GB1572174A - Hydrothermal cement and a method of cementing a string of pipe in a bore hole - Google Patents

Description

(54) HYDROTHERMAL CEMENT AND A METHOD OF CEMENTING A STRING OF PIPE IN A BORE HOLE (71) We, SOUTHWEST RESEARCEX INS- TITUTE, a Corporation organised under the Laws of the State of Texas, United States of America, of 8500 Culebra Road, San Antonio, State of Texas 78284, United States of America, do hereby declare the invention for which we pray that a patent mqv be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement.

Portland cement is prepared conventionally by grinding limestone and clay and/or other materials to a fine powder, mixing thoroughly, and burning the mixture in a long rotary kiln. At the hot zone of the kiln, where the temperature approaches 3000"F., the mixture is sintered and fused together into nodules called "clinker" which is ground to a fine powder. Substantial fuel is required to serve the energy demand for this low cost, high volume conventional cement material, and, as in all energy consuming industries, fuel shortages curtail cement production. Hence, a need exists for low energy consuming cements in building materials.

The possibility of fossil fuel shortages and accompanying demand for high energy fuels has spurred efforts to recover geothermal energy as well as petroleum gas deposits trapped in very deep cavities and to liberate these reserves. Nuclear devices have been proposed as fracturing methods to stimulate production of high yields. However, the combination of inherentlv high subterranean temperature and the added thermal influx from nuclear stimulation poses a serious threat to the stability of cements used to reinforce the casing and walls of the wells and to secure the casings to wells in desired con fiurations for attachment to above-ground piping and valve assemblies.The high temperature gradients that define the thermal profile of these wells constitute a source of variable stress between cement and steel cas in a , The high coefficient of thermal expansion of metal compared to concrete (in the range of 5-50 to 1) can induce adhesive failure if the cement bond is not satisfactory Conventional Portland cements rapidly lose adhesive strength at elevated temperatures (i.e., 300OF. and higher) and possess only marginal strength under optimum temp era- ture conditions. For example, the shear bond of Portland cement to "Re Bar" (conventional steel reinforcing rods) averages 500 psi while the shear bond of Portland cements to conventional polished steel is only 50 psi.

The added stress of thermal degradation would render a Portland cement useless in regard to adhesion in wells of the nature described above. Consequently, the need exists for a high strength cement exhibiting high shear bond and adhesion properties for the uses described.

In the drilling of conventional oil and gas wells, casing is cemented not only to secure the casing in the bore hole but also to prevent communication betweeen water, oil and gas-producing zones within the well. The typical procedure for cementing wells of this nature involves mixing Portland cement compositions at the well site and pumping the cement downwardly through casing and then outwardly and upward through a well between the casing and the wall of the bore hole. Ordinarily, a plurality of high pressure pumps and piping systems are required to guard against pump failure. In the event of pump failure, the cement sets almost immediately and hardens, thereafter requiring expensive drilling operations to salvage the well.Thus, it would be advantageous to provide a method of cementing a string of pipe in a bore hole whereby the cement will not set, harden or cure except by passage of time or by exposure of the cement to given temperature conditions that exist within the well or both. The present invention is directed to such method which eliminates the necessity of equipping cementing systems with duplicate pumps and related appara- tus and which virtually eliminates the hazard of the cement setting before the desired time which might lead to loss of the well.

Applicant is aware of prior art in the field including U.S. Patents Nos. 1,318,076; 1,852,672; 2,042,011; 2,238,930; 2,279,262; 2,302,913; 2,502,418; 2,586,814; 2,665,996; 2,682,092; 2,701,209; 2,805,719; 2,883,723; 2,895,838; 3,146,828; 3,180,748; 3,208,523; 3,244,230; 3,253,664; 3,317,643; 3,326,269; 3,736,163, 3,374,834; 3,435,899 and 3,581,825, and an article entitled "Effect of Jet Perforating on Bond Strength of Cement" by W. K. Godrey, Journal of Petroleum Technology, pages 1301-14, November 1968. Of the foregoing, Applicant deems the most pertinent to be Patents Nos. 1,852,672; 2,665,996; 3,146,828; 3,326,269, and 3,736,163.

The No. 1,825,672 patent is directed to pozzolanic activity of active clay minerals with alkaline earth oxides such as calcium and magnesium. The No. 3,326,269 patent teaches the fixation of free silica by the high temperature firing of mixtures of colloidal silica and the hydroxide of various collodial polyvalent metals. Neither patent is concerned with reactions or products subject of the present invention.

