CARBOXYLIC ACID/ACRYLAMIDOALKANE SULFONIC ACID/ST YRENE SULFONATE COPOLYMERS FOR ULTRAHIGH TEMPERATURE AND PRESSURE RETARDATION OF OIL-WELL CEMENT

BACKGROUND OF THE INVENTION

[0001] This invention relates to a unique application of a water soluble monoun- saturated carboxylic acid/acrylamidoalkane sulfonic acid/ primary copolymerizable comonomer copolymers, such as, for example, acrylic acid (AA)/2-acrylamido-2- methylpropane sulfonic acid (AMPS)/sulfonated styrene (SS) random copolymers as set retarders for oil-well cement retardation. The set retarder performs well at wide temperatures from below 200 °F up to ultra-high temperature and pressure.

[0002] Successful cementing operations are extremely crucial to reliable well completion prior to production. Cementing is considered as one of the most essential and challenging operations in wellbore construction generally due to high temperatures and pressures that can cause significant changes to the properties of the cement slurry; particularly slurries that contain multiple chemical additives. Unfortunately at high temperatures and pressures, the setting of the cement and its strength development are easily accelerated. Thus, chemical retarders are nearly ubiquitous in cement slurries to effectively control and delay the cement setting, thereby providing ample and safe pumpability time until the cementing operation is completed, and allowing zonal isolation of the wellbore from the surrounding formations. However, most chemicals quickly degrade especially at ultra-high temperatures, such as greater than 350° F, and pressures. Likewise, exposure to highly basic pH conditions and, often, high salinity environments, contribute to rapid degradation of cementing chemicals. Typically, as a unique chemical approach that is already recognized in the field, the retarding effect of the industry- known existing lignosulfonate-based or other synthetic-based retarders are intensified by addition of relatively expensive small organic molecules that are strongly cement binding like tartaric, gluconic, or citric acid. However, such addition provides extra cost to the pumping service companies or field operators, and furthermore, the incorporation of these strong adsorbate small molecules to the cement slurry design oftentimes degrades or otherwise negatively affects the fluid loss control performance of the larger molecules or polymers due to competitive binding on the surface of the cement.

[0003] A new set retarder is needed to address the foregoing problems with prior art cementing formulations.

BRIEF DESCRIPTION OF THE FIGURES

[0004] Figure 1. is a chart representing the thickening time test (TTT) results for the 16.4 ppg density cement slurry no. 5 in Table 1 of the examples at 450 °F and 10,000 psi pressure.

[0005] Figure 2. is a chart representing the thickening time test (TTT) results for the 16.4 ppg density cement slurry no. 4 in Table 2 of the examples at 190 °F and 8187 psi pressure.

SUMMARY OF THE INVENTION

[0006] The disclosed technology solves the above-mentioned problems by providing a new cement composition containing water, a hydraulic cement, and a unique set retarder.

[0007] The set retarder is a copolymer containing monomeric units derived from (a) monounsaturated carboxylic acids, salts and anhydrides thereof; (b) acrylamidoalkane sulfonic acids and salts thereof; and (c) primary copolymerizable comon- omers,

[0008] In an embodiment, the monounsaturated carboxylic acid can be a mono- carboxylic acid of from 3 to 5 carbon atoms, such as, for example, acrylic acid or methacrylic acid. The set retarder can include from about 20 to about 95 wt% of the monomeric units derived from monounsaturated carboxylic acid.

[0009] In embodiments, the acrylamidoalkane sulfonic acids can contain up to 6 carbon atoms in the alkane moiety. In embodiments, the acrylamidoalkane sulfonic acid can include 2-acrylamido-2-methylpropane sulfonic acid. In some embodiments, the set retarder can include from about 1 to about 60 wt% of the monomeric units derived from the acrylamidoalkane sulfonic acid.

[0010] In some embodiments, the primary copolymerizable comonomers can be selected from vinyl alcohol, styrene sulfonic acids, salts thereof, and mixtures thereof. In a particular embodiment, the copolymerizable comonomers can be styrene sulfonic acids or salts thereof. The set retarder can contain from about 5 to about 30 wt% of the monomeric units derived from primary copolymerizable comonomers.

[0011] In further embodiments, the set retarder can further include monomeric units derived from about 1 to about 20 wt% of one or more secondary copolymeriz- able monomers. In still further embodiments, the set retarder can have a weight average molecular weight of from about 1 ,000 to about 100,000. In embodiments, the cement composition can contain from about 0.01 to about 1 gal/sk of the set retarder. In still further embodiments, the set retarder can include 5 to 60% of the copolymer.

