Fluid loss additives for well cementing compositions containing a tetrapolymer
This application is a divisional of application Ser. No. 07/414,961filed Sep. 28, 1990 now abandoned which was a continuation-in-part of application Ser. No. 07/029,029, filed Mar. 23, 1987, now abandoned. 
    
    
     The present invention pertains to cement additives which are useful for preventing water loss from cement slurries. Another aspect of the invention relates to novel tetrapolymers and the use of said novel tetrapolymers as cement additives. Another aspect of the invention relates to cement slurries which have improved water loss properties. A still further aspect of the invention relates to an improved process for cementing oil and gas wells. 
     BACKGROUND OF THE INVENTION 
     Cement compositions are used in the oil and gas industry to cement the annular space in the well bore between the surrounding formation and the pipe or casing. Typically, the cement slurry is pumped down inside the casing and back up the outside of the casing through the annular space. The amount of water which is used in forming the cement slurry will vary depending upon the type of hydraulic cement selected and the job conditions at hand. The amount of water used can vary over a wide range, depending upon such factors as the required consistency of the slurry and upon the strength requirement for the particular job. 
     Many times the hydraulic cement must be placed within or next to a porous medium, for example, shale strate encountered in the well bore. When this happens, water tends to filter out of the slurry and into the strata during the settling of the cement. Many difficulties are related to an uncontrolled fluid loss of this type, such as uncontrolled setting rate, improper placement of the slurry, impaired strength properties, and contamination of the surrounding strata. These conditions are all undesirable in oil and gas well cementing operations. 
     In order to lessen the loss of fluid from the aqueous cement slurry, various materials have been employed in the past. Unfortunately, these materials often have adverse effects upon the cement itself. 
     For example, U.S. Pat. No. 4,015,991 teaches the use of a copolymer of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid as a fluid loss additive for cement slurries. Although this copolymer will reduce the fluid loss from cement slurries, it also has the undesirable effect of reducing the compressive strength of the cement and of retarding the rate at which the cement forms a solid. 
     A further problem with the fluid loss additives currently available is their ineffectiveness at temperatures in the range of 300° F. to 450° F. For example, the copolymer described in U.S. Pat. No. 4,015,991 is ineffective at a temperature in excess of 250° F. 
     Thus, it would be a valuable contribution to the art to develop additives which would reduce water loss from cement slurries without having adverse effects upon the compressive strength of the cement or the rate at which the cement solidifies. 
     It would also be a valuable contribution to the art to develop additives which would reduce the water loss from cement slurries at elevated temperatures. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide additives which will reduce the water loss from cement slurries without reducing the compressive strength of the cement or delaying the rate at which the cement solidifies. 
     It is a further object of the present invention to provide additives that will prevent the loss of water from cement slurries at elevated temperatures. 
     It is a further object of the present invention to provide a method for reducing the loss of water from cement slurries without reducing the compressive strength of the cement or delaying the rate at which the cement solidifies. 
     It is yet another object of the present invention to provide a method for reducing the loss of water from cement slurries at an elevated temperature. 
     It is also an object of the present invention to provide cement compositions having improved water loss properties at elevated temperatures. 
     It is yet a further object of the present invention to provide an improved method for cementing oil and gas wells. 
     It is additionally an object of the present invention to provide water soluble polymer compositions which provide improved water loss properties in cement compositions. 
