CA2049518A1

CA2049518A1 - Method of reducing fluid loss in cement compositions

Info

Publication number: CA2049518A1
Application number: CA 2049518
Authority: CA
Inventors: Jerry D. Childs; John Burkhalter
Original assignee: Individual
Current assignee: Halliburton Co
Priority date: 1990-08-21
Filing date: 1991-08-20
Publication date: 1992-02-22
Also published as: GB2247234B; GB2247234A; GB9118067D0

Abstract

ABSTRACT
Cementing compositions having improved fluid loss capa-bilities, improved corrosion resistance, improved settling characteristics for use in elevated temperature environments in subterranean formation cementing operations are disclosed. More particularly, such compositions include water, hydraulic cement, a styrene/butadiene latex, the styrene to butadiene being present in a ratio of 10/90 to 90/10 by weight and a surfactant comprising a salt of a C12-15 Pareth 10-40 sulfonate. For use at temperatures above 200°F. a stabilizer and retarder comprising a selected copolymer of AMPS?/acrylic acid also preferably is present (AMPS? is a trademark of The Lubrizol Corporation for 2-acrylamido-2-methylpropanesulfonic acid). Additionally, methods of cementing a conduit in a borehole penetrating an earthen formation by introducing such a cementing com-position into the space between such a conduit and a formation are disclosed.

Description

"MæTHOD OF RED~CIN~ FLUID LOSS
IN CEMENT COMPOSITIO~S"
Background Of The Invention 1. Field Of The Invention .
The present invention relates to an aqueous cementing composition and method of using the same in cementing wellbores penetrating a subterranean formation. More par-ticularly, the present invention concerns the incorporation of styrene-butadiene latexes and a selected surfactant com-position in a cementing composition to minimize fluid loss to a subterranean formation whereby gas migration from the formation into the cement can be minimized.

2. De~criPtion Of The Prior Art In the production of hydrocarbons from a subterranean formation, the subterranean formations are typically cemented or sealed by pumping an aqueous hydraulic cement slurry into the annulus between the pipe and the formation.
In the oft practiced placement of cement in the annular space between the casing of an oilwell and the surrounding subterranean formation, the cement slurry is commonly pumped into the casing and back up the annular space o~tside the casing. Occasionally, the cement is introduced directly to the annular space at the outer side of the casing. Where the cement has been pumped down the casing initially, any cement slurry which remains in the casing is displaced into the annulus by a suitable fluid or fluids.
On some occasions, the zones adjacent the cement con-taining annulus contain connate gas under substantial pressure. In these instances, an undesirable phenomenon referred to in the art as gas leakage is sometimes encoun-tered in which the formation gas enters the annular space which surrounds the well casing after the primary cementing slurry has been placed. This gas can migrate to the sur-face, or other subterranean zones, through the annulus and the cement, forming a permanent flow channel or a highly permeable cement and the leakage is detrimental to the long term integrity and sealing efficiency of the cement in the annulus and the magnitude of such leakage is often enough to require an expensive remedial squeeze cementing job to be carried out to suppress or stop the gas leakage. Such gas leakage can cause high volume blow-outs shortly after the cement placement and before the cement has initially set.
Gas leakage occurs even though the initial hydrostatic pressure throughout the column of the cement slurry placed in the annulus far exceeds the pressure of gas in the for-mation from which the leaking gas originates. In explana-tion, it is theorized that two different wellbore conditions can occur which will allow gas entry into the annulus. The first condition which is believed to be a prerequisite for annular fluid-gas migration is gellation of the cement slurry and subsequent development of static gel strength.
This condition starts shortly after the cement slurry beco-mes static. The pressure required to move the cement is then directly related to the column length and the static gel strength. Thus as static gel strength increases, there is a loss of ability to transmit hydrostatic pressure.