[0012] In some embodiments, the cement composition can contain further additives, such as, for example, fluid loss control polymers, dispersant polymers, anti-strength retrogression agents, anti-foaming agents, and the like.

[0013] Another aspect of the technology is directed to a method of cementing a subterranean zone penetrated by a wellbore. The method can include the steps of: 1) forming a pumpable set retarded cement slurry containing: hydraulic cement, water, and the set retarder described herein, 2) pumping the cement slurry into the zone by way of the wellbore; and 3) allowing the cement slurry to set therein.

DETAILED DESCRIPTION OF THE INVENTION

[0014] Various preferred features and embodiments will be described below by way of non-limiting illustration.

[0015] The technology disclosed herein includes a cement composition comprising: water, a hydraulic cement, and a set retarder.

[0016] Water typically makes up about 30 to about 60% by volume of the cementing composition. Both fresh water and/or sea water may be used in the cement composition. Typically water with low mineral content is preferred, such as tap water.

[0017] Cement typically makes up about 15 to about 50% by volume of the cementing composition. The term "hydraulic cement" means a cementing composition that sets up to a hard monolithic mass under water. Generally, any hydraulic cement may be used in the present invention. In certain embodiments, Portland cement may be used because of its low cost, availability, and general utility. In other embodiments, Portland cements of American Petroleum Institute' s ("API") Classes A, B, C, H, and/or G may be used in the invention. In other embodiments, other API Classes of cements, such as calcium aluminate and gypsum cement, may be used. In addition, mixtures or combinations of these cement components can be used. The characteristics of these cements are described in API Specification For Materials and Testing for Well Cements, API Spec 10 A, First Edition, January 1982, which is hereby incorporated by reference. In certain embodiments, the Portland cements includes classes G and/or H, but other cements which are known in this art can also be used to advantage. For low-temperature applications, aluminous cements and Portland/plaster mixtures (for deepwater wells, for example) or cement/silica mixtures (for wells where the temperature exceeds 120° C, for example) may be used, or cements obtained by mixing a Portland cement, slurry cements and/or fly ash.

[0018] The set retarder can include a copolymer comprising monomeric units derived from (a) monounsaturated carboxylic acids, salts and anhydrides thereof; (b) acrylamidoalkane sulfonic acids and salts thereof; and (c) primary copolymeriz- able comonomers,

[0019] The set retarder copolymers can be in un-neutralized or neutralized form. Such copolymers can be neutralized with a strong alkali, such as sodium hydroxide, in which instance, the hydrogen of the carboxyl group and sulfonic acid group in the copolymer will be replaced with sodium. With the use of an amine neutralizing agent, the hydrogen will be replaced with an ammonium group. Useful copolymers for purposes herein include copolymers that are un-neutralized, partially neutralized, or completely neutralized.

[0020] The set retarder copolymers contemplated herein are polymers of at least three different monomers, and include at least one monomer selected from each one of the following groups (a), (b), and (c):

(a) monounsaturated carboxylic acids of 3 to 5 carbon atoms, salts and anhydrides thereof;

(b) acrylamidoalkane sulfonic acids and salts thereof containing up to 6, preferably 1 to 4, carbon atoms in the alkane moiety; and

(c) primary copolymerizable monomers selected from vinyl alcohol, a styrene sulfonic acid or salts thereof, and mixtures thereof. It is understood that vinyl alcohol as such cannot be isolated. However, polymerized vinyl alcohol groups can be formed by hydrolysis of polymerized vinyl esters.

[0021] In addition to the above three requisite monomers, a small amount of other or secondary copolymerizable monomers can also be used as long as they do not substantially deleteriously affect performance of the copolymers. Amounts of such secondary copolymerizable monomers can generally vary up to about 20% by weight, preferably up to 10%, and more preferably 2 to 10% by weight of the final copolymer.

[0022] The copolymers suitable herein are random non-crosslinked polymers containing polymerized units of one or more of each of the monomers (a), (b), and (c), identified above, and can contain a small proportion of polymerized units of one or more of the secondary copolymerizable monomers. The copolymers have weight average molecular weight of 1,000 to 100,000, preferably 2,000 to 50,000 and more preferably 2,000 to 20,000. The molecular weight given herein is meas- ured by gel permeation chromatography.