The No. 3,146,828 paten teaches the use of heat to generate a rigidized mineral mass of highly porous silicate and silica of moderately low strength (1546 psi in the highest case). It teaches the use of the material to form a consolidating barrier of a permeable structure within the formation surrounding the well bore, the purpose of which is to aid the fracturing of formations and assure a continuous recovery of fluids. The bonding or cementitious material is defined as being sodium silicate to which is added a zinc oxide stabilizing agent in the amount of 0.5 to 2.0 parts by weight to reduce the water sensitivity.The patent disclaims any benefits of greater amounts of zinc oxide (column 6, lines 54 to 59) and describes a process wherein sodium silicate solutions are dehvdrated thermally at such a rate (indicated bv the minimum temperature shown as 175"F.) that a porous film results which serves as a binder. It has been found in practice that the cement of the 3146828 patent is a water-vapour sensitive product, one which is stable at low humidity but softens and degrades at 1750 at 100% relative humidity within 24 hours of exposure. When formulations such as those described in column 5, lines 6 through 75, and column 6, lines 1 through 60. are prepared and cured under closed autoclave conditions at 175OF.

and 100% relative humidity for five days, a plaslic non-rieid product results rimless the sample is allowed to dehvdrate. Where evaporation is permitted or induced, the cement does harden. If such a formulation is charged into a well whose formation permits water vapor transfer from the cement, a hardening will result. If the formation is tight or if the cement is cast between nonporous steel casings as is often done, the cement may fail to set firmly and may not achieve the porosity claimed by the inventor as critical to the invention (column 5, lines 6-16). Thus, the 3146828 patent formula tions have definite limitations.

The No. 2,665,996 patent describes a hydrated calcium silicate-crystalline product that is unstable at temperatures above 450OF. and reacts at room temperature as well as elevated temperatures. Furthermore, the 2665996 patent product does not have the property of adhesion to steel. By comparison, the composition of the present invention is a hydrothermally reacted product, inert or unreactive at room temp era- ture while reactive at higher temperatures with the consequent benefits of remaining mobile or pumpable for long periods of time at less than the threshold of activation temperatures.Furthermore, the product of the present invention cures to a heat-resistant solid with great adhesive strength to steel and resistance to acids and is an amorphous, polymeric, non-crystalline and nonhvdrous solid as compared with that of the 2665996 patent.

Patent No. 3,736,163 discloses a lightweight insulative product consisting of mineral wool type fibers bonded toether with calcium silicates moieties which become partially mineralized during use. The product of the 3736163 patent is cured in any autoclave at 200 psi staem (400"F.) for three hours, then dried and has negligible adhesion to metal and is a crystalline hydrate of dicalcium silicates that are initially dehydrated before released for use. The product of the 3736163 patent process survives temperatures of not greater than 1200"F. because of stress relief by way of microfractures and microstrain dissipated by the fiber fillers.

When the same compositions (875 pounds lime and 750 pounds of uncalcined diatomaceous earth, 150 pounds of anhydrous sodium silicate, 7 pounds of sugar, 60 pounds of nodulated mineral wool; 60 pounds of sulfite pulp fibers and 50 pounds of clay in 720 gallons of water) is autoclaved as described in the 3736163 patent, a product which is a mixture of crystalline calcium silicates is obtained as confirmed by x-ray analysis.

By comparison, the vastly different composition of the present invention contains, for example, minimal amounts of water as compared with the 3736163 patent. Minimal water in the product of the present invention allows reaction to form polymers of non-crystalline and non-hydrous solids that provide resistance to high temnerature thereby dispensing with the necessity of fibers as i nthe 3736163 patent for the purpose of dissipating stresses.

The present invention relates to a family of cements characterized by hydrothermally initiated curing, the cement mixture retaining mobility or pumpability at less than the threshold activation temperature that initiates the cure. Objectives of the invention are to provide such a cement of high strength and curable by a substantially greater than conventional passage of time and by exposure to elevated temperature or both; a method for cementing a strip of pipe in a bore hole through use of such hydrothermal cement composition; a cement composition eminently suitable and stable when cured for use in high temperature wells driven into the earth; and to minimize energy or fuel requirements in preparation of cement compositions.

A hydrothermal cement is defined herein as one that achieves a high degree of mechanical strength under somewhat higher than standard atmospheric temperature and pressure conditions, by in situ formation of polyvalent silicate salts from reacting silica and metal oxides, hydroxides or salts of low solubility. The reaction of silica and metal oxides or hydroxides and formation of polyvalent silicate salts involves a mechanism requiring heat and moisture to promote chemical combination of the basic constituents. Polyvalent metal oxides, hvdroxides or salts that are capable of combination with silica gel or silicates in an aqueous medium are induced to form the respective silicates by application of heat to acqueous slurries of these materials with silica flour and alkali metal silicates.The latter serve as reagents which react with the metal oxides to form silicates and alkali metal oxides or hydroxide. The caustic by-product is free to react with silica from the sand and silica flour of the formulation, and the resultant materials generate a reactive sodium silicate which repeats the cycle until either the polyvalent metal is exhausted, the water evaporates or all of the silica is depleted or otherwise unavailable.