     In accordance with one embodiment of the present invention I have discovered that the addition of tetrapolymers to a cementing composition will reduce the water loss from said cementing composition. 
     In accordance with another embodiment of the present invention, I have discovered that an additive comprising (A) a tetrapolymer, (B) an electrolyte, (C) a base, (D) at least one surfactant, and (E) water, will reduce the water loss from cement slurries without reducing the compressive strength of the cement or delaying the rate at which the cement solidifies. It has also been discovered that this additive will control the water loss from cement slurries at elevated temperatures. 
     In an additional embodiment of the present invention it has also been discovered that tetrapolymers made in a highly energetic polymerization process provides improved water loss control. 
     DETAILED DESCRIPTION 
     As used in this application the term tetrapolymer refers to the polymerization product of at least a four monomer component polymerization. The four monomer components suitable for the practice of the present invention are: 
     Component A which has the formula ##STR1## wherein R 1  is hydrogen or methyl, R 2  is an alkyl amide containing C 2  -C 16  alkylene group, an alkyl containing C 1  -C 16  carbon atoms, benzyl, or alkyl benzyl containing C 7  -C 16  carbon atoms and Me is hydrogen, lithium, sodium or potassium; 
     Component B which has the formula ##STR2## wherein R 3  is hydrogen, methyl, or ethyl, R 4  is hydrogen, methyl, or ethyl or R 3  and R 4  form a cyclic amide; 
     Component C which has the formula ##STR3## wherein R 5  is hydrogen or methyl, and R 6  and R 7  are independently hydrogen, methyl, ethyl or propyl; and 
     Component D, which has the formula ##STR4## wherein R 8  is hydrogen or methyl and R 9  is a carboxylic acid, carboxylic salt, ester of a carboxylic acid, sulfonic acid, sulfonate or nitrile. 
     Suitable examples of component A include but are not limited to compounds selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid, salts of 2-acrylamido-2-methylpropanesulfonate, alkyvinyl sulfonic acids, alkyl vinyl sulfonates, vinyl benzene sulfonic acids, vinyl benzene sulfonates, alkyl vinyl benzene sulfonic acids, alkyl vinyl benzene sulfonates, and combinations of two or more thereof. 
     Suitable examples of monomer component B include but are not limited to compounds selected from the group consisting of N-vinyl acetamide, N-vinyl-N-methyl acetamide, N,N-dimethyl acetamide, N-vinyl-2-pyrrolidone, N-ethenyl-N-alkyl acetamide, and combinations of two or more thereof. 
     Suitable examples of monomer component C include but are not limited to ethylenically unsaturated N-substituted carboxylic acids selected from the group consisting of acrylamide, methyl acrylamide methylmethacryamide, N-alkylmethacrylamide, N,N-dialkylmethacrylamide, N-alkylacrylamide, N,N-dialkylacrylamide, and combinations of any two or more thereof. 
     Suitable examples of monomer component D include but are not limited to compounds selected from the group consisting of acrylic acid, salts of acrylic acid, methacrylic acid, salts of methacrylic acid, itaconic acid, salts of itaconic acid, acrylonitrile, alkoxy esters of acrylic acid, alkoxy esters of methacrylic acid, vinyl sulfonate, vinyl sulfonic acid and combinations of any two or more thereof. 
     As used in this application, the term tetrapolymer broadly refers to a water soluble polymer which is composed of a) from 1 to 60 weight percent of component B, b) from 1 to 60 weight percent of component C, c) from 10 to 90 weight percent of component A, and d) from 1 to 60 weight percent of component D. 
     One preferred tetrapolymer contains from 30 to 40 weight percent of N-vinyl-2-pyrrolidone, from 5 to 15 weight percent of acrylamide, from 50 to 60 weight percent of sodium 2-acrylamido-2-methylpropane sulfonate, and from 1 to 10 weight percent of acrylic acid. 
     Currently the preferred tetrapolymer composition comprises a) from about 10 to about 61 weight percent of monomer component A; b) from about 10 to about 60 weight percent of monomer component B; c) from about 3 to about 60 weight percent of monomer component C; and d) from at least 10 to about 55 weight percent of component D. Additionally, for specific applications in fresh water and brine water, the following monomer component ratios are recommended: 
     