The second condition which contributes directly to the loss of pressure in the cement column (and across the pressurized gas zone) is the loss of fluid and volume reduction within the cement column. This condition is believed to be due to the leak-off of water in the cement into the formations and from cement volume reduction due to the cement hydration.
Volume reductions occurring after static gel strength starts to develop results in a loss of pressure in the cement column. As the pressure in the cement column drops below the gas pressure, gas will enter the annulus. If at this time the static gel strength is still below the gas percolation value, a gas leakage condition i8 created.
Interestingly, the gelled or partially set cement, although it is incapable of maintaining or transmitting full hydrostatic pressure, still is not sufficiently rigid or set to prevent the entry of gas into the annulus and the upward percolation of the gas. According to the most popular theories, an absolute volume reduction occurring after the cement column can no longer transmit full pressure reduces the pore pressure of the still semi-plastic slurry. When the pore pressure alls below the formation gas pressure, formation gas leaks into the wellbore and if the cement is not gelled enough to prevent percolation, gel leakage chan-nels are formed. Two principal mechanisms which act to decrease the pore pressure are the hydration reaction of cement and the loss of filtrate to the adjacent permeable formation.

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Gas leakage problems have been noticed following casing cementing operations on surface conductors and inter-mediate, production and liner jobs. Gas returns to the sur-face have often been noticed within one to seven hours after placement of the cement. Many times, however, the gas flow does not return to the surface, but flows into low pressure zones causing interzonal gas communication.
Another problem experienced when conventional cement slurries are utilized in cementing wellbores in a sub-terranean formation concerns the susceptability of the cement to attack by corrosive fluids. The corrosive fluids may be introduced into the subterranean formation by a treatment performed from the surface, such as injection of acidizing fluids to enhance formation permeability or carbon dioxide to energize or thin hydrocarbon fluids in the for-mation or generated downhole by reaction of various com-pounds such as in various insitu mining processes or the corrosive fluid may be naturally present in the formation such as hydrogen sulfide in some oil-bearing formations.
Yet another problem concerns the behavior of conven-tional cement slurries when exposed to elevated temperatures in the subterranean formation. As the temperature increases, the cement slurry begins to thin and settling of the heavier particles in the slurry can occur. This results in poor or incompetent cement bonds within the subterranean formation. Conventional practice would dictate the use of a material to viscosify the cement slurry to slow the settling process. Unfortunately, addition of viscosifying materials v can make mixing of the cement slurry at ambient conditions of the surface extremely difficult or even impossible.
One partial solution has been the composition disclosed in U.S. Patent 4,537,918 which comprises water, hydraulic cement, a styrene-butadiene copolymer latex (70-30 to 30-70 weight percent ratio) and a latex stabilizer selected from the group of (i) lignosulfonates and their partly desulfo-nated derivatives, (ii) sulfonic acid or sulfite modified melamine-formaldehyde resins, (iii) formaldehyde/sulfonate naphthalene resins and (iv) condensation products of binuclear sulfonated phenols and of formaldehyde. This system is limited in that cnly the particular styrene/butadiene latices will function in the composition.
Too large a quantity of butadiene provokes premature coagu-lation of the latex and too much styrene prevents film for-mation in the slurry. This patent also generally describes the prior uses in which latex latices have been employed in the oil and gas industry. Although latices have been uti-lized in the oil industry, the compositions whic~ have been recommended have been unable to solve the gas migration problem because of difficulties of pumping, flocculation of the latex, uses limited to low temperatures and particular latice ratios.
It would be desirable to provide a composition which is effective from low temperatures of from about 30F. to tem-peratures in excess of 450F. and which would not experience the problems or limitations of the prior art compositions.

SUMMARY OF THE INVENTION
Cementing compositions having improved fluid loss capa-bilities for use in elevated temperature environments in subterranean formation cementing operations are disclosed.
More particularly, such compositions include water, hydraulic cement, a styrene/butadiene latex, the styrene to butadiene being present in a ratio of 10/90 to 90/10 by weight and a surfactant comprising a compound of the general formula R ( OR )n SO3 X
wherein X is any compatible cation, R is selected from the group consisting of Cl - C30 alkyl, Cs - C6 cycloalkyl, Cl -C4 alkyl substituted Cs - C6 cycloalkyl, phenyl, alkyl substituted phenyl of the general formula (R")a Ph- wherein Ph is phenylene and R is Cl - Clg alkyl and a is an integer of from 1 to 3, phen (Cl - Clg) alkyl having a total of from about 8 to 28 carbon atoms, R is a substituted ethylene group - CH2 - CH (R ) wherein R''' is selected from hydro-gen, methyl, ethyl or mixtures thereof and n is a number from O to 40 provided that when R is phenyl or alkyl substi-tuted phenyl, n is at least 1. Preferably, the surfactant comprises a salt of the general formula H(CH2)d (OCH2CH2)e SO3- X+ wherein d is in the range of from about 5-20 and e is in the range of from about 10 to 40 and X is any com-patible cation. For use at temperatures above 200F., a stabilizer and retarder comprising a selected copolymer of AMPSO/acrylic acid also preferably is present (AMPS~ is a trademark of The Lubrizol Corporation for ~ ~J ,: ~J '' ,~ ~ ~

