# Patent

## Title
Expoxy acid based biodegradable set retarder for a cement composition

## Abstract

A cement composition or method of using the cement composition in a subterranean formation, the composition having: (A) cement; (B) water; and (C) a polymer, wherein the polymer: (i) comprises a monomer or monomers selected from the group consisting of epoxysuccinic acid, a substituted epoxysuccinic acid, and an alkali metal salt, alkaline earth metal salt, or ammonium salt of any of the foregoing, and any combination of any of the foregoing; (ii) has the following characteristics: (a) is water soluble; and (b) is biodegradable; and (iii) is capable of providing: (a) a thickening time of at least 2 hours for a test composition at a temperature of 190° F. and a pressure of 5,160 psi; and (b) an initial setting time of less than 24 hours for the test composition at a temperature of 217° F. and a pressure of 3,000 psi.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This is a divisional of U.S. application Ser. No. 12/711,945 filed Feb. 24, 2010.


FIELD OF THE INVENTION
The invention is directed to a cement composition for use in a subterranean formation and a method for cementing a subterranean formation. In certain embodiments, the subterranean formation is penetrated by an oil or gas well.
SUMMARY
According to an embodiment, a cement composition comprises: (A) cement; (B) water; and (C) a polymer, wherein the polymer: (i) comprises a monomer or monomers selected from the group consisting of epoxysuccinic acid, a substituted epoxysuccinic acid, and an alkali metal salt, alkaline earth metal salt, or ammonium salt of any of the foregoing, and any combination of any of the foregoing; (ii) has the following characteristics: (a) is water soluble; and (b) is biodegradable; and (iii) is capable of providing: (a) a thickening time of at least 2 hours for a test composition at a temperature of 190° F. and a pressure of 5,160 psi; and (b) an initial setting time of less than 24 hours for the test composition at a temperature of 217° F. and a pressure of 3,000 psi, wherein the test composition consists of 860 grams of Class-H Portland cement, 325 grams of deionized water, and 0.4% by weight of the cement of the polymer.
According to another embodiment, a method for cementing in a subterranean formation comprises the steps of: (A) introducing the cement composition into the subterranean formation; and (B) allowing the cement composition to set after introduction into the subterranean formation.



BRIEF DESCRIPTION OF THE DRAWING
The features and advantages of the inventions will be more readily appreciated when considered in conjunction with the accompanying drawing. The accompanying drawing is incorporated into the specification to help illustrate examples of certain embodiments. The drawing is not to be construed as limiting the invention.
The experiments for the data contained in the drawing were performed on a cement composition, having a density of 16.4 pounds per gallon (ppg), containing: 5.48 gallons of deionized water; Class-H cement; SSA-2TM strength stabilizer at a concentration of 35% by weight of the cement (bwc); HALAD®344 fluid loss additive at a concentration of 0.5% bwc; and polyepoxysuccinic acid (PESA). The drawing includes the following figures:
FIG. 1 is a graph of thickening time in minutes (min) versus temperature in Fahrenheit (° F.) for the cement composition at a pressure of 10,200 psi with PESA at a concentration of 0.4% bwc.
FIG. 2 is a graph of thickening time in minutes (min) versus concentration of PESA for the cement composition at a temperature of 217° F. and a pressure of 10,200 psi.
FIG. 3 is a graph of temperature (° F.) and consistency (Bc) versus time (hr:min) for the cement composition at a pressure of 10,200 psi with PESA at a concentration of 0.4% bwc. The upper lines (beginning at time zero) indicate temperature and the lower line (beginning at time zero) indicates consistency of the cement composition.
FIG. 4 is a graph of temperature (° F.) and consistency (Bc) versus time (hr:min) for the cement composition at a pressure of 10,200 psi additionally containing sodium chloride (NaCl) at a concentration of 35% by weight of the water and PESA at a concentration of 0.4% bwc. The upper lines (beginning at time zero) indicate temperature and the lower line (beginning at time zero) indicates consistency of the cement composition.