As used herein, the terms "initiation temerature" and "activation temperature" both refer to the minimum temperature at which the foregoing described reactions begin and below which the materials simply are in physical mixture. Advantarreouslv. the initiation temperatures of the family of hydrothermal cements of the present invention vary according to the type of polyvalent metal ions and the ratio of SiO/NaoO in the sodium silicate used. Consequently, set tina of the cements of the present invention does not occur with normal passage of time until the cement is exposed to a temnerature hih enough to cause activation of the reactions.This feature of the formulation according to the present invention uniquely adapts the cement compositions for use in cementing casing in well bore holes and the like.

The cement has high strength and is also well suited for may other uses.

It is therefore an object of the present intion to provide a family of cements characterized as susceptible of hydrothermally initiated cure, the cementitious mixture remaining mobile or pumpable for long periods of time at less than the threshold of activation temperatures.

A further object of the present invention is the provision of a family of cements comprising high molecular weight, inorganic polymers from the reaction of polyvalent metals with silica under conditions of moisture and elevated temperatures.

A further object of the present invention is the provision of hydrothermal cements, each comprising a mixture of a polyvalent metal salt, water and a silica source that can be hydrated by time and temperature such that the silica is available for combination with the polyvalent metal salt upon application of heat.

A still further object of the present invention is the provision of a method of cementing pipe or casing within a well bore wherein a hydrothermal cement of the foregoing composition is prepared and pumped into the annular space between the pipe and walls of the bore hole and then allowed to set due to temperature conditions in the bore hole or by passage of time or both.

Yet a further object of the present invention is the provision of such a method that reduces the necessity of duplicative pumping and circulating equipment inasmuch as failure of such equipment does not in and of itself result in setting of the cements in a bore hole.

A still further object of the present invention is the provision of such a method whereby the cement may be mixed offsite, is transposed to the site and may be held for long periods of time relative to Portland cement before and before setting occurs.

A further object of this invention is the provision of a water-reducing reagent which minimizes the water required to obtain workability of a slurry containing cement forming reactants according to the present invention and hence optimizes the physical mechanical and chemical properties of the cured cement.

A still further object of this invention is the provision of a coating, binder or building product of high mechanical strength, chemical resistance, abrasion resistance and resistance to intense and prolonged heating and heat cycling.

Other and further obiects, features and advantages will be apparant in the following description of presently preferred embodi ments of the invention, given for the purpose of disclosure.

The cement composition of the present invention is formulated by blending dry components including the polyvalent metal ion source such as a polyvalent metal oxide, hydroxide, salt of low solubility, or mixtures thereof together with a silica source such as clay, silica flour, silica sand and sodium silicates or equivalent substitutes. A water-reducing reagent comprising a spray-dried hydrated sodium silicate powder is used to reduce the amount of water needed to fluidize the system. Preferably, the blending and mixing step is conducted in a closed container substantially free of air and water to prevent lumping because of moisture and to prevent carbonation of silicates by carbon dioxide in the air. The blend of dry materials is then slurried with the required (as will be explained) minimum amounts of water.Prolonged delay in adding water, especially in a humid environment, allows the powdered mixture to cake and subsequently makes it more difficult to disperse and hydrate. The consistency of the water/solid mixture undergoes a dramatic transition within ten minutes following the addition of water whereby a marked drop in viscosity converts an otherwise damp cake to a thin, pumpable slurry. This occurs as a consequence of the dissolution of the hydrated sodium silicate. The slurry viscosity can be varied drastically by adding relatively small (1 to 2% by weight) increments of water.

The polyvalent metal ion is a reactant and ingredient of the cement composition according to the present invention is a polyvalent metal oxide, hydroxide, low solubility salt or mixture thereof. The polyvalent metal oxides, hydroxides, and salts that may be used include the oxides of zinc, magnesium, iron, aluminum, manganese, titanium, zirconium, vanadium and hafnium; the hydroxide of aluminum; the carbonates of zinc and magnesium; and the phosphates of calcium, magnesium and aluminum.

Examples of formulations making use of various of the polyvalent metal ions sources are as follows wherein particle size is less than the stated mesh, standard ASTM Ell analysis, unless otherwise indicated.

Example 1 Parts by Weight Range Preferred Sand (2060 mesh) 4060 50 Silica flour (325 mesh) 20--40 25 2.4/1 ratio SiO2/Na2O spray dried Hydrated Sodium Silicate Powder (325 mesh) 5-15 10 3.22/1 ratio SiO2/Na20 Anhydrous Sodium Silicate Powder (325 mesh) 5-15 10 Flyash W25 0 Zinc oxide ( < 1 micron) 5-15 7 Water 1520* 17* * Per hundred parts by weight of total solids ("phpts").