[0023] The copolymers disclosed herein can contain from about 20 to about 95% by weight of the polymerized carboxylic acid or its salt or anhydride, preferably about 30 or about 40 to about 75%, or about 30 to about 60% by weight; about 1 to about 60% by weight of the polymerized sulfonic acid or its salt, preferably about 10 to about 50% or about 20 to about 50% by weight; about 5 to about 30% of the primary copolymerizable monomer, or about 10 to about 20% by weight. The copolymers can also include one or more polymerizable, secondary comonomers in amount of up to about 20%, preferably up to about 10%, and more preferably about 2 to 10%). In embodiments, the secondary commoner can exclude substituted acrylamides, vinyl esters, and acrylate esters.

[0024] The carboxylic acid monomers contemplated herein include monounsaturated monocarboxylic and dicarboxylic acids, salts and anhydrides thereof. Preferred in this class are monounsaturated monocarboxylic acids of 3 to 4 carbon atoms and water soluble salts thereof, particularly acrylic acid and methacrylic acid. Because of its availability, effectiveness and low price, acrylic acid is particularly preferred. Repeating units of acrylic acid, methacrylic acid, and salts thereof are represented as follows:

where R is hydrogen or methyl and X can be hydrogen, alkali metal, alkaline earth metal, or ammonium, particularly hydrogen, sodium, potassium, calcium, ammonium, and magnesium.

[0025] The repeating units of acrylamidoalkane sulfonic acids and salts thereof are defined as follows:

where R is hydrogen or methyl; X is hydrogen, ammonium, alkali metal or an alkaline earth metal, particularly hydrogen, ammonium or an alkali metal; and R ¹ and R ² are individually selected from hydrogen and alkyl groups of 1 to 4 carbon atoms. In a preferred embodiment, R is hydrogen and R ¹ and R ² are each an alkyl group of 1 to 3 carbon atoms. In this group of sulfonic acids, 2-acrylamido-2- methyl propane sulfonic acid ("AMPS™") is a commercial, readily available monomer which is especially preferred.

[0026] The primary copolymerizable monomers can be vinyl alcohol, styrene sulfonic acids and salts or mixtures thereof.

[0027] Repeating units of styrene sulfonic acids and salts thereof are defined as follows:

where R is hydrogen or a lower alkyl group of 1 to 6 carbon atoms but preferably hydrogen, and X is hydrogen, alkali metal, or alkaline earth metal, or ammonium, particularly hydrogen, ammonium or alkali metal. A particularly suitable sulfonic acid is styrene sulfonic acid where R is hydrogen and the— SO ₃ X group is at the 3 or 4 position on the phenyl ring, or a mixture thereof. The salts of styrene sulfonic acids are water-soluble. The sodium salt of styrene sulfonic acid is available commercially. [0028] The monomers can be prepared, if desired, in a conventional manner but they are commercially available and therefore, can be purchased. Polymerization of the monomers results in an essentially non-crosslinked random copolymer, the molecular weight of which can be adjusted with a little trial and error. The copoly- mer is preferably formed in a high yield ranging from about 50% to about 99% by weight of the comonomers.

[0029] The product is preferably shipped in drums as a concentrated aqueous solution containing in the range from about 5 to about 50% by weight of solids per 100 parts of solution, or, for example, from about 20% to about 50% by weight solids.

[0030] Polymerization of the monomers identified herein can be carried out in a mutual solvent for both, such as in a lower alkanol of about 1 to 6 carbon atoms, or in water, with an effective amount of a free radical initiator sufficient to produce the desired composition within an acceptable period of time. The monomeric acids can be used as such or can be in a partially or a completely neutralized from prior to polymerization.

[0031] The reaction is conveniently carried out in water as the only reaction medium at a temperature in the range of about 30° to about 130° C, usually at atmospheric pressure. The concentration of the copolymer formed may range from about 5% to about 60% by weight, based on total solids, which solution can be shipped directly.

[0032] The copolymer may also be formed in an acyclic ketone, such as acetone, in an alkanol, in water, or mixtures thereof. If, for example, the copolymer is formed in an organic solvent, or a mixture of an organic solvent and water, the copolymer is converted from the organic solvent solution to a water solution. Typically, the organic solvent is stripped from the solution with steam or distilled off with subsequent additions of water and repetition of distillation to remove the solvent, followed by the addition of water and a neutralizing agent such as caustic solution, ammonia, a hydrazine, or a low-boiling primary, secondary or tertiary aliphatic amine. The copolymers containing vinyl alcohol are formed by subjecting the initially formed vinyl acetate copolymers to hydrolysis conditions whereby the polymerized vinyl acetate groups are converted to polymerized vinyl alcohol groups. In a typical preparation, aqueous sodium hydroxide solution is added to a preformed copolymer containing vinyl acetate groups. The amount of sodium hydroxide used is typically one mol of sodium hydroxide for each mol of polymerized vinyl acetate plus one mol of sodium hydroxide for each mol of polymerized carboxylic and sulfonic acid present.