         ______________________________________                                    
       Monomer Monomer   Monomer   Monomer                                
       Component                                                          
               Component Component Component                              
       A       B         C         D                                      
______________________________________                                    
Fresh Water                                                               
125° F.                                                            
Broad Range                                                               
         10-55     10-40      5-60   10-55                                
Preferred                                                                 
         20-38     20-30     23-35   14-20                                
Range                                                                     
200° F.                                                            
Broad Range                                                               
         10-55     10-30     15-45   10-20                                
Preferred                                                                 
         28-38     20-25     23-34   14-15                                
Range                                                                     
300° F.                                                            
Broad Range                                                               
         10-55     10-30      3-60   10-55                                
Preferred                                                                 
         27-55     10-30      5-35   10-55                                
Range                                                                     
Brine Water                                                               
200° F.                                                            
Broad Range                                                               
         10-55     10-30     15-60   10-30                                
Preferred                                                                 
         15-45     20-30     20-45   10-20                                
Range                                                                     
______________________________________                                    
 
    
     The currently most preferred tetrapolymer composition comprises a) from about 15 to about 45 weight percent of monomer component A; b) from about 10 to about 30 weight percent of monomer component B; c) from about 20 to about 45 weight percent of monomer component C; and d) from about 10 to about 20 weight percent of monomer component D. This particular tetrapolymer composition is believed to provide the best water loss control of any water loss control polymer tested to date. Tetrapolymers of this composition show extremely good water loss control over a broad range of temperatures in fresh water and brine solutions. The preferred monomers for making this tetrapolymer composition are a) 2-acrylamido-2-methylpropane sulfonic acid, sodium 2-acrylamido-2-methylpropane sulfonate or, b) N-vinyl-2-pyrrolidone; c) acrylamide; and d) sodium acrylate or acrylic acid. 
     The tetrapolymers of the present invention can be prepared by polymerization in accordance with any of the well known free radical techniques in solution, suspension or emulsion environment. See, for example, U.S. Pat. No. 3,547,899, or European patent application No. 0115836. In addition, other methods of polymerization known to one skilled in the art may be employed. 
     Preferred for the practice of the present invention is the polymerization of the four monomer components in a highly energetic polymerization process wherein a significant excess of initiation energy is provided by chemical or electromagnetic means including electrons, gamma rays, x-rays, slow neutrons and ultra violet radiation. The utilization of excess initation energy appears to result in the formation of consistently better tetrapolymers for use in water loss control. By way of guidance but in no way limiting to the present invention it has been found that a 100 percent excess of a chemical initator such as 2,2&#39;azobis(N,N&#39;-dimethylene isobutyramidine) dihydrochloride is effective to produce tetrapolymers with improved water loss control. 
     The molecular weight of the tetrapolymers of the present invention may be varied over a considerable range. The molecular weight may be as low as 30,000 or as high as 1,000,000 or more. 
     In one embodiment of the present invention I have discovered that tetrapolymers alone or in combination with other additives is very effective as a water loss control additive. The tetrapolymers disclosed in this invention are in fact so effective that when provided alone in an effective amount for hydraulic cements, a tetrapolymer may be the only additive required for water loss control. When utilized as a water loss control additive in hydraulic cements the tetrapolymer should be employed in an amount ranging from about 0.1 weight percent to about 5 weight percent by weight of dry hydraulic cement, preferably the tetrapolymer will be employed in an amount ranging from about 0.2 weight percent to about 2 weight percent by weight of dry hydraulic cement. The weight ranges specified above may be optimized for the particular cement and conditions under which it is utilized. 
     The monomer ratios as specified above for Fresh Water and Brine Water (at various temperatures) are particularly preferred in cement slurries which will be subjected to conditions similar to those specified above. 
     Additionally, it has been discovered that an additive comprising (A) a tetrapolymer, (B) an electrolyte, (C) a base, (D) at least one surfactant, and (E) water, will reduce the water loss from cement slurries without reducing the compressive strength of the cement or delaying the rate at which the cement solidifies. It has also been discovered that this additive will control the water loss from cement slurries at elevated temperatures. 
     Suitable electrolytes (B) for use in the present invention can be selected from the group consisting of sodium, potassium, lithium, or ammonium salts of chlorine, bromine, iodine, nitrate, or fluorine. At the present time, the preferred electrolyte is potassium chloride. 
     Suitable bases (C) for use in the present invention include those selected from the group consisting of potassium hydroxide, sodium hydroxide, or ammonium hydroxide. The presently preferred base is potassium hydroxide. 
     Suitable (D) surfactants for use in the present invention can be selected from the group consisting of: 
     1) carboxylates of the formula 
     