Using the preferred formulation, the cement begins to act at an activation temperature of 150OF. and sets firmly in 24 hours at this temperature. At 200OF. a hard cure is achieved in less than 24 hours. In about one week, the cement attains a compressive strength of 4000 psi at 2000F. and a shear bond of 1300 psi. The cured cement resists temperatures to 2000OF. without adversely affecting its physical strength. In this example as in all subsequent examples, the procedure followed for determining compressive strength is ASTM C109-54T while the test for determing shear bond or adhesive strength is one used conventionally in the petroleum industry. It consists of measuring the force per unit area required to displace or disrupt the bond between a metal cylinder and a concrete cylinder.

Example 2 Parts by Weight Range Preferred Sand 40-60 50 Silica flour 2040 25 2.4/1 ratio SiO2/Na2O spray dried Hydrated Sodium Silicate Powder 5-15 10 3.22/1 ratio SiO2/Na20 Anhydrous Sodium Silicate Powder 5-15 10 Aluminum Hydroxide (reagent grade preferred from NaAl2Oa + Nh+OH 5-20 7 Water 1520 phpts 17 phpts This formulation is indefinitely stable below 145 F. but rapidly begins to thicken at 200 F. No true setting is observed below 165 F. and the preferred activation temperature for finite rates of observable change in setting characteristic is 200 F. A cure of two weeks at 200 F. results in a compressive strength of over 2000 psi.Over 3000 psi, compressive strength is obtained at 2000F.

in four weeks. Approximately 4000 psi is obtainable in five to six weeks at this temperature. At 300"F., strengths on the order of 4700 psi are obtainable in two weeks. The cement has a shear bond strength of 1300 psi and withstands temperatures of up to 1000 F. adversely affecting its physical strength.

Example 3 Parts by Weight Range Preferred Sand 40-60 50 Silica flour 2040 25 3.22/1 ratio SiO2/Na2O Anhydrous Sodium Silicate Powder 5-15 10 2.4/1 ratio SiO,/Na,O spray dried Hydrated Sodium Silicate Powder 5-15 10 Aluminum Hydroxide (commercial grade from NaA203 + steam) 5-15 7 Water 15-20 phpts 17 phpts Activation temperatures on the order of 225 F. result in a strength of 3700 psi in about 72 hours.

Example 4 Parts by Weight Range Preferred Sand 40-60 50 Silica flour 20--40 25 3.22/1 ratio SiO2/Na2O Anhydrous Sodium Silicate Powder 5-15 10 2.4/1 ratio SiO2/Na2O spray dried Hydrated Sodium Silicate Powder 5-15 10 Al203 Calcined or Dehydrated 5-15 7 Water 15-20 phpts 17 phpts The lowest observed practical activation temperature for this formulation is 2250. A temperature of 300OF. is preferred since this results in curing being substantially completed in a period of less than two weeks. A strength of 3700 psi is obtainable in about 72 hours with an activation temperature of 300OF.

Example 5 Parts by Weight Range Preferred Sand 40-60 50 Silica flour 20--40 25 7.5/1 ratio SiO2/Na2O Anhydrous Sodium Silicate Powder 5-15 10 2.4/1 ratio SiO2/Na2O spray dried Hydrated Sodium Silicate Powder 5-15 7 Zinc oxide 5-15 7 Water 15-20 phpts 17 phpts The substitution of 7.5/1 ratio (SiO2/NaO) sodium silicate for 3.22/1 ratio reduces the activation temperature from 1500F to 135OF. The compressive strength of this recipe after seven days at 135OF. is 3600 psi.If the more alkaline sodium silicates are used (ratio of 3/1 and less, i.e., 2/1 or 2.4/1 alone), no setting is observed in five days at 1500 F. The 2.4/1 ratio silicate serves as a fluidizer or viscosity-improving additive during the handling of the cement mixture. The more alkaline silicates require higher temperatures and/or longer times to react and rigidize.

Example 6 The formulations of Examples 1-5 may be used excluding or replacing the hydratable sodium silicates with sodium hydroxide in parts by weigth of 1 to 10, 5 parts by weigth being preferred. This substitution may be used without appreciable effect on the chemical or physical properties as indicated in each example. The kinetics of each formulation will be affected to some degree by the substitution.

As previously stated, formulations of the cement composition according to the present invention may be made using still other polyvalent metal oxides, hydroxides or salts.

For example, the oxides of magnesium, iron aluminium, magnesese, titanium, zirconium, vanadium and hafnium, the carbonates of zinc and magnesium and the phosphates of magnesium and aluminum may be used.

Concentrations of any of these substitutes for the polyvalent metal compounds of Examples 1-6 should be proportioned to the relative equivalent weights of these compounds compared to the equivalent weights of the polyvalent metal compounds cited in these examples.

