In recovering oil from oil-bearing deposits, it is generally possible -to ex-trac-t only a fraction of the oil originally present by primary recovery methods, whereby the oil reaches the surface as a result of the natural pressure in the deposit. In secondary recovery, water is usually injected into one or more injection bore-holes, the oil is driven to one or more production bore-holes, and is thus brought to the surface. As a secondary measure, this so-called water-flooding is relatively inexpensive and is therefore used frequently.
In many cases, however, it leads only to a slight increase in the amount of oil extracted.
Further expulsion of the oil, which is more costly but urgen-tly necessary in view of the present shortage of oil, is achieved by -tertiary measures. These include processes whereby either the viscosity of the oil is lowered and/or the viscosity of the flood-wa-ter is increased and/or the inter-facial tension between the water and the oil is reduced.
Most of these processes can be classified either as solu-tion- or mixture-flooding, thermal oil-recovery processes, surfactant- or polymer-flood-ing, or combinations of several of these.
Thermal recovery processes involve the injecting of steam or hot water or underground combustion. Solution or mixture processes consis-t of injecting a solvent for the mineral oil into the deposit. The solvent may be a gas and/or a liquid.
Surfactant-flooding processes - depending upon surfactan-t concentration, surfac-tant type and additives, may be divided into surfactant-assisted water-flooding, conventional surfactant-flooding ("low-tension flooding"), micellar flooding and emulsion-flooding - and are based mainly upon a sharp reduction in interfacial tension between oil and flood-water. In certain cases, however, especial-1~L99~33 ly in the presence of higher concentrations of surfactant, water-in-oil disper-sions occur with distinctly higher viscosities than oil, in which case it is the purpose of surfactant-flooding to reduce mobility-conditionsJ thus increasing oil displacement efficiency. Straight polymer-flooding is based mainly upon the effect mentioned above of more favourable mobility-conditions between the oil and the after-flooded water.
The present invention is based upon a method for recovering oil by surfactant-flooding. The main mobilizing surfactants have hitherto been organic sulphonates~ such as alkyl-, alkylaryl- or petroleum-sulphonates, but these have a very low tolerance for deposit-water salinity. Even salt concentrations o~
1 000 ppm create problems, the sensitivity of these surfactants to alkaline-earth ions being particularly pronounced and the upper critical limit of concen-tration being assumed to be about 500 ppm ~United States Patent 4 110 228).
When these surfactants are used in the presence of high concentrations of saltJ
precipitates are formed which may block the formation. HoweverJ since deposit-water is often more highly saline (up to 250 000 ppm in northern GermanyJ for example) methods have been sought whichJ while retaining the satis~actory oil-mobilizing properties of organic sulphonatesJ may also be used in more highly saline deposit- systems. When mixed with co-surfactantsJ such as alcohols or non-ionic surfactantsJ organic sulphonates have proved to be less sensitive to electrolytes, but this has usually impaired the oil-mobilizing effect.
In contrast to this group of substancesJ alkyl- and alkylarylpolyglycol-ether-sulphates or carboxymethylated alkyl- or alkylaryl-oxethylates show good compatibility even with extremely high salinities (e.g. 250 000 ppm) in deposit-waters. Since the oil-mobilizing effect of these surfactants is satisfactory ~H.J. NEUMANNJ DGMK REPORTSJ Report 164 (1978) J D. BALZER and K. KOSSWIG, Tenside

2 -, ~ , . . .