[0033] The final aqueous solution of polymer salt is preferably in the range of about pH 2 to about pH 8, with a total solids content of about 5 to about 60% by weight of polymer in water.

[0034] The copolymers formed may have weight average molecular weight in the range of about 1,000 to about 100,000, preferably 2,000 to 50,000, and more preferably about 2,000 to 20,000, as determined by gel permeation chromatography.

[0035] In a typical polymerization process, a glass lined or stainless steel jacketed reactor is charged with predetermined amounts of monomers along with solvent and the polymerization catalyst under a nitrogen blanket, and the reaction mixture allowed to exotherm under controlled temperature conditions maintained by a heat- transfer fluid in the jacket of the reactor. The pressure under which the reaction occurs is not critical, it being convenient to carry it out under atmospheric pressure.

[0036] In a typical cement composition, the set retarder can be included at from about 0.01 to about 1 gallon of set retarder per each 94 pound sack of hydrau- lie cement ("gal/sk"), which works out to about 0.28 to about 28% by volume of the set retarder to cement.

[0037] Depending on the specifications regarding the conditions for use, the cementing compositions can also be optimized by adding additives which are common to the majority of cementing compositions, such as suspension agents, dispersing agents, anti-foaming agents, expansion agents (for example magnesium oxide or a mixture of magnesium and calcium oxides), line particles, fluid loss control agents, gas migration control agents, retarders or setting accelerators

[0038] The cement composition can also include at least one fluid loss control polymer. A typical fluid loss control agent can include, for example, at least one of a copolymer of 2-acrylamido-2-methylpropane sulfonic acid and N,N dimethyl aery 1 amide; a polyvinyl alcohol; a hydroxyethyl cellulose; a carboxy methyl hydroxyl ethyl cellulose; or combinations thereof. Fluid loss control polymer can be include at about 0.1 % to about 3 % by weight of cement ("BWOC").

[0039] The cement composition can also include from about 0.1 % to 1% BWOC of at least one dispersant polymer, such as, for example, a sulfonated naphthalene formaldehyde polycondensate; an acetone formaldehyde polyconden- sate; a melamine formaldehyde polycondensate; a polycarboxylate; or combinations thereof.

[0040] The cement composition can further include an anti-strength retrogression agent, such as, for example, a crystalline silica material. Typically a cement composition can include from about 30% to about 60% BWOC of a crystalline silica having mesh sizes of 100 mesh; 200 mesh; 325 mesh; or combinations thereof.

[0041] Anti-foaming agents, such as silicon-based defoamers; alcohol-based defoamers; or combinations thereof, may also be employed in the cement composi- tion. Anti-foaming agents typically can be included from about 0.01 to about 0.05 gal/sk.

[0042] The amount of each chemical component described is presented exclusive of any solvent or diluent oil, which may be customarily present in the commercial material, that is, on an active chemical basis, unless otherwise indicated. However, unless otherwise indicated, each chemical or composition referred to herein should be interpreted as being a commercial grade material which may contain the isomers, byproducts, derivatives, and other such materials which are normally understood to be present in the commercial grade.

[0043] It is known that some of the materials described above may interact in the final formulation, so that the components of the final formulation may be different from those that are initially added. For instance, metal ions can migrate to other acidic or anionic sites of other molecules. The products formed thereby, including the products formed upon employing the composition of the present invention in its intended use, may not be susceptible of easy description. Nevertheless, all such modifications and reaction products are included within the scope of the present invention; the present invention encompasses the composition prepared by admixing the components described above. [0044] As used herein, the term "about" means that a value of a given quantity is within ±20% of the stated value. In other embodiments, the value is within ±15% of the stated value. In other embodiments, the value is within ±10% of the stated value. In other embodiments, the value is within ±5% of the stated value. In other embodiments, the value is within ±2.5% of the stated value. In other embodiments, the value is within ±1% of the stated value.

[0045] Additionally, as used herein, the term "substantially" means that a value of a given quantity is within ±10% of the stated value. In other embodiments, the value is within ±5% of the stated value. In other embodiments, the value is within ±2.5%) of the stated value. In other embodiments, the value is within ±1% of the stated value.

[0046] The cement composition can be employed in a method of cementing a subterranean zone penetrated by a wellbore. In carrying out the method, the cement composition is prepared by admixing in a suitable vessel the hydraulic cement, water, set retarder, and any other optional additives that may be desired. The resulting cement composition can then be pumped into a well bore or conduit disposed therein to a subterranean zone wherein the cement composition is to be placed.