The inclusion of sodium silicate as the hydratable silica source in these formulations is not a mandatory requirement but is preferred. Sodium silicate is produced by high energy-consuming processes, and in order to mimimize inclusion of materials of this nature, the silicate may be generated in the cement system by the reaction of sodium hydroxide with available silica. Various clays, sands and ground sand are suitable sources of silica for this purpose.

Any washed sand used conventionally in Portland cement, concrete and mortar formulations may be used in the cement in the cement formulations of the present invention. The sand has little effect on strength of the resultant cement products but affects cost, fluidity and bulking factor of the cement mixture.

Silica flour likewise should be of low clay content and the proportions used dictate fluidity and strength of the set material versus time. That is, the more silica flour used, the less fluid is the cement mixture before setting but the greater strength after setting in given periods of time.

With regard to silicates used, anhydrous silicate is used partly as a matter of convenience to tie up free water that results after all reactions are concluded. The more sili cqte of this nature used, the faster the cure.

The ratio of SiO2/Na2O in the sodium silicate is a reaction rate controlling factor.

The more siliceous grades (higher SiO2 ratios) react more rapidly and at lower temperatures than the more alkaline grades.

With respect to the alkali metal silicate hydrate powders, produced by spray drying of alkali metal silicate solutions of a narrow ranp;e of SiO2 /Na2O ratios, the powder sur prisinaly have been found to produce a high degree of fluidity in slurries with very small quantities of water. This latter feature constitutes one source of the unique physical, chemical and mechanical properties described herein. Water, essential to the chemical curing of most inoranic cement systems is quantitatively critical to the final product properties. Any excess or residual water in a cured product evaporates leaving pores and sites of vulnerability to free-thaw damage, infusion of foreign matter, reduced strength, etc.Trapped water or waters of hydration common to all hydraulic cements like Portland limit the heat resistance of the products. Since the cement of the present invention employs only 15 to 20% moisture, a higher degree of impermeability and greater mechanical strength may be achieved than is possible otherwise. The addition of water induces a partial solution of the alkali metal hydrates powders which upon dissolution fluidizes the system by release of a colloided electrolyte that imposes a partial charge on the slurry inducing a high degree of lubricity where equivalent slurries without the electrolyte would appear as slightly dampened powders. This liquification does not occur immediately upon addition of water and its blending with the dry powders.After about two minutes with little or no agitation, the dampened mass suddenly liquifies to a highly fluid state which can be readily poured, pumped and extruded. This slurry can subsequently be rendered thixotropic by addition of any suitable bentonite product.

With respect to the polyvalent metal compounds used in each formulation, the concentration of the particular metal compound should be proportional to all others according to equivalent weights. Without the polyvalent metal compounds, all other constituents would remain relatively inactive.

With respect to water used in the formulations of the present invention, any clear water may be used as is used in conventional concrete and mortar formulations. The amount of water affects fluidity and final strength. That is, the more used, the greater the fluidity of the mixture before setting but the lower the strength after set. Water is essential to promote reaction of silicate polymers and salts of the polyvalent metals.

Flyash and other pozzolanic materials may be used as fillers to perform the same function that sand performs as outlined above.

Concretes may be prepared by adding gravel and rock to mortar formulations of thes present invention. Concretes prepared accordingly exhibit very low water absorption when cured, even after exposure to several hundred degree temperature. Consequently, the formulations of the present invention are uniquely suited for use in formulation building materials that are or may all be "low energy produced" in that no cal- cining or kiln processing is required to prepare the raw materials for the concrete. especially when the aforementioned sodium hydroxide-silica reaction is employed to generate sodium silicate.

As may be seen from the examples, formulation of cement compositions according to the present invention by using different polyvalent metal compounds results in diffe- rent formulations having varying activation temperatures. For example, the formulation of Example 1 has an activation of 1500 F.

and the formulation of Example 3 has an activation temperature of 225OF. As a result, it will now be apparent that a formulation may be selected having a specific activation temperature such that the formulation is uniquely adaptable for use in temperature environments wherein the cement remains mobile until subjected to a temperature high enough to activate setting and curing reactions. For example, various formulations of cement according to the present invention may be used in cementing pipe or casing within bore holes of wells drilled in the earth. Since temperature at a given point within a bore hole depends on depth of the well, the formulation used to cement the casing may be selected by determining temperature of the bore hole and comparing that temperature to the activated temperature of the various formulations of the present invention.For example, if the downhole temperature is approximately l5û F., the formulation of Example 1 may be used whereby the bore hole temperature of 15û F.

causes the cement to set when finally placed in the wall. However, below such temperature the cement remains mobile or pumpable for long periods of time relative to conventional Portland cements. In the same way, other cements from among formulations of the present invention may be selected for use in bore holes having different temp era- tures, necessitating use of formulations having corresponding activation temperatures.