DETAILED DESCRIPTION OF THE INVENTION
As used herein, the words “comprise,” “have,” “include,” and all grammatical variations thereof are each intended to have an open, non-limiting meaning that does not exclude additional elements or steps.
As used herein, the words “consisting essentially of” and all grammatical variations thereof are intended to limit the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s) of the claimed invention.
Oil and gas hydrocarbons are naturally occurring in some subterranean formations. A subterranean formation containing oil or gas is sometimes referred to as a reservoir. A reservoir may be located under land or off shore. Reservoirs are typically located in the range of a few hundred feet (shallow reservoirs) to a few tens of thousands of feet (ultra-deep reservoirs). In order to produce oil or gas, a well is drilled into a subterranean formation.
As used herein, a “well” includes at least one wellbore drilled into a subterranean formation, which may be a reservoir or adjacent to a reservoir. A wellbore can have vertical and horizontal portions, and it can be straight, curved, or branched. As used herein, the term “wellbore” refers to a wellbore itself, including any uncased, open-hole portion of the wellbore. A near-wellbore region is the subterranean material and rock of the subterranean formation surrounding the wellbore. As used herein, a “well” also includes the near-wellbore region. The near-wellbore region is considered to be the region within about 100 feet of the wellbore. As used herein, “into a well” means and includes into any portion of the well, including into the wellbore or into the near-wellbore region via the wellbore.
As used herein, a “fluid” is a substance having a continuous phase and that tends to flow and to conform to the outline of its container when the substance is tested at a temperature of 71° F. and a pressure of one atmosphere. An example of a fluid is a liquid or gas.
As used herein, a “fluid” can have more than one distinct phase. For example, a “fluid” can be or include a slurry, which is a suspension of solid particles in a continuous liquid phase; it can be or include an emulsion, which is a suspension of two or more immiscible liquids where droplets of at least one liquid phase are dispersed in a continuous liquid phase of another; or it can be or include a foam, which is a suspension or dispersion of gas bubbles in a continuous liquid phase.
In order to produce oil or gas, a wellbore is drilled into or near a subterranean formation. The wellbore may be an open hole or cased hole. In an open-hole wellbore, a tubing string is placed into the wellbore. The tubing string allows fluids to be introduced into or flowed from a remote portion of the wellbore. In a cased hole, a casing is placed into the wellbore that can contain a tubing string. In an open hole, the space between the wellbore and the outside of a tubing string is an annulus. In a cased hole, the space between the wellbore and the outside of the casing is an annulus. Also, in a cased hole, there may be an annulus between the tubing string and the inside of the casing.
As used herein, a “cement composition” is a mixture of at least cement and water, and the cement composition can include additives. As used herein, the term “cement” means a dry powder substance that acts as a binder to bind other materials together.
During well completion, it is common to introduce a cement composition into an annulus in the wellbore. For example, in a cased hole, the cement composition is placed and allowed to set in the annulus between the wellbore and the casing in order to stabilize and secure the casing in the wellbore. By cementing the casing in the wellbore, fluids are prevented from flowing into the annulus. Consequently, oil or gas can be produced in a controlled manner by directing the flow of oil or gas through the casing and into the wellhead. Cement compositions also can be used in well-plugging operations or gravel-packing operations.
During cementing operations, it is necessary for the cement composition to remain pumpable during introduction into the well and until the composition is situated in the portion of the well to be cemented. After the cement composition has reached the portion of the well to be cemented, the cement composition ultimately sets. A cement composition that thickens too quickly while being pumped can damage pumping equipment or block tubing or pipes, and a cement composition that sets too slowly can cost time and money while waiting for the composition to set.
As used herein, the “thickening time” is how long it takes for a cement composition to become unpumpable under specified temperature and pressure conditions. The pumpability of a cement composition is related to the consistency of the composition. The consistency of a cement composition is measured in Bearden units of consistency (Bc), a dimensionless unit with no direct conversion factor to the more common units of viscosity. As used herein, a cement composition becomes “unpumpable” when the consistency of the composition reaches 70 Bc.
If any test (e.g., thickening time or shear strength) requires the step of mixing, then the grouting composition is “mixed” according to the following procedure. The water of the cement composition is added to a mixing container and the container is then placed on a mixer base. The motor of the base is then turned on and maintained at 4,000 revolutions per minute (rpm). The cement and any other ingredients are added to the container at a uniform rate in not more than 15 seconds (s). After all the cement and any other ingredients have been added to the water in the container, a cover is then placed on the container, and the cement composition is mixed at 12,000 rpm (+/−500 rpm) for 35 s (+/−1 s). It should be understood that the ingredients of a cement composition are mixed at ambient conditions (about 71° F. and about 1 atmosphere pressure).
It is also to be understood that if any test (e.g., thickening time and shear strength) specifies “at” a specific temperature and possibly a specific pressure, then the temperature and pressure of the cement composition is ramped up to the specified temperature and pressure after being mixed at ambient temperature and pressure. For example, the cement composition can be mixed at 71° F. and then placed into the testing apparatus and the temperature of the cement composition can be ramped up to the specified temperature. As used herein, the rate of ramping up the temperature is in the range of about 3° F./min to about 5° F./min. After the cement composition is ramped up to the specified temperature and possibly pressure, the cement composition is maintained at the specified temperature and pressure for the duration of the testing. These increases are achieved at practical rates. Pressurizing can be practically accomplished much more quickly than heating; thus, the cement composition is pressurized much more quickly than it is heated.
As used herein, the consistency of a cement composition is measured as follows. The cement composition is mixed. The cement composition is then placed in the test cell of a High-Temperature, High-Pressure (HTHP) consistometer, such as a Fann Model 275 or a Chandler Model 8240. The cement composition is tested in the HTHP consistometer at the specified temperature and specified pressure. Consistency measurements are taken continuously until the cement composition exceeds 70 Bc.
A cement composition can develop compressive strength. Cement composition compressive strengths can vary from 0 psi to over 10,000 psi. As used herein, compressive strength is measured at a specified time after the composition has been mixed at the specified temperature and pressure. For example, compressive strength can be measured at a time in the range of about 24 to about 48 hours after the composition is mixed at a temperature of 217° F. Compressive strength can be measured by either a destructive method or non-destructive method.
The destructive method mechanically tests the compressive strength of a cement composition sample at a specified time after mixing using a compression-testing machine. The sample is subjected to increasing pressure until it crushes. According to the destructive method, the compressive strength is calculated from the failure load divided by the smallest cross-sectional area in contact with the load-bearing plates of the compression-testing machine resisting the load. The compressive strength is reported in units of pressure, such as pound-force per square inch (psi) or megapascals (MPa).
The non-destructive method continually measures a correlated compressive strength of a cement composition sample throughout the test period by utilizing a non-destructive sonic device such as an Ultrasonic Cement Analyzer (UCA) available from Fann Instruments in Houston, Tex. As used herein, the “compressive strength” of a cement composition is measured utilizing an Ultrasonic Cement Analyzer as follows. The cement composition is mixed. The cement composition is placed in an Ultrasonic Cement Analyzer at the specified temperature and pressure. The UCA continually measures the transit time of the acoustic signal through the sample. The UCA contains preset algorithms that correlate transit time to compressive strength. The UCA reports the compressive strength of the cement composition in units of pressure, such as psi or MPa.
The compressive strength of a cement composition can be used to indicate when the cement composition has initially set and when it has set.
As used herein, a cement composition is considered “initially set” when the cement composition has developed a compressive strength of 50 psi using the non-destructive compressive strength method at a temperature of 217° F. and a pressure of 3,000 psi. As used herein, the “initial setting time” is the difference in time between when the cement is added to the water and when the composition is initially set.
As used herein, a cement composition is considered to be “set” when the cement composition becomes hard or solid. A cement composition becomes set through the process of curing. It may take up to 24 hours or longer for a cement composition to set. Some cement compositions can continue to develop a compressive strength over the course of several days. Some cement compositions can develop a compressive strength of over 10,000 psi.
A set retarder can be added to a cement composition to help increase the thickening time of the cement composition such that the cement composition remains pumpable for a desired time. The thickening time is proportional to the setting time, i.e., the longer the thickening time, the longer the setting time will be. Therefore, a set retarder can be added to a cement composition to help increase the setting time of the cement composition. However, if a set retarder is in too high a concentration, the cement composition may never set. Therefore, the set retarder also can be used in a concentration such that the cement composition sets in a desired time.
Conventional polymeric set retarders have been used to delay the setting time of cement compositions. Examples of conventional set retarders are disclosed in U.S. Pat. No. 7,004,256 issued Feb. 28, 2006 to Chatterji et al., which is incorporated by reference in its entirety. Another example of a conventional set retarder is a copolymer formed from a monomer of 2-acrylamido-2-methylpropane sulfonic acid (“AMPS”). One example of a conventional AMPS set retarder is “SCR-100TM”, available from Halliburton Energy Services, Inc. in Duncan, Okla.
A polymer is a large molecule composed of repeating units typically connected by covalent chemical bonds. The number of repeating units of a polymer can range from approximately 4 to greater than 10,000. The number of repeating units of a polymer is referred to as the chain length of the polymer. A polymer is formed from the polymerization reaction of monomers. A polymer formed from one type of monomer is called a homopolymer. A copolymer is formed from two or more different type monomers. In the polymerization reaction, the monomers are transformed into the repeating units of a polymer. The conditions of the polymerization reaction can be adjusted to help control the average number of repeating units (the average chain length) of a polymer. A polymer also has an average molecular weight, which is directly related to the average chain length of the polymer. The average molecular weight of a polymer has an impact on some of the physical characteristics of a polymer, for example, its solubility in water and its biodegradability.
For a copolymer, each of the monomers will be repeated a certain number of times (number of repeating units). The average molecular weight for a copolymer can be expressed as follows:

Avg. molecular weight=(M.W.m1*RUm1)+(M.W.m2*RUm2) . . .

where M.W.m1 is the molecular weight of the first monomer; RU m1 is the number of repeating units of the first monomer; M.W.m2 is the molecular weight of the second monomer; and RU m2 is the number of repeating units of the second monomer. Of course, a terpolymer would include three monomers, a tetra polymer would include four monomers, and so on.

It should also be understood that, as used herein, “first,” “second,” and “third,” are assigned arbitrarily and are merely intended to differentiate between two or more monomers, fluids, etc., as the case may be, and does not indicate any sequence. Furthermore, it is to be understood that the mere use of the term “first” does not require that there be any “second,” and the mere use of the word “second” does not require that there be any “third,” etc.
In a copolymer, the repeating units for each of the monomers can be arranged in various ways along the polymer chain. For example, the repeating units can be random, alternating, periodic, or block.
For a copolymer made from two monomers, the mole ratio is the ratio of the moles of the first monomer to the moles of the second monomer. For example, a copolymer can have a mole ratio of 50:50, which means that, for every one mole of the first monomer, there is one mole of the second monomer. By way of another example, a mole ratio of 80:20 means that, for every 4 moles of the first monomer, there is one mole of the second monomer. However, for a random copolymer, the mole ratio of the monomers is not as important as it would be for a block copolymer.
Some conventional polymeric set retarders do not increase the thickening time to at least 2 hours in high-temperature wells. As used herein, a high-temperature well is a well with a bottomhole temperature in the range of 150° F. to 500° F. As used herein, the bottomhole temperature refers to the downhole temperature at the portion of the well to be cemented. In order to make some conventional polymeric set retarders increase the thickening time to at least 2 hours in high-temperature wells, the molecular weight of the polymer can be increased (usually to a molecular weight of greater than 10,000).
Some nations have implemented new environmental regulations which set standards for the biodegradability of wellbore fluids (especially for off-shore drilling). Biodegradability is the process by which complex molecules are broken down by microorganisms to produce simpler compounds. However, as the molecular weight of a polymer increases, its biodegradability tends to decrease. Thus, in most of the cases, high molecular weight polymers may not satisfy the new environmental regulations, and, thus, the polymers may not be able to be used. As used herein, a high molecular weight polymer is a polymer that has an average molecular weight of greater than 10,000. As used herein, a low molecular weight polymer is a polymer that has an average molecular weight of less than 10,000.
Also, in general, as the molecular weight of a polymer increases, its solubility decreases. As a result, some high molecular weight polymers are generally water-swellable; whereas, some low molecular weight polymers are generally water soluble. As used herein, a polymer is “water soluble” if at least 1 part by weight of the polymer dissolves in 5 parts by weight of deionized water at a temperature of 80° F.
As used herein, a polymer is considered “biodegradable” if the polymer passes a ready biodegradability test or an inherent biodegradability test. It is preferred that a polymer is first tested for ready biodegradability, and only if the polymer does not pass at least one of the ready biodegradability tests then the polymer is tested for inherent biodegradability. It is believed that the polymer according to the invention will pass the ready biodegradability test and will not need to be tested for inherent biodegradability.
In accordance with Organisation for Economic Co-operation and Development (OECD) guidelines, the following six tests permit the screening of chemicals for ready biodegradability. As used herein, a polymer showing more than 60% biodegradability in 28 days according to any one of the six ready biodegradability tests is considered a pass level for classifying it as “readily biodegradable,” and it may be assumed that the polymer will undergo rapid and ultimate degradation in the environment. The six ready biodegradability tests are: (1) 301 A: DOC Die-Away; (2) 301 B: CO2 Evolution (Modified Sturm Test); (3) 301 C: MITI (I) (Ministry of International Trade and Industry, Japan); (4) 301 D: Closed Bottle; (5) 301 E: Modified OECD Screening; and (6) 301 F: Manometric Respirometry. The six ready biodegradability tests are described below:
(1) For the 301A test, a measured volume of inoculated mineral medium, containing 10 mg to 40 mg dissolved organic carbon per liter (DOC/l) from the polymer as the nominal sole source of organic carbon, is aerated in the dark or diffuse light at 22±2° C. Degradation is followed by DOC analysis at frequent intervals over a 28-day period. The degree of biodegradation is calculated by expressing the concentration of DOC removed (corrected for that in the blank inoculum control) as a percentage of the concentration initially present. Primary biodegradation may also be calculated from supplemental chemical analysis for parent compound made at the beginning and end of incubation.
(2) For the 301B test, a measured volume of inoculated mineral medium, containing 10 mg to 20 mg DOC or total organic carbon per liter from the polymer as the nominal sole source of organic carbon is aerated by the passage of carbon dioxide-free air at a controlled rate in the dark or in diffuse light. Degradation is followed over 28 days by determining the carbon dioxide produced. The CO2 is trapped in barium or sodium hydroxide and is measured by titration of the residual hydroxide or as inorganic carbon. The amount of carbon dioxide produced from the test substance (corrected for that derived from the blank inoculum) is expressed as a percentage of ThCO2. The degree of biodegradation may also be calculated from supplemental DOC analysis made at the beginning and end of incubation.
(3) For the 301C test, the oxygen uptake by a stirred solution, or suspension, of the polymer in a mineral medium, inoculated with specially grown, unadapted micro-organisms, is measured automatically over a period of 28 days in a darkened, enclosed respirometer at 25+/−1° C. Evolved carbon dioxide is absorbed by soda lime. Biodegradation is expressed as the percentage oxygen uptake (corrected for blank uptake) of the theoretical uptake (ThOD). The percentage primary biodegradation is also calculated from supplemental specific chemical analysis made at the beginning and end of incubation, and optionally ultimate biodegradation by DOC analysis.
(4) For the 301D test, a solution of the polymer in mineral medium, usually at 2-5 milligrams per liter (mg/l), is inoculated with a relatively small number of micro-organisms from a mixed population and kept in completely full, closed bottles in the dark at constant temperature. Degradation is followed by analysis of dissolved oxygen over a 28 day period. The amount of oxygen taken up by the microbial population during biodegradation of the test substance, corrected for uptake by the blank inoculum run in parallel, is expressed as a percentage of ThOD or, less satisfactorily COD.
(5) For the 301E test, a measured volume of mineral medium containing 10 to 40 mg DOC/1 of the polymer as the nominal sole source of organic carbon is inoculated with 0.5 ml effluent per liter of medium. The mixture is aerated in the dark or diffused light at 22+2° C. Degradation is followed by DOC analysis at frequent intervals over a 28 day period. The degree of biodegradation is calculated by expressing the concentration of DOC removed (corrected for that in the blank inoculums control) as a percentage of the concentration initially present. Primary biodegradation may also be calculated from supplemental chemical analysis for the parent compound made at the beginning and end of incubation.
(6) For the 301F test, a measured volume of inoculated mineral medium, containing 100 mg of the polymer per liter giving at least 50 to 100 mg ThOD/l as the nominal sole source of organic carbon, is stirred in a closed flask at a constant temperature (+1° C. or closer) for up to 28 days. The consumption of oxygen is determined either by measuring the quantity of oxygen (produced electrolytically) required to maintain constant gas volume in the respirometer flask or from the change in volume or pressure (or a combination of the two) in the apparatus. Evolved carbon dioxide is absorbed in a solution of potassium hydroxide or another suitable absorbent. The amount of oxygen taken up by the microbial population during biodegradation of the test substance (corrected for uptake by blank inoculum, run in parallel) is expressed as a percentage of ThOD or, less satisfactorily, COD. Optionally, primary biodegradation may also be calculated from supplemental specific chemical analysis made at the beginning and end of incubation, and ultimate biodegradation by DOC analysis.