~991~7~33 Detergents 16, 256 (1979)), and since they may be produced simply and economi-cally, these classes of substances are highly suitable for displacing oil in medium and highly saline deposit systems (10 000 to 250 000 ppm total salt content).
However, in the course of nurnberous investigations into residual oil-mobilizing in model formations with carboxymethylated oxethyla-tes as surfactants, it has been found that transportation of the layer of oil through the formation is accompanied by a sharp increase in pressure. Even in the case of highly permeable artificial formations, pressure-gradients of up to 40 bars/m have been found. When transferred to the field, this leads to pressures far in excess of the petrostatic pressure, and this would exclude the use of these surfactants for tertiary mineral-oil recovery. Reference is also made to pressure-gradien-ts of similar orders of magnitude in the relevant literature (C. MARX, ~. MURTADA, M. BURKOWSKY, Erdoel Erdgas Zeitschrift 93, 303 (1977)). It is believed that these high pressure differences arise from the formation of emulsion-zones which are supposed to be limited to -the area of the flooding front. In investigations, however, we observed no local limitation of pressure-gradients. Furthermore, since crude-oil emulsions, stabilized by carboxymethylated oxethylates, are intrinsically viscous, the high pressure-differences cannot be lowered a-t will, even by lowering the flooding velocity. Surfactant-flooding with carboxymethyl-ated oxethylates must therefore be expected to produce uncontrollably high pres-sure gradients in the oil field.
There was therefore a need to discover a surfactant-flooding procedure, using carboxymethyla-ted oxethylates with their good oil-mobilizing properties, which does not result in high pressure-gradients. A reduction in pressure gradi-ents is rendered possible in that a sharply delayed surfactant breakthrough is sought by suitable adaptation of the amo~m-t of surfactant to the deposit. How-~ - 3 -97~33 , ~ , ever, this procedure assumes homogeneous formations and, although these occur in artificial beds of sand, they are scarcely to be expected in actual deposits.
It was therefore scarcely possible to solve the probelm in this way.
Surprisingly enough the problem was solved by abandoning a convention-al working hypothesis. This hypothesis, which is also advanced in the relevant literature, assumes that effective residual-oil extraction is possible only by meeting the conditions required for the presence of a w/o emulsion as far as possible throughout the entire flooding operation. ~U. LEPPER, Erdoel Erdgas Zeitschrift 92, 426 (1976)). According to D. BALZER and ~. KOSSWIG, Tenside Detergents 16, 256 (1976~, this means that the phase-inversion temperature (PIT~, of the original crude-oil and formation- or flood-water system, if flooding is not carried out with formation-water, surfactant and possible additives~ must be clearly below the temperature of the deposit, in fact up to 15C. In the case of flooding tests carried out under these conditions in model formations, highly effective oil-extraction was usually observed, and it was found that the crude oil could be flooded out quite predominantly free of emulsion. Nevertheless, this procedure very often leads to high pressure-gradients.
Now it has been found that the pressure-gradients ma~ be sharply re-duced, with satisfactory oil-extraction, by the method of the present invention.
This was extremely surprising since the relevant temperature-range is the characteristic range for an o/w emulsion.
According to the present invention there is provided a method for re-covering oil from an underground deposit of average or high salinity by inject-ing into an injection bore-hole, a 0.1 to 30% solution or dispersion, in forma-tion- or flood-water, of a carboxymethylated oxethylate as a surfactant of the formula:

'71~3 ( 2 2)n 2 COOM, wherein R is a linear or branched aliphatic resldue with 6 -to 20 carbon a-toms or an alkyl- or dialkyl- aromatic residue wi-th 3 to 16 carbon atoms in the alkyl group, M signifies an alkali or alkaline-earth metal ion or ammonium ion, and the degree of carboxymethyla-tion lies between 10 and 90%, the surfactant selec-ted being such that the phase-inversion temperature of the crude-oil/formation -or flood-water/surfactant/additive (where present) system is at -the temperatureof the deposit or at 10 C thereabove, characterized in that n lies between 1 and 3.
If a surEactant is selected which, with regard to the deposit system, has a PIT 11 C or more above the temperature of the deposit temperature and is thus within the characteristic range of an o/w emulsion, mobilization of the residual oil is not very effective and the oil appears quite predominantly as an emulsion.
The PIT itself is determined by measurement of electrical conductivity.
To this end an emulsion is produced consisting of crude oil, formation-wa-ter from the relevant deposit or flood-water (phase ratio 1 : 1 and 1 : 2), the surfactant (2% in relation to the aqueous phase), and possibly additives, and the elec-trical conductivity of this emulsion is measured as a function of tem-pera-ture. At the PIT an o/w emulsion changes into a w/o emulsion or vice-versa and the electrical conductivity rises or falls abruptly.
To be accurate, this is a temperature-range of only a few degrees Cel-sius, the PIT being the temperature at which the electrical conductivity reaches a mean value between the upper (o/w) and the lower (w/o) level.
The present invention relates to -the~use of carboxymethylated oxe-thyl-ates as oil-mobilizing surfactants. According to German Patent 24 18 444, these compounds may be produced by reacting oxe-thylates of the formula:

,' ~L95~'7~3 R - (O - CH - CH ) OH
with a salt of chloroacetic acid in the presence of alkali-hydroxide or alkaline-earth hydroxide, but other production processes are also suitable. In this case, R signifies a saturated or unsaturated, straight-chain or branched alkyl residue with 6 to 20, preferably 8 to 16 C-atoms, or an alkylaryl residue with 3 to 6 C-atoms in the alkyl residue. Not only can n assume values of 3 -to 30, as stated in our Patent Application P 31 34 530.1, but n, which indicates the degree of oxethyla-tion, may also be between 1 and 3 - as we have in the mean-while discovered unexpectedly from numerous tests. The cation may be sodium, potassium, lithium, ammonium, calcium or magnesium. The oxethylates, from which the carboxymethylates are derived, may be based on the following alcohols and phenols, for example: hexyl-alcohol, octyl-alcohol, nonyl-alcohol, decyl-alcohol, undecyl-, lauryl-, tri-decyl-, myristil-, palmityl- and stearyl-alcohol, but also unsa-turated alcohols, for example oleyl-alcohol. In this con-nection, the alkyl chain may be normal or branched. It is particularly expedi-ent to use commercially available mixtures of these alcohols. The following may be used as alkyl-phenols for example: propyl-phenol, bu-tyl-phenol, hexyl-phenol, octyl-phenyl, nonyl-phenol, decyl-phenol, undecyl-phenol, dodecyl-phenol, tri-decyl-phenol, tetradecyl-phenol, hexadecyl-phenol, dibutyl-phenol, dihexyl-phenol, etc. The alkyl chain may be normal or branched. More par-ticularly, commercially available mixtures of such alkyl-phenols may be used.
Oxethylation may be carried out in the presence of catalytic quantities of alkali-hydroxide with 1 to < 3 moles of ethylene-oxide. The resu]-ting mix-tures have almos-t a Poisson distribution.
Depending upon how they are produced, carboxymethylated oxe-thylates contain considerable quantities of unreacted oxethylate. Thus the formula:

~3L9~3 R - (OC~12- C~12)n ~ OCH2 - COOM
indicates a mixture having different quantities of unreacted oxethylate. This makes it possible to define a degree of carboxymethylation. It has been found that mixtures having a degree of carboxymethylation of between 10 and 90%, pre-ferably between 30 and 90%, are capable of displacing the oil effectively.
Particularly effective are mixtures having a 50 to 90% degree of carboxymethyla-tion. ~le term percentage always means percentage by weight in this connection.
The described mixtures of anionic and non-ionic surfactant, called carboxymethylated oxethylates, are soluble, or at least easily dispersible, in usual deposit-waters, and substantially no precipitation is observed.
The procedure is as follows: wlth a knowledge of the temperature, or temperature-range, of the deposit, the crude oil, the formation-water or flood-water and possibly the gas of the deposit, and an apparently suitable car-boxymet~ylate~oxethylate of the above formula, is used for a PIT measurement by way of orientation. This measurement should be repeated, if necessary, with other surfactants of this class and possibly additives.
The carboxymethylated oxethylate is tailored to the result of this measurement and the oil-mobilizing effectiveness thereof may be verified by means of one or more preliminary tests carried out in a bed of sand as a model-formation or on original or model drill-cores.
Sodium-salts of carboxymethylated oxethylates, produced by reacting oxethylates with chloroacetic acid in the presence of a caustic soda solution, offer several reference points for "molecular architecture" with a view to achieving the desired phase-inversion temperature in a specific system:

:, ~

~9783 R - (OCII2CH2)n - OH + ClC~I2COOH _ NaCl - H2O

R - CCH2cH2)n - CH2COONa . . , R n Reaction Variable ~ Variable The salts of carboxymethylated oxethylates consist of three variable structural elements: the hydrophobic residue R, the oxethylate chain, and the carboxymethyl group, the proportion of which in the product-mixture obtained may may be varied within wide limits by controlling the reaction between the initial oxethylate and chloroacetic acid. Starting materials for hydrophobic residue R
may be, for example~ linear and branched (fatty) alcohols, also alkyl-phenols with any desired alkyl residues. The effect of the alkyl group or alkylaryl group upon the phase-inversion temperature has already been indicated ~D. BALZER
and K. KOSSWIG, loc. cit.). The principle, according to which strengthening the hydrophobic property of the surfactant ion reduces the PIT, whereas an increase in the hydrophilic property increases it, applies in this case.
Figure 1 shows the dependency of the phase-inversion temperature in a specific system having an oxethylation eficiency of _.
Use was made of crude oil ~, formation water F and about 70% of car-boxymethylated Alfol 121& oxethylates of different degrees of oxethylation. The surfactant concentration was 2% and the o/w phase-ratio as 1 : 2. A report was also produced on the effect of the degree of carboxymethyla~ion upon the PIT
~D. BALZER and K. KOSSWIG, loc, cit.). Figure 1, and the said investigations, show the variability of the deposit conditions offered to us by the class of carboxymethylated oxe~hylates which are actually mixtures of ionic and non-ionic surfactants.