2-acrylamido-2-methylpropanesulfonic acid). Additionally, methods of cementing a conduit in a borehole penetrating an earthen formation by introducing such a cementing com-position into the space between such a conduit and a for-mation are disclosed.
DESCRIPTION OF THE PREFERRED EMBODIMENT
New cementing compositions and methods of using the same in subterranean cementing operations are disclosed. The cementing compositions include water, hydraulic cement, a selected styrene/butadiene latex and a selected surfactant.
The term "cement" or "hydraulic cement" as used herein is intended to include those compounds of calcium, aluminum, silicon, oxygen and/or sulfur which set and harden by reac-tion with water. Such compounds include, for example, Portland cement and particularly Portland cement of API
classe~ G and H, although other classes may be utilized, pozzolan cements, gypsum cements, high alumin'a content cements, silicate cements and high alkalinity cements can be utilized in various applications of the present invention.
Portland cements are preferred.
The water utilized in the cement composition can be water from any source provided that it does not contain an excess of any compounds that effect the stability of the cement composition of the present invention. The water can contain various salts such as sodium, potassium or calcium chloride and the like. Depending upon the particular cement slurry being formed and the intended conditions of use, the water is utilized in the cementing composition in an amount ~,~ F~: ~ c in the range of from about 20 to about 150% by weight of dry cement.
The latex is selected from styrene/butadiene latices and more particularly from styrene(10-90% by weight) / butadiene (90-10% by weight) and particularly those having the ratio of about 20/80 to about 80/20 and most particularly those having a styrene/butadiene ratio of from about 20/80 to about 30/70. It is understood that the styrene/butadiene latice described above generally is commercially produced as a terpolymer latex and the definition of the latex as used herein also is intended to include such terpolymer latices which include from about 0 to 3% by weight of a third monomer to assist in stabilizing the latex emulsion. The third monomer, when present, generally is anionic in character and has a carboxylate, sulfate or sulfonate group.
Other groups that may be present on the third monomer include phosphates, phosphonates or phenolics. Nonionic groups which exhibit steric effects and which contain long ethoxylate or hydrocarbon tails also can be present.
The most preferred ratio has been found to provide excellent fluid loss control to a cement slurry without pre-mature coagulation or loss of compressive strength in the set cement. Latex latices of the type described above are available, for example, from Unocal Chemicals Division of Unocal Corporation, Chicago, Illinois or Reichhold Chemicals, Inc. Dover, Delaware.
The latex is present in the composition in an amount of from about 4 to about 35% by weight of dry cement.