In accordance with OECD guidelines, the following three tests permit the testing of chemicals for inherent biodegradability. As used herein, a polymer with a biodegradation or biodegradation rate of >20% is regarded as “inherently primary biodegradable.” A polymer with a biodegradation or biodegradation rate of >70% is regarded as “inherently ultimate biodegradable.” As used herein, a polymer passes the inherent biodegradability test if the polymer is either regarded as inherently primary biodegradable or inherently ultimate biodegradable when tested according to any one of three inherent biodegradability tests. The three tests are: (1) 302 A-1981 Modified SCAS Test; (2) 302 B-1992 Zahn-Wellens Test; and (3) 302 C-1981 Modified MITI Test. Inherent biodegradability refers to tests which allow prolonged exposure of the test compound to microorganisms, a more favorable test compound to biomass ratio, and chemical or other conditions which favor biodegradation. The three inherent biodegradability tests are described below:
(1) For the 302A test, activated sludge from a sewage treatment plant is placed in an aeration (SCAS) unit. The polymer and settled domestic sewage are added, and the mixture is aerated for 23 hours. The aeration is then stopped, the sludge allowed to settle and the supernatant liquor is removed. The sludge remaining in the aeration chamber is then mixed with a further aliquot of the polymer and sewage and the cycle is repeated. Biodegradation is established by determination of the dissolved organic carbon content of the supernatant liquor. This value is compared with that found for the liquor obtained from a control tube dosed with settled sewage only.
(2) For the 302B test, a mixture containing the polymer, mineral nutrients, and a relatively large amount of activated sludge in aqueous medium is agitated and aerated at 20° C. to 25° C. in the dark or in diffuse light for up to 28 days. A blank control, containing activated sludge and mineral nutrients but no polymer, is run in parallel. The biodegradation process is monitored by determination of DOC (or COD(2)) in filtered samples taken at daily or other time intervals. The ratio of eliminated DOC (or COD), corrected for the blank, after each time interval, to the initial DOC value is expressed as the percentage biodegradation at the sampling time. The percentage biodegradation is plotted against time to give the biodegradation curve.
(3) For the 302C test, an automated closed-system oxygen consumption measuring apparatus (BOD-meter) is used. The polymer to be tested is inoculated in the testing vessels with micro-organisms. During the test period, the biochemical oxygen demand is measured continuously by means of a BOD-meter. Biodegradability is calculated on the basis of BOD and supplemental chemical analysis, such as measurement of the dissolved organic carbon concentration, concentration of residual chemicals, etc.
It has been discovered that a water-soluble, biodegradable homopolymer of epoxysuccinic acid can be used as a set retarder. Another advantage according to the invention is that a water-soluble, biodegradable homopolymer of epoxysuccinic acid is a green scale inhibitor and is biocompatible. As used herein, “biocompatible” means the quality of not having toxic or injurious effects on biological systems. For example, if a cement composition including a homopolymer of epoxysuccinic acid were used in off-shore drilling, then a release of the polymer into the water would not be harmful to aquatic life. Yet another advantage to the polymer is it is salt tolerant. As used herein, “salt tolerant” means that a cement composition containing 325 g of deionized water, 860 g of Class-H Portland Cement, 0.4% bwc of the polymer, and sodium chloride (NaCl) at a concentration of 30% by weight of the water (bww), at a temperature of 125° F. and a pressure of 5,160 psi, will have a thickening time of at least 2 hours. Thus, it is believed that a polymer comprising a monomer or monomers selected from the group consisting of epoxysuccinic acid, a substituted epoxysuccinic acid, and an alkali metal salt, alkaline earth metal salt, or ammonium salt of any of the foregoing, and any combination of any of the foregoing can be water soluble and biodegradable, and, in addition, can be a green scale inhibitor and biocompatible, can be used in the presence of salt, and can be more cost effective compared to conventional set retarders.
According to an embodiment, a cement composition for use in a subterranean formation is provided. The cement composition comprises: (A) cement; (B) water; and (C) a polymer, wherein the polymer: (i) comprises a monomer or monomers selected from the group consisting of epoxysuccinic acid, a substituted epoxysuccinic acid, and an alkali metal salt, alkaline earth metal salt, or ammonium salt of any of the foregoing, and any combination of any of the foregoing; (ii) has the following characteristics: (a) is water soluble; and (b) is biodegradable; and (iii) is capable of providing: (a) a thickening time of at least 2 hours for a test composition at a temperature of 190° F. and a pressure of 5,160 psi; and (b) an initial setting time of less than 24 hours for the test composition at a temperature of 217° F. and a pressure of 3,000 psi, wherein the test composition consists of 860 grams of Class-H Portland cement, 325 grams of deionized water, and 0.4% by weight of the cement of the polymer.
According to another embodiment, a method for cementing in a subterranean formation is provided. The method comprises the steps of: (A) introducing the cement composition into the subterranean formation; and (B) allowing the cement composition to set after introduction into the subterranean formation.
The cement composition includes cement. The cement can be a Portland cement, a pozzalonic cement, a gypsum cement, a high alumina content cement, a silica cement, and any combination thereof. Preferably, the cement is Portland Cement Type I, II, or III. Preferably, the cement is Class A cement, Class C cement, Class G cement, or Class H cement. Preferably, the cement composition has a density in the range of about 9 to about 22 pounds per gallon (ppg).
The cement composition includes water. The water can be selected from the group consisting of freshwater, brackish water, and saltwater, in any combination thereof in any proportion. The cement composition also can include salt. Preferably, the salt is selected from sodium chloride, calcium chloride, calcium bromide, potassium chloride, potassium bromide, magnesium chloride, and any combination thereof in any proportion. Preferably, the salt is in a concentration in the range of about 0.1% to about 40% by weight of the water.
The cement composition includes a polymer, wherein the polymer comprises a monomer or monomers selected from the group consisting of epoxysuccinic acid, a substituted epoxysuccinic acid, and an alkali metal salt, alkaline earth metal salt, or ammonium salt of any of the foregoing, and any combination of any of the foregoing in any proportion. Preferably, any of the other monomers that may be present in the polymer are not AMPS or lignosulfonate and its salts.
Preferably, the polymer consists essentially of a monomer or monomers selected from the group consisting of epoxysuccinic acid, a substituted epoxysuccinic acid, and an alkali metal salt, alkaline earth metal salt, or ammonium salt of any of the foregoing, and any combination of any of the foregoing. The polymer can contain other monomers so long as the presence of the other monomers does not materially affect the basic and novel characteristics of the claimed invention.
The polymer can be an alkali metal salt, an alkaline earth metal salt, or an ammonium salt. The monomer(s) can be neutralized prior to the polymerization reaction. The polymer can be neutralized or at least partially neutralized after the polymerization reaction. An example of such an alkali metal salt is sodium polyepoxysuccinate. An example of such an alkaline earth metal salt is calcium polyepoxysuccinate. An example of such an ammonium salt is ammonium polyepoxysuccinate.
The polymer can be a homopolymer having the following structural formula:




where M=hydrogen (H+), sodium (Na+), potassium (K+), or ammonium (NH4+) and where R=hydrogen or a hydrocarbyl of 1 to 4 carbons (C1-4). M1 and M2 can be the same or different, for example, M1 can be H+ and M2 can be K. Also, R1 and R2 can be the same or different. Preferably the hydrocarbyl is an aliphatic group such as methyl, ethyl, propyl, butyl, isopropyl, etc. Preferably, the polymer has an average chain length (n) in the range of 3 to 60. More preferably, the polymer has an average chain length (n) of 3 to 30.

The polymer can be, for example, a homopolymer of epoxysuccinic acid (ESA) or a homopolymer of a substituted ESA. Referring to the structural formula above, a homopolymer of ESA is where both M1 and M2=H+ and both R1 and R2=H. A homopolymer of a substituted ESA is where both M1 and M2=H+ and where at least one of the R1 and R2=a hydrocarbyl of 1 to 4 carbons.
The polymer can be a homopolymer formed from monomers selected from an alkali metal salt of ESA, an alkaline earth metal salt of ESA, and an ammonium salt of ESA, in which both R1 and R2=H. By way of example, a homopolymer formed from an ammonium salt of ESA is where at least one of M1 and M2=NH4+. As mentioned elsewhere herein, it should be understood that a homopolymer of ESA can be at least partially neutralized after the polymerization, for example neutralized with ammonia to form an at least partially neutralized ammonium salt of polyepoxysuccinic acid.
The polymer can be a homopolymer formed from monomers selected from an alkali metal salt of a substituted ESA, an alkaline earth metal salt of a substituted ESA, and an ammonium salt of a substituted ESA, in which at least one of R1 and R2 is a hydrocarbyl of 1 to 4 carbons. By way of example, a homopolymer formed from an ammonium salt of a substituted ESA is where at least one of M1 and M2=NH4+ and at least one of R1 and R2=C1-4.
Most preferably, the homopolymer is polyepoxysuccinic acid.
The polymer can be a copolymer formed from two or more different monomers selected from ESA, a substituted ESA, and an alkali metal salt, alkaline earth metal salt, and an ammonium salt of any of the foregoing. By way of example, the polymer can be a copolymer formed from two or more different monomers selected from substituted ESAs. For example, the first substituted ESA monomer can have R1=C1; whereas, the second substituted ESA monomer can have R1=C3. Preferably, if the polymer is a copolymer, then the repeating units are random.
Among other things, the polymer has an average molecular weight such that the polymer has the following characteristics: it is water soluble; it is biodegradable; and it provides the desired thickening time and initial setting time to the cement composition. Preferably, the polymer has an average molecular weight in the range of about 400 to about 8,000. More preferably, the polymer has an average molecular weight in the range of about 400 to about 4,000. Most preferably, the polymer has an average molecular weight in the range of about 400 to about 1,500.
Preferably, the polymer is in at least a sufficient concentration such that the cement composition has a thickening time of at least 3 hours at a temperature of 217° F. and a pressure of 10,200 psi, whereas an otherwise identical cement composition without the polymer would have a thickening time of less than 3 hours at the same temperature and pressure. Preferably, the polymer is in a concentration equal to or less than a sufficient concentration such that the cement composition sets in less than 48 hours at a temperature of 217° F. and a pressure of 3,000 psi. Preferably, the polymer is in a concentration in the range of about 0.01% to about 10% by weight of the cement (bwc). More preferably, the polymer is in a concentration in the range of about 0.02% to about 2% bwc. One of skill in the art will be able to determine the concentration of the polymer needed in order to achieve the desired thickening time, for example, based on the amount of salt which may be present in the water and the bottomhole temperature of the well, among other specific conditions of the well.
Preferably, the cement composition has a thickening time in the range of about 3 to about 10 hours at a temperature of 217° F. and a pressure of 10,200 psi. More preferably, the cement composition has a thickening time in the range of about 4 to about 7 hours at a temperature of 217° F. and a pressure of 10,200 psi. Some of the variables that can affect the thickening time of the cement composition include the concentration of the polymer, the concentration of any salt present in the cement composition, and the bottomhole temperature of the well. Preferably, the cement composition sets in less than 48 hours at a temperature of 217° F. and a pressure of 3,000 psi. More preferably, the cement composition sets in less than 24 hours at a temperature of 217° F. and a pressure of 3,000 psi. Most preferably, the cement composition sets at a time in the range of about 8 to about 24 hours at a temperature of 217° F. and a pressure of 3,000 psi.
Preferably, the cement composition has a compressive strength of at least 500 psi when tested at 24 hours at a temperature of 217° F. and a pressure of 3,000 psi. More preferably, the cement composition has a compressive strength in the range of about 500 to about 10,000 psi when tested at 24 hours at a temperature of 217° F. and a pressure of 3,000 psi.
The cement composition can also include at least one additional set retarder to help control the thickening time of the cement composition. Preferably, any additional set retarder is also biodegradable.
The cement composition can include at least one additive suitable for use in subterranean cementing operations. Examples of such additives include, but are not limited to, a strength-retrogression additive, a set accelerator, a set retarder, a weighting agent, a lightweight additive, a gas-generating additive, a mechanical property enhancing additive, a lost-circulation material, a filtration-control additive, a dispersant, a fluid loss control additive, a defoaming agent, a foaming agent, a thixotropic additive, a nano-particle, and combinations thereof. Preferably, any other additives are also biodegradable. For example, the cement composition can include a strength-retrogression additive. The strength-retrogression additive can be selected from the group consisting of course silica flour, fine silica flour, and any combination thereof in any proportion. Preferably, the strength stabilizer is in a concentration in the range of about 20% to about 50% by weight of the cement.