~IL1991~33 Furthermore, the volume of surfactant solution to be injected, the concentration thereof and possible additives, and also the type and aMount of polymer solution controlling mobility may be optimized, if necessary, by means oE model flooding-tests. Based upon the results of these preliminary tests, surfactant solution is introduced into the deposit with the aid of injector-pumps. In this connection, the surfactant solution may be injected continuously or in the form of a slug, i.e. a narrowly limited volume amounting to 0.05 to 4.0 PV (=multiple of the pore-volume of the deposit). The size of the slug is governed mainly by the concentration of the surfactant solution and economics.
It is desirable for the surfactant-flooding to be preceded by water-flooding, for which the formation-water produced or other water may be used.
The size of the water-slug is between 0.01 and 4, preferably between 0.05 and 1.0 PV. A polymer slug is injected into the deposit after the surfactant slug, not only for controlling mobility but also to protect the surfacta~t solution from incoming formation- or flood-water. To this end a polymer or mixture of polymers is dissolved in the formation- or flood-water at a concentration such as that the viscosity is between 4 and 6 times that of the oil. In the case of deposits of medium or high salinity (1 to 28%), the most suitable polymers are biopolymers, such as polysaccharides or cellulose derivatives which are still of adequate viscosity in the presence of the increased salt concentration and also produce no precipitation.
In order that the viscosity of ~he surfactan* solution may be better adapted to the oil, or in order ~o reduce surfactant- and possibly polymer-retention, it may be desirable to add to the surfactant, or to the polymer slug, alcohols or glycols as co-surfactants. Examples of suitable co-surfactants in this case are: i-propanol, i-butanol, n-butanol, t-amylalcohol, 2-ethylhexanol, _ ~ _ 97~33 butyl-diglycol, butyl-triglycol.
In the case of formation - and flood-water rela-tively low in alkaline-earth ions, it may be found desirable to add soluble alkaline-earth salts to the surfactant solution, and also to the pre- and post-flood water. These addi-tives must be taken into account in adapting the surfactant to -the deposi-t, i.e. in measuring the PIT.
The injection of the polymer solution is preferably followed by normal water-flooding as a propellent. This is continued as long as oil is recovered economically.
The following examples are intended to explain the method according to the invention.
Example 1 For the purpose of producing an artificial formation, a thermostatic-ally controlled high-pressure pipe 70 cm in length and 5 cm in diameter, equipped with temperature-measuring means and a pressure gauge, and adapted to be closed at both ends by threaded caps fitted with a capillary inlet and a pressure-maintaining-valve outlet, was filled with rounded-edge quartz sand. The sand was -then saturated with formation-water F by means of a high-pressure me-tering pump, the desired temperature being adjusted by means of a thermostat. The permeability of the bed of sand was determined wi-th the aid of a pressure-trans-mitter. This was followed by saturation with crude oil, the con-ten-t of absorbed water being measured simultaneously. Water-flooding was now initiated at a flooding velocity of about 2.5 m/d. After flooding-in about 1.5 PV of forma-tion-water (1 PV about 750 ml), producing a 98 to 100% degree of dilution, the sur-factant was added as a slug. rrhis was followed by 3.0 PV of formation-water as propellent. Surfactant-flooding, and subsequent after-flooding with formation-water, were carried l9~783 out at a flooding velocity of about 1 m/d. The formati.on temperature was 68C, its pressure 60 bars, the porosity of the artificial formation about 45%, its permeability about 1 000 mD, and its absorbed-water content about 25%.
Formation-water F contained about 23.5 g of NaCl, 0.75 g of KCl, 1.1 g of CaC12~ 5 g of MgC12, 4 g Na2S0~ and 0.2 g of NallC03 per litre.
A paraffin-base oil of 37 API was used as the crude oil F. The con-tents of paraffin, naphthenes and aromatics amounted to about 61, 18 and 21%
respectively.
The surfactant solution used was a 1.5 PV of 2% dispersion of carboxy-methylated C14-fatty-alcohol-oxethylate with 2.4 moles of ethylene-vxide/mole9 in formation-water. The degree of carboxymethylation was about 70%, the PIT of the relevant crude-oil emulsion 73.5C. Water-flooding produced 69% oil-extrac-tion. With a further 1.4 PV after the start of surfactant-flooding, this was increased by 19% to a total oil-extraction of 88%. In this case dilution dropped to about 60%. During transportation of the layer of oil produced by the surfactant, an average pressure-gradient of about 1.6 bars/m was measured.
Example 2 (comparison example).
With conditions, substances and method-steps practically identical to F.xample 1~ with a test temperature of 80C ~the PIT was 73.5C as in Example 1), this comparison example was carried out. Water-flooding produced 72% oil-ex-traction which, with a further 1.3 PV after the start of the surfactant-flooding, increased to a total oil-extraction of 94%, but the average pressure-gradient measured was 18 bars/m.
When transferred to the field, such a pressure-gradient would lead to pressures far above the petrostatic pressure, thus making it impossible to use the surfactants in tertiary oil-extraction.

'`:, ~lg9~7~3 Example 3 _ _ The model Eorma-ti.on for this example was a horizontally mounted, cylindrical core of Bentheim sandstone about 8 cm in diamenter and about 50 cm in length, embedded in epoxy resin, and with its end closed off by metal flanges sealed with 0-rings. Temperature-control was by means of a water-bath fi-tted with a thermostat. After the formation had been moistened with formation water B, after determination of the pore-volt~e (1 PV about 620 ml) and the permeabil-ity (about 1 300 mD), the core was saturated with crude oil B. The procedure was otherwise as in the preceding examples, except that the flooding veloci-ty was only half as high and no polymer was flooded-in after -the surfac-tant slug as a mobility buffer.
The formation water B contained about 63.6 g of NaCl, 0.4 g of KCl, 15.1 g of CaC12, 3.1 g of MgC12, 0.4 g of SrC12 and 0.4 g of BaC12 per litre.
The crude oil used was a paraffin-base oil of 40 API. The contents of paraffins, naphthenes and aromatics amounted to about 75, 12 and 13% respec-tively.
The surfactant solution used consisted of 2 PV of a 1% dispersion of carboxymethylated oxe-thylates of a fatty-alcohol mixture with 12 to 18 carbon atoms and 2.7 moles o~ ethylene-oxide per mole, which also contained 0.2~6 of isobutanol. The degree of carboxymethylation of the surfactan-t amounted to about 75%. The PIT of the relevant crude-oil emulsion, at 48 C in rela-tion to the 43 C -temperature of the model formation, lies within the range according to the invention. Wa-ter-flooding produced 50% oil-extraction, increasing to 80%
by surfactan-t-flooding and subsequent water-propelling after 2.0 PV. An average pressure-gradient of 0.3 bars/m was measured.