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_g_ Preferably, the latex is present in the composition in an amount of from about 15 to about 25% by weight of dry cement.
The surfactant present in the composition comprises a compound of the general formula R ( OR )n S3 X
wherein X is any compatible cation, R is selected from the group consisting of Cl - C30 alkyl, Cs - C6 cycloalkyl, Cl - C4 alkyl substituted Cs - C6 cycloalkyl, phenyl, alkyl substituted phenyl of the (R")a Ph- wherein Ph is phe-nylene and R is Cl - Clg alkyl and a is an integer of from 1 to 3, phen (Cl - Clg) alkyl having a total of from about 8 to 28 carbon atoms, R is a substituted ethylene group - CH2 - CH (R ) wherein R is selected from hydrogen, methyl, ethyl or mixtures thereof and n is a number from O to 40 provided that when R is phenyl or alkyl substituted phenyl, n is at least 1. Preferably the surfactant comprises a salt of the general formula H(CH2)d(0C2H4)eS03- X+ wherein d is in a range of from about 5-20, e in the range of from about 10 to about 40 and X is a compatible cation. A preferred surfactant is the sodium salt having the chemical formula H(CH2)12-15(C2H4)15S3 Na+ which is commercially available from PPG-Mazer, Gurnee, Illinois. The surfactant is present in the composition in an amount of from about 5 to about 40%
by weight of latex present and preferably is present in an amount of from about 10 to about 25% by weight of latex.
Other types of well known and conventional additives also can be incorporated into the cement slurry composition to modify the properties of the composition. Such additives ~ .3 include additional fluid loss control additives such as, for example, cellulose derivatives such as carboxymethyl-hydroxyethyl cellulose, hydroxyethyl cellulose, modified polysaccharides, polyacrylamides, guar gum derivatives, AMPS~ copolymers, polyethyleneamine and the like.
Dispersing agents can be utilized to facilitate using lower quantities of water and to promote higher set cement strength. Friction reducers which promote freer movement of the unset composition can be incorporated in amounts up to about several percent by weight of dry cement.
Defoaming or antifoaming agents can be utilized in the composition to reduce or substantially eliminate foaming upon formation of the cement slurry. The defoamer can comprise substantially any of the compounds known for such capabilities such as the silicon oil compounds. Such agents generally would be admixed with the cement slurry in an amount of from about 0.02 to about 0.08 gal. per sack of dry cement.
- Accelerators, such as the soluble inorganic salts in addition to calcium chloride, can be utilized in an amount of up to several percent by weight of the dry cement in various situations.
Retarders may be utilized when the bottom hoie cir-culating temperature exceeds 150F. Retarders satisfactory for use in the present invention include those commercially available products commonly utilized as retarders. Examples include lignosulfonates such as calcium lignosulfonate and sodium lignosulfonate; organic acids such as tartaric acid and gluconic acid and the like. The proper amount of retarder required in any particular case should be deter-mined by running a "thickening time" test for the particular retarder and cement composition being utilized. Such tests may be run in accordance with the procedures set forth in API Specification For Materials And Testing For Well Cements, API Spec. 10. Generally, "thickening time" is defined in Spec. 10 as the elapsed time from the time pumping begins until the cement reaches from about 70 to 100 units of consistency. In most applications, the amount of retarder, if any, required will not exceed 6 percent by weight of the dry cement.
A particularly preferred retarder is a copolymer or copolymer salt of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid. The copolymer comprises from about 40 to about 60 mole percent AMPS0 with the balance comprising acrylic acid. The copolymer has an average molecular weight below about 5000. This retarder preferably is utilized in the composition when the bottom hole circulating temperature exceeds about 200F. Surprisingly, this retarder has been found to both retard the setting of the cement at the ele-vated formation temperatures and to stabilize the latex latice against agglomeration or inversion at the elevated temperature. The copolymer can be present in the cement composition in an amount of from about 0.05 to about 3% by weight of dry cement.
Weighting agents such as various oxides of iron, barite, titanium and the like may be present in amounts of from 2~ 3 about 0 to about 70% by weight of dry cement.
Lightening agents such as pozzolana, fly ash, silica glass or ceramic microspheres and the like also may be uti-lized in amounts up to about 50% by weight of dry cement.
Silica may be present in amounts of from about 0 to 50%
by weight of cement and preferably from about 0 to 35% by weight of cement when a slurry with improved strength at elevated temperatures is desired. Preferably, the silica has a particle size in the range of less than about 40 mesh on the U. S. Sieve Series.
The composition of the present invention may be utilized in formations having bottom hole circulating temperatures of from about 30F. to in excess of about 450F.
The composition of the present invention may be prepared in accordance with any of the well known mixing techniques so long as the latex and surfactant are not directly admixed without prior dilution by other liquids present. In one preferred method, the water is introduced into the cement blender and the defoamer, if present, surfactant and latex then are sequentially added with suitable agitation to disperse the constituents. Any other liquid additives then may be admixed with the slurry.
Thereafter, the cement and any other dry solids are added to the blender and agitated for a sufficient period to admix the constituents. The amount of each constituent of the cement composition utilized in ~orming the cement slurry will depend upon the temperature level to be experienced, rheological considerations and the other additives that are present.
The cementing compositions of the present invention are useful in subterranean formation cementing operations and particularly oil, gas and water well cementing operations since the compositions have reduced fluid loss to the surrounding formation. The reduced fluid loss substantially maintains the hydraulic head of the cement column in the wellbore whereby gas migration into the wellbore from the surrounding formation is minimized or substantially pre-vented. The cement is utilized by introducing the cement composition into the space between the conduit or casing placed in the wellbore and the face of the wellbore penetrating the subterranean formation.
To illuctrate the unique benefits of the composition and method of the present invention and not by way of limita-tion, the following examples are presented.
EXAMPLE I
The following tests were performed to determine the uti-lity of the composition of the present invention.
Test slurries were prepared by admixing the liquid addi-tives one at a time with water in a blender. Each liquid additive was mixed for 20 seconds at 4000 RPM before the next additive was introduced. Thereafter, the dry additives were admixed with the liquid in the blender within 5 seconds while mixing at 4000 RPM and then the blender was operated at 12000 RPM for 35 seconds as per the procedures specified in API Spec 10, Fourth Ed August 1, 1988, in the API
Specification For Materials And Testing For Well Cements, ~ Q ~