In using cement formulations of the present invention for cementing casing wells, the cement is prepared as explained elsewhere herein. The cement may be prepared at the well site although, advantageously, it may be prepared at points remote from the well site and shipped to the site without setting. Minimal agitation is required while holding the cement prior to use, the agitatation serving merely to prevent stratification of the material. This feature of formulations according to the present invention is extremely significant when considering the mixing and transportation problems of conventional Portland cements.

The cement is then pumped in the annular space between the string of pipe or casing and the walls of the bore hole as in conventional processes. However, the need for standby pumping equipment is not as critical since the cement of the present invention will not set for several hours after being subjected to the activation temperature, thereby allowing adequate time for repair or replacement of the pumping equipment. Once in place in the well, pumping stops and the cement is allowed to set due to temperature of the bore hole or by passage of time or XI!h; In this connection, cement formula- tions of the present invention having activa tion temperatures substantially lower than temperature of the bore hole may be used although shorter periods of time than those described in the examples will be experi enced for setting and curing to take place.

In any event, the ultimate strengths obtain able by the present cement are at least as great as those obtained by conventional Portland cements while the shear bond strength exceed those of Portland cement as indicated in the examples. Consequently, the cement formulations of the present inven tion provide adhesive strengths that greatly exceed those of conventional Portland cements and thereby uniquely adapt formu lations of the present invention for use in high temperature bore holes such as geo thermal wells and the like.

Still other uses of formulations according to the present invention may be made de pending on temperature requirements and length of time available for setting and cur ing. It will now be apparent to those skilled in the art that formulations of the invention may be used for a variety of applications.

WHAT WE CLAIM IS: 1. A cement composition comprising (a) a polyvalent metal ion source, (b) water (c) a hydratable silica source wherein the silica becomes available for chemical combination with the polyvalent metal ion source (a) upon application of heat, and (d) spray dried hydrated silicate powder, as a water reducing reagent to reduce the amount of water needed to fluidize the composition.

2. A cement composition, as claimed in claim 1, wherein the polyvalent metal ion source is a polyvalent metal oxide, hy droxide, salt of low solubility or mixture thereof.

3. The cement composition of claim 2, wherein the polyvalent metal ion source (a) includes one or more oxides of zinc, mag- nesium, iron, aluminium, magnganese, tita nium, zirconium, vanadium or hafnium, the hydroxide of aluminium, the carbonates of zinc or magnesium, and the phosphates of magnesium or aluminium, and combinations thereof.

4. The cement composition of any one of claims 1 to 3, wherein the silica source is clay, silica flour, or silica sand or any combination thereof.

5. A cement composition, as claimed in any one of the preceding claims, characteri zed as a pumpable slurry susceptible to a hy rothermally initiated cure, and comprising (a) from 5 to 15 parts by weight of the polyvalent metal ion source, (b) from 15 to 20 parts by weight of the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (25)

**WARNING** start of CLMS field may overlap end of DESC **. temperatures. For example, the formulation of Example 1 has an activation of 1500 F. and the formulation of Example 3 has an activation temperature of 225OF. As a result, it will now be apparent that a formulation may be selected having a specific activation temperature such that the formulation is uniquely adaptable for use in temperature environments wherein the cement remains mobile until subjected to a temperature high enough to activate setting and curing reactions. For example, various formulations of cement according to the present invention may be used in cementing pipe or casing within bore holes of wells drilled in the earth. Since temperature at a given point within a bore hole depends on depth of the well, the formulation used to cement the casing may be selected by determining temperature of the bore hole and comparing that temperature to the activated temperature of the various formulations of the present invention.For example, if the downhole temperature is approximately l5û F., the formulation of Example 1 may be used whereby the bore hole temperature of 15û F. causes the cement to set when finally placed in the wall. However, below such temperature the cement remains mobile or pumpable for long periods of time relative to conventional Portland cements. In the same way, other cements from among formulations of the present invention may be selected for use in bore holes having different temp era- tures, necessitating use of formulations having corresponding activation temperatures. In using cement formulations of the present invention for cementing casing wells, the cement is prepared as explained elsewhere herein. The cement may be prepared at the well site although, advantageously, it may be prepared at points remote from the well site and shipped to the site without setting. Minimal agitation is required while holding the cement prior to use, the agitatation serving merely to prevent stratification of the material. This feature of formulations according to the present invention is extremely significant when considering the mixing and transportation problems of conventional Portland cements. The cement is then pumped in the annular space between the string of pipe or casing and the walls of the bore hole as in conventional processes. However, the need for standby pumping equipment is not as critical since the cement of the present invention will not set for several hours after being subjected to the activation temperature, thereby allowing adequate time for repair or replacement of the pumping equipment. Once in place in the well, pumping stops and the cement is allowed to set due to temperature of the bore hole or by passage of time or XI!h; In this connection, cement formula- tions of the present invention having activa tion temperatures substantially lower than temperature of the bore hole may be used although shorter periods of time than those described in the examples will be experi enced for setting and curing to take place. In any event, the ultimate strengths obtain able by the present cement are at least as great as those obtained by conventional Portland cements while the shear bond strength exceed those of Portland cement as indicated in the examples. Consequently, the cement formulations of the present inven tion provide adhesive strengths that greatly exceed those of conventional Portland cements and thereby uniquely adapt formu lations of the present invention for use in high temperature bore holes such as geo thermal wells and the like. Still other uses of formulations according to the present invention may be made de pending on temperature requirements and length of time available for setting and cur ing. It will now be apparent to those skilled in the art that formulations of the invention may be used for a variety of applications. WHAT WE CLAIM IS:

1. A cement composition comprising (a) a polyvalent metal ion source, (b) water (c) a hydratable silica source wherein the silica becomes available for chemical combination with the polyvalent metal ion source (a) upon application of heat, and (d) spray dried hydrated silicate powder, as a water reducing reagent to reduce the amount of water needed to fluidize the composition.

2. A cement composition, as claimed in claim 1, wherein the polyvalent metal ion source is a polyvalent metal oxide, hy droxide, salt of low solubility or mixture thereof.

3. The cement composition of claim 2, wherein the polyvalent metal ion source (a) includes one or more oxides of zinc, mag- nesium, iron, aluminium, magnganese, tita nium, zirconium, vanadium or hafnium, the hydroxide of aluminium, the carbonates of zinc or magnesium, and the phosphates of magnesium or aluminium, and combinations thereof.

4. The cement composition of any one of claims 1 to 3, wherein the silica source is clay, silica flour, or silica sand or any combination thereof.

5. A cement composition, as claimed in any one of the preceding claims, characteri zed as a pumpable slurry susceptible to a hy rothermally initiated cure, and comprising (a) from 5 to 15 parts by weight of the polyvalent metal ion source, (b) from 15 to 20 parts by weight of the

water per hundred parts by weight of total solids, (c) from 60 to 100 parts by weight of the silica source, and (d) from 5 to 15 parts by weight of the spray dried hydrated sodium silicate powder.

6. The cement composition of claim 5 wherein (a) the polyvalent metal ion source con sists of about 7 parts by weight of zinc oxide, (b) water is present in the amount of about 17 parts by weight per hun dred parts by weight of total solids, (c) the silica source includes (i) about 50 parts by weight sand, (ii) about 25 parts by weight silica flour.

(iii) about 10 parts by weight anhydrous sodium silicate powder, and (d) the spray dried hydrated sodium sili cate powder is present in the amount of about 10 parts by weight.

7. The cement composition of either of claims 5 to including additionally up to 25 parts bv weight flyash.

8. The cement composition of claim 5 wherein (a) the polvvalent metal ion source con sists of about 7 parts by weight of reagent grade aluminium hydroxide, (b) water is present in the amount of about 17 parts by weight per hundred parts by weight of total solids, and (c) the silica source includes, (i) about 50 parts by weight sand, (ii) about 25 parts by weight silica flour, (iii) about 10 parts by weight anhydrous sodium silicate powders and (d) the water spray dried hydrated sodium silicate powder is present in the amount of about 10 parts by weight

9.The cement composition of claim 5 wherein (a) the polyvalent metal ion source con sists of about 7 parts bv weight of commercial grade aluminium hy droxide, (b) water is present in the amount of about 17 parts bv weight and (c) the silica source includes, (i) about 50 parts by weight sand, (ii) about 25 parts by weight silica flour, (iii) about 10 parts by weight anhydrous sodium silicate powder, and (d) the spray dried hydrated sodium sili cate powder is present in the amount of about 10 parts by weight.

10. The cement composition of claim 5 wherein (a) the polyvalent metal ion source con sists of about 7 parts by weight alu minium oxide, (b) the water is present in the amount of about 17 parts by weight per hun dred parts by weight of total solids, (c) the silica source includes, (i) about 50 parts by weight sand, (ii) about 25 parts by weight silica flour, (iii) about 10 parts by weight anhydrous sodium silicate powder, and (d) the spray dried hydrated sodium sili cate powder is present in- the amount of about 10 parts by weight.

11. A cement composition as claimed in claim 1 characterized as a upmpable slurry susceptible to a hydrothermally initiated cure and comprising (a) from 5 to 15 parts by weight of the polyvalent metal ion source, (b) from 15 to 20 parts by weight of the water per hundred parts by weight of total solids, and wherein the silica source comprises (i) from 40 to 60 parts by weight sand, (ii) from 20 to- 40 parts by weight of silica flour, and wherein the sodium silicate is present in the amount of about 10 parts by weight.