~ ~ - 12 -97~3 Example 4 (comparison example).
This Example was carried out using conditions, substances and mekhod-steps practically identical to Example 3, but using 2.5 PV of a 1% solution of carboxymethylated oxethylate of a fatty-alcohol mixture with 12 to 18 carbon atoms and 2.5 moles of ethylene-oxide per mole as the surfactant, to which 0.2%
of isobutanol was also added. The PIT of the crude-oil emulsion, at 42C, was lower in this case than the temperature of the model formation ~43C). Water-flooding produced 53% oil-extraction which was increased to 90% with the aid of surfactant-flooding.
During transportation of the oil-layer, a pressure-gradient of 7 bars/m was developed which could scarcely be controlled by deposit-technology in field-tests at normal depths.
Example 5 This test was conducted using conditions, substances and method-steps practically identical to Example 1, but using a carboxymethylated oxethylate of a fatty-alcohol mixture with 12 to 18 carbon atoms and 1.5 moles of ethylene-oxide per mole (PIT 46C) and a deposit-*emperature of 41C. Water-flooding produced 74% oil-extraction, which was increased to 99% by the action of the surfactant. In this example according to the invention, an easily controlled pressure-gradient of 1.2 bars/m was produced during surfactant flooding.

.~,

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for recovering oil from an underground deposit of average or high salinity by injecting into an injection bore-hole, a 0.1 to 30% solution or dispersion, in formation- or flood-water, of a carboxymethylated oxethylate as a surfactant of the formula:
R - (OCH2CH2)n - OCH2 - COOM, wherein R is a linear or branched aliphatic residue with 6 to 20 carbon atoms or an alkyl- or dialkyl- aromatic residue with 3 to 16 carbon atoms in the alkyl group, M signifies an alkali or alkaline-earth metal ion or ammonium ion, and the degree of carboxymethylation lies between 10 and 90%, the surfactant selected being such that the phase-inversion temperature of the crude-oil/formation- or flood-water/surfactant/additives (where present) system is at the temperature of the deposit or at 10°C thereabove, characterized in that n lies between 1 and 3.

2. A method according to claim 1, wherein an additive is added to the crude-oil/formation- or flood-water/surfactant system.

3. A method according to claim 1, wherein the phase-inversion temperature of the crude-oil/formation- or flood-water/surfactant/additive system lies at 1 to 10°C above the temperature of the deposit.

4. A method according to claim 1, 2 or 3, wherein a monovalent, bivalent or trivalent alcohol is added to the surfactant solution or dispersion.

5. A method according to claim 1, 2 or 3, wherein an alkaline-earth salt soluble in formation-water is added to the crude-oil/formation- or flood water/
surfactant system.

6. A method according to claim 1, 2 or 3, wherein 0.01 to 4 PV of forma-tion- or flood-water is injected into the deposit prior to the injection of the surfactant solution.

7. A method according to claim 1, 2 or 3, wherein 0.01 to 4 PV of forma-tion- or flood-water is injected into the deposit after the injection of the surfactant solution.

8. A method according to claim 1, 2 or 3, wherein 0.01 to 4 PV of forma-tion- or flood-water is injected into the deposit after the injection of the surfactant solution and the formation- or flood-water contains a viscosity-increasing polymer.

9. A method according to claim 1, wherein the surfactant has a degree of carboxymethylation of between 30 and 90%.