which is incorporated herein by reference, to form a cement slurry test sample.
Thickening time testing, when performed, was in accor-dance with the procedures set forth in API Spec 10.
Rheological properties, when determined, were determined in accordance with the procedures outlined in API Spec 10.
In general, the cement sample was placed in an atmospheric consistometer which was preheated to the test temperature and stirred for 20 minutes. The atmospheric consistometer in a nonpressurized device that simulates a cement pumping process via movement of a consistometer can about a paddle.
The temperature of the test may be varied. The consistency of the cement is measured in terms of Bearden units of con-sistency (Bc). A pumpable cement slurry should measure in the range of from about 2-30 Bc and preferably from about 2 to 12-15 Bc. Cement slurries thicker than these ranges become progressively more difficult to mix and pump.
Slurries thinner than 3-5 Bc will tend to exhibit unde-sirable particle settling and free water generation.
Fluid loss is measured at 1000 psi through a 325 mesh screen on the U.S. Sieve Series in cc/30 minutes as more fully described in API Spec 10.
Solids suspension capability, when determined, requires the prior performance of the above-identified thickening time testing for the cement slurry sample. In general, after the thickening time for the cement slurry has been determined, a second test is initiated in the same equipment using the appropriate temperature and heating rate schedule.

When the schedule specified time to reach final test tem-perature and pressure has been reached plus 15 minutes, the slurry viscosity in consistency units is noted and the slurry cup drive motor is turned off for 10 minutes. The final temperature and pressure are maintained throughtout the remainder of the test. At the end of the 10 minute sta-tic period the slurry cup drive motor is turned on and the maximum viscosity when movement begins is noted in con-sistency units. After the test time has reached 50% of the cement slurry's thickening time as previously determined, the slurry cup drive motor is shut off again for 10 minutes and the viscosity is noted. At the end of 10 minutes, the slurry cup drive motor is started and the maximum viscosity when movement begins is noted. The slurry then is stirred until the test time has reached 75% of the cement slurry's thickening time. After which the drive motor is again stopped and the viscosity is noted. After 10 minutes the motor is restarted and the maximum viscosity is noted and the motor is then shut off and the slurry is cooled as quickly as possible in the consistometer to 194F., if at a temperature above 194F., while it is maintained in a static condition. If the shear pin on the drive motor shears off at any time, the test is terminated. The pressure then is released from the slurry cup and the sample is inspected for excessive settling by pushing a rod to the bottom of the test chamber to locate the level of settled solids. If excessive resistance is encountered in pushing the rod through the sample, the rod will not go through the sample or the shear pin sheared prior to completion of the three st:atic test periods, the cement slurry is considered to exhibit too much solids separation and is unacceptable for use. A small amount of light settling or fluid separation at the top of the sample cup is acceptable in most situations and would not effect performance of the cement slurry when introduced into a subterranean formation. The results of the various tests are set forth below:
The quantities set forth in percent are percent by weight of a 94/lb sack of cement. The quantities in gallons are gallons per 94/lb sack of cement.
Slurry Composition 1 Class H cement, 35% SSA-2 1., 60% hematite, 0.1% CMHEC 2-, 0.05 gal D-Air 3 3 , 0.143 gal. CFR-2L 4 , 0.3 gal HRo-l2L 5 , 3 gal. 25/75 styrene/butadiene latex, 0.338 gal. surfactant (35% active), 2.55 gal. water. Slurry weight 18.5 lb/gal.
Slurry Composition 2 Class H cement, 35% SSA-2, 60% hematite, 0.2% CMHEC, 0.05 gal D-Air 3, 0.143 gal. CFR-2L, 0.27 gal. HRo-l2L~ 2 gal.
25/75 styrene/butadiene latex , 0.23 gal. surfactant, 3.68 gal. water. Slurry weight 18.5 lb/gal.
Slurry Composition 3 Class H cement, 35% SSA-l 6-, 60% hematite, 0.15% CMHEC, 0.05 gal. D-Air 3, 1~ SCR-100 7 , 0.18 HRo-l3L 8-, 2.5 gal. 25/75 styrene/butadiene latex , 0.25 gal. surfactant, 3.37 gal.
water. Slurry weight 18.5 lb/gal.
Slurry Composition 4 Class H cement, 35% SSA-2, 60% hematite, 0.3% CMHEC, 0.05 --17-- ~J ~ ? ` ~
gal. D-AIR 3, 0.143 gal. CFR-2L, 0.32 gal. HR~-12L, 2.5 gal. 25/75 styrene/butadiene latex, 0.2 gal. surfactant, 3.17 gal. water. Slurry weight 18.5 lb/gal.
Slurry Composition 5 Class H cement, 35% SSA -1, 60% hematite, 0.15% CMHEC, 0.05 gal. D-AIR 3, 0.143 gal. CFR 2-L, 0.3 gal. HR~-12L, 2.5 gal. 25/75 styrene/butadiene latex, 0.25 gal. surfactant, 3.14 gal. water. Slurry weight 18.5 lb/gal.
Slurry Composition 6 Class H cement, 35% SSA-l, 60% hematite, 0.15% CMHEC, 0.05 gal. D-AIR 3, 1% SCR-100, 0.16 gal. HRO-13L, 2.5 gal. 25/75 styrene/butadiene latex, 0.25 gal. surfactant, 3.39 gal.
water. Slurry weight 18.5 lb/gal.
Slurry comPosition 7 Class H cement, 35% SSA-l, 60% hematite, 0.15% CMHEC, 0.05 gal. D-AIR 3, 2.0% SCR-100, 0.38 gal. HR~-13L, 2.4 gal 25/75 styrene/butadiene latex, 0.25 gal. surfactant, 2.96 gal water. Slurry weight 18.7 lb/gal.
Slurry Composition 8 Class H cement, 35% SSA-l, 60% hematite, 0.15% CMHEC, 0.05 gal. D-AIR 3, 2.0% SCR-100, 0.32 gal. HRo-l3L~ 2.5 gal.
25/75 styrene/butadiene latex, 0.25 gal. surfactant, 3.0 gal. water Slurry weight 18.7 lb/gal.
Slurry Composition 9 Class H cement, 35% SSA-l, 60% hematite, 0.15% CMHEC, 0.05 gal. D-AIR 3, 2.0% SCR-100, 0.28 gal. HR~-13L, 2.5 gal 25/75 styrene/butadiene latex, 0.25 gal. surfactant, 3.29 gal.
water. Slurry weight 18.5 lb/gal.

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Slurry Composition 10 Class H cement, 35% SSA-l, 60% hematite, 0.15% CMHEC, 0.05 gal. D-AIR 3, 1% SCR-100, 0.35 gal. HR~-13L, 2.5 gal 25/75 styrene/butadiene latex, 0.25 gal surfactant, 3.24 gal.
water. Slurry weight 18.5 lb/gal.
Slurry Composition 11 Class H cement, 35% SSA-l, 60% hematite, 0.15% CMHEC, 0.05 gal. D-AIR 3, 2.0% SCR-100, 0.5 gal HR~-13L, 2.5 gal 25/75 styrene/butadiene latex, 0.3 gal surfactant, 3.07 gal.
water. Slurry weight 18.5 lb/gal.