The cement composition can include a fluid loss additive. Suitable examples of fluid loss additives include HALAD®344, HALAD®413, HALAD®400, HALAD®9, HALAD®14, HALAD®23, HALAD®100A, HALAD®300, HALAD®350, HALAD®400L, HALAD®600, HALAD®600LE+, HALAD®613, HALAD®766, FDP-703, Latex 2000, LAP-1, and LA-2, available from Halliburton Energy Services, Inc. Preferably, the fluid loss additive is in a concentration in the range of 0.1% to 4% by weight of the cement. The fluid loss additive is preferably biodegradable. Examples of suitable biodegradable fluid loss additives include HALAD®400 and HALAD®300.
The cement composition can include a dispersant. Suitable examples of dispersants include CFR®2, CFR®3, CFR®5LE, CFR®6, CFR®8, FDP-701, and FDP-C-850, available from Halliburton Energy Services, Inc. Preferably, the dispersant is in a concentration in the range of 0.05% to 3% by weight of the cement.
The cement composition also can include a filler material. Suitable examples of filler materials include, but are not limited to, fly ash, sand, clays, and vitrified shale. Preferably, the filler material is in a concentration in the range of about 5% to about 50% by weight of the cement.
The cement composition also can include other additives. Commercially-available examples of other additives include, but are not limited to, SSA-1, SSA-2, High Dense-3, High Dense-4, Barite, Micromax, Silicalite, HGS-6000, HGS-4000, HGS-10000, Well life 665, Well life 809, and Well life 810, available from Halliburton Energy Services, Inc.
The method includes the step of introducing the cement composition into a subterranean formation. Preferably, the subterranean formation is penetrated by a well and the step of introducing is into a portion of the well. Preferably, the portion of the well is a portion of an annulus. The step of introducing can be for the purpose of well completion, primary or remedial cementing operations, squeeze cementing, well-plugging, or gravel packing. The cement composition is in a pumpable state upon introduction into the subterranean formation. The method also includes the step of allowing the cement composition to set after introduction into the subterranean formation. The method can include the additional steps of perforating, fracturing, or performing an acidizing treatment, after the step of allowing the cement composition to set.
If the step of introducing is into a portion of a well, then preferably, the cement composition has a thickening time of at least 3 hours at the bottomhole temperature and pressure of the well. More preferably, the cement composition has a thickening time in the range of about 4 to about 10 hours at the bottomhole temperature and pressure of the well. For example, one of skill in the art will be able to select the thickening time based on the specific conditions of the well (e.g., the length of the casing and the bottomhole temperature of the well). Some of the variables that can affect the thickening time of the cement composition include the concentration of the polymer, the concentration of any salt present in the cement composition, and the bottomhole temperature of the well. Preferably, the cement composition sets in less than 48 hours at the bottomhole temperature and pressure of the well. More preferably, the cement composition sets in less than 24 hours at the bottomhole temperature and pressure of the well. Most preferably, the cement composition sets at a time in the range of about 8 to about 24 hours at the bottomhole temperature and pressure of the well. Preferably, the cement composition is used in a well having a bottomhole temperature of at least 150° F. Preferably, the bottomhole temperature is in the range of about 150° F. to about 500° F. More preferably, the bottomhole temperature is in the range of about 180° F. to about 400° F. Most preferably, the bottomhole temperature is in the range of about 180° F. to about 350° F. Preferably, the cement composition develops a compressive strength of at least 1,500 psi after the cement composition has been introduced into the well and is situated in the portion of well to be cemented.
EXAMPLES
To facilitate a better understanding of the present invention, the following examples of certain embodiments are given. The following examples are not the only examples that could be given according to the present invention and are not intended to limit the scope of the invention.
Table 1 and FIGS. 1, 2, and 3 show the effect of the concentration of a polymer or temperature of the cement composition on thickening time. For Table 1 and FIGS. 1, 2, and 3 several cement compositions, having a density of 16.4 pounds per gallon (ppg), were prepared. The cement compositions consisted of 5.48 gallons of deionized water; Class-H cement; SSA-2TM strength stabilizer at a concentration of 35% by weight of the cement (bwc); HALAD®344 fluid loss additive at a concentration of 0.5% bwc; and a set retarder. Table 1 shows the thickening time for the cement compositions at a pressure of 10,200 psi, wherein the set retarder is either SCR-100TM (a conventional polymeric set retarder) or polyepoxysuccinic acid (“PESA”) having an average molecular weight in the range of 400-1,500. FIG. 1 is a graph of thickening time versus temperature for the cement composition at a pressure of 10,200 psi with PESA at a concentration of 0.4% bwc. FIG. 2 is a graph of thickening time versus concentration of PESA for the cement composition at a temperature of 217° F. and a pressure of 10,200 psi. FIG. 3 is a graph of temperature (° F.) and consistency (Bc) versus time (hr:min) for the cement composition at a pressure of 10,200 psi with PESA at a concentration of 0.4% bwc. For Table 1, the cement compositions were heated from an initial temperature of 70° F. to a maximum temperature of at least 140° F. over the course of 44 minutes and then maintained at that maximum temperature. The thickening time is the time it took for the cement compositions to reach 70 Bc. The consistency of the cement compositions was measured using a Fann Model 275 HTHP consistometer. The initial setting time of the cement compositions was the time it took for the cement compositions to reach 50 psi, at a pressure of 3,000 psi, using an Ultrasonic Cement Analyzer.