[0047] The method can include the steps of: 1) forming a pumpable set retarded cement slurry comprising hydraulic cement, water, and the set retarder as described herein, 2) pumping said cement slurry into said zone by way of said wellbore; and 3) allowing the cement slurry to set therein.

[0048] The set retarder described herein can provide: (i) delay the setting of oil- well cement at ultra-high temperature, such as, for example, temperatures of greater than about 350, and even greater than 425° F, and high pressures, such as greater than about 10,000 psi, without the addition of extra chemical intensifiers; (ii) provide excellent thermal stability while minimizing the expected significant thermal thinning of cement slurry when subjected to ultra-high temperature and pressure, therefore avoiding the need of an extra high temperature suspending aid to combat thermal thinning; and (in) maintain compatibility with other cement additives, such as industry-known commonly-used fluid loss control additive. [0049] The foregoing may be better understood with reference to the following examples.

EXAMPLES

[0050] Slurry preparation and description of testing method:

[0051] The cement slurries reported in Table 1 & 2 were prepared by following the American Petroleum Institute (API) recommended practice (RP) 10B mixing procedure using a standard constant blender speed mixer from Chandler (Model 3065). Briefly, after adding the defoamer and mixing for 15 seconds at 4000 rpm speed in the reactive water, the new liquid retarder was quickly added to the solu- tion and was mixed for about 15 to 30 seconds at 4000 pm, the dry blend of cement and other chemical additives were added to the mixture in the stainless steel blender cup. The final slurry were mixed for 15 seconds at 4000 rpm and then for another 35 seconds at 12,000 rpm rotational speed.

[0052] After mixing, the rheology of the slurry was determined quickly at room temperature (~67-70°F) using the Ofite Model 900 viscometer, and the RPM 300- 200- 100-60-30-6-3 readings were recorded including the 10 sec/10 min static gel values. While the pumpability time of the prepared slurry was measured using the Ofite high pressure-high temperature (HPHT) consistometer set-up at about 10,000 psi and varying temperatures as indicated in Table 1 & 2. Finally, the compressive strength of cement was measured via ultrasonic cement analyzer (UCA) in-situ or standard crashed testing method, which was accomplished by applying a load directly to the cured cement at controlled rate of 4000 lb _f per minute. Both set-ups were also obtained from Ofite. Test results are summarized in Table 1 & 2.

[0053] Summarized in Table 1 are the cement slurry designs and high tempera- ture performance testing results including rheology at RT, thickening time and compressive strengths measurements. Briefly, the slurry formulations (1) to (5) contain Class H cement from Texas Lehigh or Class G cement of either Dyckerhoff or UCN, a standard copolymer synthetic fluid loss control additive (product named CFL 160M), a typical antifoaming agent, silica sand of either 100 mesh, 200 mesh or a combination of both, varying dosage of the set retarder as described herein at the levels as indicated in the Table 1, and reactive water. A standard cement polymer dispersant can be added optionally to the cement slurry and weighting agent hematite for high density cement slurry.

Table 1: Summary of cement slurry designs and high temperature performance testing results at 250 °F to 450 °F and -10, 000 psi.

[0054] Additional slurry preparation and testing:

[0055] Summarized in Table 2 are the cement slurry designs and low-to-mid temperature performance testing results including room temperature rheology, thickening time and compressive strengths measurements. Briefly, the slurry formulations (1) to (5) contain Class H cement from Texas Lehigh, a standard copolymer synthetic fluid loss control additive (product name CFL 1 17), a typical antifoaming agent, varying dosage of the set retarder as described herein at the levels as indicated in the Table 2, and reactive water.

Table 2: Summary of cement slurry designs and low-to-mid temperature perfor- mance testing results at 150 °F to 225 °F and between 8,000-10,000 psi.

[0056] As used herein, the transitional term "comprising," which is synonymous with "including," "containing," or "characterized by," is inclusive or open-ended and does not exclude additional, un-recited elements or method steps. However, in each recitation of "comprising" herein, it is intended that the term also encompass, as alternative embodiments, the phrases "consisting essentially of and "consisting of," where "consisting of excludes any element or step not specified and "consisting essentially of permits the inclusion of additional un-recited elements or steps that do not materially affect the essential or basic and novel characteristics of the composition or method under consideration.

[0057] While certain representative embodiments and details have been shown for the purpose of illustrating the subj ect invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. In this regard, the scope of the invention is to be limited only by the following claims.