1. SSA-2 : graded silica sand 40-200 mesh 2. CMHEC : carboxymethylhydroxyethyl cellulose . D-AIR 3 : commercially available defoamer from HALLIBURTON SERVICES, Duncan, Oklahoma 73536 . CFR-2L : naphthalene sulfonic acid condensed with for-maldehyde (33% active) . HRo 12L : high temperature lignosulfonate retarder commer-cially available from HALLIBURTO~ SERVICES, Duncan, Oklahoma 73536 6. SSA-l : graded silica sand 140-400 mesh . SCR-100 : AMPSO/acrylic acid copolymer retarder commer-cially available from HALLIBURTON SERVICES, Duncan, Oklahoma 73536 . HR~-13L : high temperature lignosulfonate retarder commercially available from HALLIBURTON
SERVICES, Duncan, Oklahoma 73536 1~ 1 I .
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The following test was performed to determine the acid resistance of the cement slurry formed in accordance with the present invention.
Test slurries were prepared as in Example I. A sample of the slurry was placed in a 2 x 2 x 2 inch mold and allowed to cure for 96 hours at 200F. The cube then was removed from the mold, weighed and placed in a solution of 12% HCl/
3% HF maintained at 190F. for l hour. The percentage (~) of mass lost from the cube then was determined. The slurries utilized and the results of the tests are set forth below:
Slurry Composition l Class H cement, 5% Microbond HT l-, 2% bentonite, 0.5% CFR-3 2-, 0.3 gal surfactant, 0.2 gal D-AIR 3, 2 gal 25/75 styrene/butadiene latex, 3.7 gal water.
Slurry Composition 2 Class H cement, 5% Microbond HT, 2% bentonite, 0.5% CFR-3, 0.1% HR-5 3-, 0.3 gal surfactant, 0.2 gal D-AIR 3, 2 gal 25/75 styrene/butadiene latex, 3.7 gal water.

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Slurry weight of each sample 15.3 lb/gal.

Fluid loss at thickening Mass loss 4 day Slurry 175F., 1000 time 190F compressive No. (cc / 30 min) (hr:min) (% by wt.) strength (psi) 1 31 2:58 4.0 32004-2 - 5:37 0.0 3470 1. Microbond HT : cement expansion additive commercially available from HALLIBURTON SERVICES, Duncan, Oklahoma 73536 2. CFR-3 : cement dispersant additive commercially available from HALLIBURTON SERVICES, Duncan, Oklahoma 73536 3. HR~-5 : sodium lignosulfonate retarder commer-cially available from HALLIBU~TON
SERVICES, Duncan, Oklahoma 73536 4. : Strength obtained after acidizing treatment The foregoing test results clearly indicate the effec-tiveness of the fluid-loss control achieved by the com-position of the present invention.
EXAMPLE II
While that which is considered to be the preferred embo-diment of the invention has been described herein, it is to be understood that modifications and changes can be made in the composition and methods of the present invention without departing from the spirit or scope of the invention as set forth in the following claims.

Claims

1. Cement slurry compositions having improved fluid-loss control properties comprising:
hydraulic cement;
from about 4 to about 35% by weight of dry cement of a styrene(10-90% by weight) / butadiene (90-10% by weight) copolymer latex;
from about 5 to about 40% by weight of latex of a sur-factant of the general formula R (OR')n SO3 X
wherein X is any compatible cation, R is selected from the group consisting of C1 - C30 alkyl, C5 - C6 cycloalkyl, C1 - C4 alkyl substituted C5 - C6 cycloalkyl, phenyl, alkyl substituted phenyl of the general formula (R")a Ph - wherein Ph is phenylene and R" is C1 - C18 alkyl and a is an integer of from 1 to 3, phen(C1 - C18) alkyl and C1 - C18 alkyl substituted phen (C1 - C18) alkyl having a total of from about 8 to 28 carbon atoms, R' is a substituted ethylene group -CH2 - CH(R''') wherein R''' is independently selected from the group consisting of hydrogen, methyl and ethyl and n is a number from 0 to 40 provided that when R is phenyl or alkyl substituted phenyl n is at least 1; and

2. The composition of claim 1 wherein the surfactant is present in an amount of from about 10 to 25% by weight of latex.

3. The composition of claim 1 wherein the latex is present in an amount of from about 15 to about 25% by weight of dry cement.