TABLE 1








Concen-






Cement
tration
Temper-
Thickening
Initial Setting



Set
of Retarder
ature
Time
Time



Retarder
(% bwc)
(° F.)
(hr:min)
(hr:min)





















1
SCR-100
0.4
217
4-6
11:24


2
PESA
0.05
140
4:09
Not measured


3
PESA
0.1
190
4:34
Not measured


4
PESA
0.4
190
19:50 
Not measured


5
PESA
0.2
217
3:40
09:33


6
PESA
0.4
217
8:06
14:34


7
PESA
0.6
217
9:33
Not measured


8
PESA
0.4
245
3:17
Not measured


9
PESA
0.8
280
2:15
Not measured


10
PESA
1.5
280
6:02
Not measured









As can be seen in Table 1 and FIG. 1, for a fixed concentration of PESA, the thickening time decreases with an increase in temperature. As can also be seen in Table 1, PESA performs comparably to the conventional polymeric set retarder SCR-100TM. As can be seen in Table 1 and FIG. 2, for a fixed temperature, the thickening time increases with an increase in concentration of PESA. As can be seen in FIG. 3, it took approximately 3 hours for the cement composition to reach approximately 100 Bc at a temperature of approximately 245° F.
Table 2 and FIG. 4 show the effect of salt in the cement composition on thickening time. For Table 2 several 16.4 ppg cement compositions were prepared containing 5.48 gallons of deionized water, seawater, or saltwater having varying concentrations of salt; Class-H cement; SSA-2TM strength stabilizer at a concentration of 35% bwc; HALAD®344 fluid loss additive at a concentration of 0.5% bwc; and PESA at a concentration of 0.4% bwc. For Table 2, the cement compositions were heated from an initial temperature of 70° F. to a maximum temperature of 217° F. over the course of 44 minutes and then maintained at 217° F. and a pressure of 10,200 psi. The thickening time is the time it took for the cement compositions to reach 70 Bc. The consistency of the cement compositions was measured using a Fann Model 275 HTHP consistometer. For FIG. 4, a 16.4 ppg cement composition was prepared containing 5.48 gallons of water; sodium chloride (NaCl) at a concentration of 35% by weight of the water (bww); Class-H cement; SSA-2TM strength stabilizer at a concentration of 35% bwc; HALAD®344 fluid loss additive at a concentration of 0.5% bwc; and PESA at a concentration of 0.4% bwc. FIG. 4 is a graph of temperature (° F.) and consistency (Bc) versus time (hr:min) for the cement composition maintained at 10,200 psi.