12. A method of cementing a string of pipe in a bore hole, comprising the steps of (1) preparing a cement composition com prising (a) a polyvalent metal oxide, hydroxide, salt or mixture thereof, (b) water (c) a hydratable silica source wherein the silica is available for chemical combination with the polyvalent metal ion source (a) upon- application of heat, and (d) spray dried hydrated sodium silicate powder as a water reducing reagent to reduce the amount of water needed to fluidize the composition (2) pumping the cement composition-into an annular space between the string of pipe and the wall of the bore hole, and (3) allowing the cement to set due to the temperature of the bore hole and by passage of time.

13. The method of claim 12 wherein, in the cement composition prepared in step (1) the polyvalent metal oxide, hydroxide, salt or mixture thereof includes oxides of zinc, magnesium, iron, aluminium, maganese titanium, zirconium, vanadium or hafnium, the hydroxide of aluminium, the carbonates of zinc or magnesium and the phosphates of magnesium or aluminium, and combinations thereof.

14. The method of claim 12 wherein, in the cement composition prepared in step (1), the silica source is a clay, silica flour or silica sand, or any combination thereof.

15. A method of cementing a string of pipe in a bore hole, comprising the steps of, (1) preparing a cement composition as a pumpable slurry susceptible of a hy drothermally initiated cure, compri sing (a) from 5 to 15 parts by weight of a polyvalent metal ion source, (b) from 15 to 20 parts by weight of water per hundred parts by weight of total solids, (c) from 60 to 100 parts by weight of a hydratable silica source wherein the silica becomes available for chemical combination with the polyvalent metal ion source (a) upon application of heat, and (d) from 5 to 15 parts by weight of spray dried hydrated silicate powder as a water reducing reagent to reduce the amount of water needed to fluidize the composition (2) pumping the cement composition into an annular space between the string of pipe and the wall of the bore hole, and (3) allowing the cement to set due to the temperature of the bore hole and by passage of time.

16. The method of claim 15 wherein, (a) the polyvalent metal ion source con sists of about 7 parts by weight of zinc oxide (b) the water is present in the amount of about 17 parts by weight per hundred parts by weight of total solids, (c) the silica source includes, (i) about 50 parts by weight sand, (ii) about 25 parts by weight silica flour, (iii) about 10 parts by weight anhydrous sodium silicate powder, and (d) the spray dried hydrated sodium sili cate powder is present in an amount of about 10 parts by weight.

17. The method of claim 15 including, additionally, up to 25 parts by weight flyash.

18. The method of claim 15 wherein (a) the polyvalent metal ion source con sists of about 7 parts by weight of reagent grade aluminium hydroxide, (b) the water is present in the amount of about 17 parts by weight per hundred parts by weight of total solids, (c) the silica source includes, (i) about 50 parts by weight sand, (ii) about 25 parts by weight silica flour, (iii) about 10 parts by weight anhydrous sodium silicate powder, and (d) the spray dried hydrated sodium sili cate powder is present in an amount of about 10 parts by weight.

19. The method of claim 15 wherein, (a) the polyvalent metal ion source con sists of about 10 parts by weight of commercial grade aluminium hy droxide, (b) the water is present in the amount of about 17 parts by weight per hundred parts by weight of total solids, (c) the silica source includes, (i) about 50 parts by weight sand, (ii) about 25 parts by weight silica flour, (iii) about 10 parts by weight anhydrous sodium silicate powder, and (d) the spray dried hydrated sodium sili cate powder is present in an amount of about 10 parts by weight.

20. The method of claim 15 wherein (a) the polyvalent metal ion source con sists of about 7 parts by weight alu minium oxide, (b) the water is present in the amount of about 17 parts by weight per hundred parts by weight of total solids, (c) the silica source includes, (i) about 50 parts by weight sand, (ii) about 25 parts by weight silica flour, (iii) about 10 parts by weight anhydrous sodium silicate powder, and (d) the spray dried hydrated sodium sili cate powder is present in an amount of about 10 parts by weight.

21. The method of claim 15 wherein the cement composition comprises: (a) from 5 to 15 parts by weight of a polyvalent metal ion source, (b) from 15 to 20 parts by weight of water per hundred parts by weight of total solids, (c) a hydratable silica source wherein the silica becomes available for chemical combination with the polyvalent metal salt (a) upon application of heat, the silica source comprising, (i) from 40 to 60 parts by weight of sand, (ii) from 20 to 40 parts by weight of silica flour, and (d) from 1 to 10 parts by weight of sodium silicate.

22. A cement composition as claimed in claim 1 substantially as described herein.

23. A cement composition substantially as set forth in any one of the Examples herein.

24. A method of cementing a string of pipe in a bore hole as claimed in claim 12 substantially as described herein.

25. A method of cementing a string of pipe in a bore hole utilising the cement composition substantially as set forth in any one of the Examples herein.