4. The composition of claim 1 wherein the ratio of styrene/butadiene is in the range of from about 20/80 to about 80/20

5. The composition of claim 1 wherein the ratio of styrene/butadiene is in the range of from about 20/80 to about 30/70.

6. The composition of claim 1 defined further to include a copolymer of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid in a mole ratio having about 40 to about 60 mole percent 2-acrylamido-2-methylpropanesulfonic acid with the balance comprising acrylic acid or salts thereof.

7. The composition of claim 6 wherein said copolymer of 2-acrylamido-2-methylpropane sulfonic acid and acrylic acid has a molecular weight below about 5000.

8. The composition of claim 7 wherein said copolymer of 2-acrylamido-2methylpropanesulfonic acid and acrylic acid is present in an amount of from about 0.05 to 3% by weight of dry cement.

9. The composition of claim 6 defined further to include silica.

10. The composition of claim 1 defined further to include silica present in an amount of from about 0 to about 50%
by weight of dry cement.

11. The composition of claim 10 wherein said surfactant is of the general formula H(CH2)d (OCH2CH2)e SO3 X
wherein X is any compatible cation, d is in the range of from about 5 to 20 and e is in the range of from about 10 to 30.

12. The composition of claim 11 wherein the surfactant has an average value for d of about 12 to 15, an average value for e of about 15 and X is sodium.

13. A method of cementing a conduit in a subterranean for-mation containing gas comprising:
preparing a cement slurry by admixing (a) hydraulic cement, (b) from about 4 to about 35% by weight of dry cement of a styrene(10-90% by weight)/butadiene (90-10%
by weight) copolymer latex, (c) from about 5 to about 40% by weight of latex of a surfactant of the general formula R (OR')n SO3 X
wherein X is any compatible cation, R is selected from the group consisting of C1 - C30 alkyl, C5 - C6 cycloalkyl, C1 - C4 alkyl substituted C5 - C6 cycloalkyl, phenyl, alkyl substituted phenyl of the general formula (R")a Ph wherein Ph is phenylene and R" is C1 - C18 alkyl and a is an integer of from 1 to 3, phen(C1 - C18) alkyl and C1 - C18 alkyl substituted phen (C1 - C18) alkyl having a total of from about 8 to 28 carbon atoms, R' is a substituted ethylene group - CH2 - CH(R''') wherein R''' is independently selected from the group consisting of hydrogen, methyl and ethyl and n is a number from 0 to 40 provided that when R is phenyl or alkyl substituted phenyl n is at least 1; and water in an amount of from about 20 to about 150% by weight of dry cement and (d) water in an amount of from about 20 to about 150% by weight of dry cement;

introducing the cement slurry into the subterranean for-mation in a manner whereby the slurry is caused to surround the exterior surface of the conduit and substantially prevent migration of gas into the slurry through control of fluid-loss; and permitting the cement slurry to set whereby a bond is formed between the conduit and the formation without gas from the formation creating channels in the set cement.

14. The method of claim 13 wherein the surfactant is present in an amount of from about 10 to about 25% by weight of latex.

15. The method of claim 13 wherein the cement slurry is defined further to include a copolymer of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid in a mole ratio having about 40 to about 60 mole percent 2-acryl-amido-2-methylpropanesulfonic acid with the balance comprising acrylic acid or salts thereof.

16. The method of claim 15 wherein said copolymer of 2-acryl amido-2-methylpropanesulfonic acid and acrylic acid has a molecular weight below about 5000.

17. The method of claim 13 wherein the cement slurry is refined further to include silica present in an amount of from 0 to about 50% by weight of dry cement.

18. The method of claim 13 wherein said surfactant is of the general formula H (CH2)d (OCH2CH2)e SO3 -X+

wherein X is any compatible cation, d is in the range of from about 5 to 20 and e is in the range of from about 10 to 40.

19. The method of claim 13 wherein the surfactant is present in an amount of from about 10 to about 25% by weight of latex.