TABLE 2








Concentration
Concen-





Cement
of Set
tration
Temper-
Thickening



Set
Retarder
of NaCl
ature
Time



Retarder
(% bwc)
(% bww)
(° F.)
(hr:min)





















1
PESA
0.4
Not Present
217
8:06


2
PESA
0.4
Sea Water
217
6:19


3
PESA
0.4
10
217
6:43


4
PESA
0.4
35
217
16:27 









As can be seen in Table 2, NaCl acts as an accelerator for the cement composition when the concentration of the salt is ≦15% bww. But NaCl shows a retarding effect when the concentration of NaCl is in the range of 20-35% bww. For that reason, the thickening time of slurry 2 and 3 decreases compared to slurry 1 and the thickening time of slurry 4 increases compared to slurry 1. As can be seen in FIG. 4, it took approximately 16 hours for the cement composition to reach approximately 100 Bc at a temperature of approximately 215° F.
Table 3 shows the rheology of various cement compositions. For Table 3 several 16.4 ppg cement compositions were prepared containing 5.48 gallons of deionized water; Class-H cement; SSA-2TM strength stabilizer at a concentration of 35% bwc; HALAD®344 fluid loss additive at a concentration of 0.5% bwc; and varying concentrations of PESA. The rheology of the cement compositions were measured using a FANN 35 viscometer with a standard Bob and Sleeve attachment and Spring number 1 at a temperature of 70° F. and a dial reading of 3 to 600 revolutions per minute (rpm).








TABLE 3







PESA
Revolutions per minute (rpm)















Concentration (% bwc)
3
6
30
60
100
200
300
600


















0.2
3
5
16
29
41
78
109
185


0.4
9
11
21
42
58
96
137
233


0.6
9
11
25
38
53
85
120
208









As can be seen in Table 3, the cement compositions containing PESA exhibit acceptable rheology across a wide concentration range. Little variation in dial reading has been found with an increase in PESA concentration from 0.2% bwc to 0.4% bwc. However, a further increase in the concentration of PESA does not affect the rheologies, which indicate its utility at high concentrations (>0.6% bwc).
Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is, therefore, evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods also can “consist essentially of” or “consist of” the various components and steps. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a to b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an”, as used in the claims, are defined herein to mean one or more than one of the element that it introduces. If there is any conflict in the usages of a word or term in this specification and one or more patent(s) or other documents that may be incorporated herein by reference, the definitions that are consistent with this specification should be adopted.

## Claims

1. A cement composition for use in a subterranean formation, the cement composition comprising:
(A) cement;
(B) water; and
(C) a polymer, wherein the polymer:
(i) comprises a monomer or monomers selected from the group consisting of epoxysuccinic acid, a substituted epoxysuccinic acid, and an alkali metal salt, alkaline earth metal salt, or ammonium salt of the epoxysuccinic acid or substituted epoxysuccinic acid;
(ii) has the following characteristics:
(a) is water soluble; and
(b) is biodegradable; and

(iii) is capable of providing:
(a) a thickening time of at least 2 hours for a test composition at a temperature of 190° F. and a pressure of 5,160 psi; and
(b) an initial setting time of less than 24 hours for the test composition at a temperature of 217° F. and a pressure of 3,000 psi,
wherein the test composition consists of 860 grams of Class-H Portland cement, 325 grams of deionized water, and 0.4% by weight of the cement of the polymer.

2. The cement composition according to claim 1, wherein the polymer consists essentially of a monomer or monomers elected from the group consisting of epoxysuccinic acid, a substituted epoxysuccinic acid, and an alkali metal salt, alkaline earth metal salt, or ammonium salt of the epoxysuccinic acid or substituted epoxysuccinic acid.

3. The cement composition according to claim 1, wherein the cement is selected from the group consisting of a Portland cement, a pozzalonic cement, a gypsum cement, a high alumina content cement, a silica cement, and any combination thereof.

4. The cement composition according to claim 1, wherein the cement is selected from the group consisting of Class A cement, Class C cement, Class G cement, and Class H cement.

5. The cement composition according to claim 1, wherein the polymer is in at least a sufficient concentration such that the cement composition has a thickening time of at least 3 hours at a temperature of 217° F. and a pressure of 10,200 psi, whereas an otherwise identical cement composition without the polymer would have a thickening time of less than 3 hours at the same temperature and pressure.

6. The cement composition according to claim 1, wherein the polymer is in a concentration equal to or less than a sufficient concentration such that the cement composition sets in less than 48 hours at a temperature of 217° F. and a pressure of 3,000 psi.

7. The cement composition according to claim 1, wherein the polymer is in a concentration in the range of about 0.01% to about 10% by weight of the cement.

8. The cement composition according to claim 1, wherein the polymer is in a concentration in the range of about 0.02% to about 2% by weight of the cement.

9. The cement composition according to claim 1, wherein the polymer has an average molecular weight in the range of about 400 to about 8,000.

10. The cement composition according to claim 1, wherein the polymer has an average molecular weight in the range of about 400 to about 5,000.

11. The cement composition according to claim 1, wherein the polymer has an average molecular weight in the range of about 400 to about 1,500.

12. The cement composition according to claim 1, wherein the polymer is a homopolymer and the monomer is a substituted epoxysuccinic acid.

13. The cement composition according to claim 1, wherein the polymer is a homopolymer and the monomer is epoxysuccinic acid.

14. The cement composition according to claim 1, wherein the cement composition has a thickening time of at least 3 hours at a temperature of 217° F. and a pressure of 10,200 psi.

15. The cement composition according to claim 1, wherein the cement composition has a thickening time in the range of about 4 to about 10 hours at a temperature of 217° F. and a pressure of 10,200 psi.

16. The cement composition according to claim 1, wherein the cement composition has a compressive strength of at least 500 psi when tested at 24 hours at a temperature of 217° F. and a pressure of 3,000 psi.

17. The cement composition according to claim 1, wherein the cement composition has a compressive strength in the range of 500 to 10,000 psi when tested at 24 hours at a temperature of 217° F. and a pressure of 3,000 psi.