         RCOO.sup.- M.sup.+ 
    
      wherein R is selected from the group consisting of alkyl groups containing from 9 to 21 carbon atoms and M is selected from the group consisting of sodium, potassium, or lithium; 
     2) polyalkoxycarboxylates represented by the formula ##STR5##  wherein R is selected from the group consisting of alkyl and alkylaryl groups containing from 10 to 21 carbon atoms, M is selected from the group consisting of sodium, lithium or potassium, and n is an integer from 5 to 21; 
     3) sulfonates of the formula 
     
         R SO.sub.3.sup.- M.sup.+ 
    
      wherein R is selected from the group consisting of alkyl groups containing from 10 to 20 carbon atoms, and M is selected from the group consisting of sodium, potassium, or lithium; 
     4) alkylbenzene sulfonates represented by the formula 
     
         RC.sub.6 H.sub.4 SO.sub.3.sup.- M.sup.+ 
    
      wherein R is selected from the group consisting of alkyl groups containing from 10 to 20 carbon atoms, and M is selected from the group consisting of sodium, lithium, or potassium; 
     5) lignosulfonates; 
     6) naphthalene sulfonates of the formula 
     
         RC.sub.10 H.sub.6 SO.sub.3.sup.- M.sup.+ 
    
      wherein R is selected from the group consisting of alkyl groups containing from 3 to 10 carbon atoms, and M is selected from the group consisting of sodium, lithium, calcium or potassium; 
     7) naphthalene sulfonates which have been condensed with formaldehyde; 
     8) the alpha-olefin sulfonates of the formula 
     
         RC═CHSO.sub.3.sup.- M.sup.+ 
    
      wherein R is selected from the group consisting of alkyl groups containing from 10 to 20 carbon atoms and M is selected from the group consisting of potassium, sodium or lithium; 
     9) poly(ethylene glycol) monomethyl ethers of the formula 
     
         HO--(CH.sub.2 CH.sub.2 O).sub.x CH.sub.3 
    
      wherein x can vary from about 20 to about 225,000. 
     10) polyethylene glycols of the formula 
     
         HO(CH.sub.2 CH.sub.2 O).sub.x H 
    
      wherein x can vary from about 20 to about 225,000. 
     11) alcohol ethoxylates of the formula 
     
         R[OCH.sub.2 CH.sub.2 ].sub.n OH 
    
      wherein R is selected from the group consisting of alkyl groups containing from 6 to 20 carbon atoms and n is an integer from 2 to 100; 
     12) alkylphenyl ethoxylates of the formula 
     
         RC.sub.6 H.sub.4 (OC.sub.2 H.sub.4).sub.n OH 
    
      wherein R is selected from the group consisting of alkyl groups containing from 8 to 15 carbon atoms and n is an integer from 2 to 70; and 
     13) petroleum sulfonates. 
     All of these surfactants as well as their methods of preparation are well known to those skilled in the art. They are available from numerous commercial suppliers. 
     At the present time it is preferred that the cement slurry water loss additive contain two surfactants. 
     One of the preferred surfactants is poly(ethylene glycol) monomethyl ether. The surfactant will have a molecular weight ranging from about 200 to about 8000, preferably 200 to 1000. Presently Dow Froth 1012® with molecular weight of about 385 is the most preferred. 
     The other preferred surfactant is a naphthalene sulfonate formaldehyde condensate. Such compounds are also known as sulfonated condensation products of formaldehyde and naphthalene or metal salts of condensation produces of naphthalene sulfonic acid with formaldehyde. 
     Condensed naphthalene sulfonate formaldehyde condensates suitable for use in the present invention are marketed by a number of companies under various brands and the preparation of some of these are set forth, for example, in U.S. Pat. Nos. 3,537,869 or 4,814,887. Examples of commercially available naphthalene sulfonate formaldehyde condensates are Lomar D®, CFR-2® Tamol®, SM®, TIC®, and Daxad®. Currently Lomar D® is the preferred naphthalene sulfonate formaldehyde condensate. 
     At the present time, it is also preferred that the water loss additive contain (F), a preservative. The nature of the preservative is not critical to the practice of the present invention and any commercially available preservative is suitable for use in the present invention. At the present time, the preferred preservative is a paraformaldehyde. 
     The constituents of the water loss additive are present in the following quantities: 
     
         ______________________________________                                    
              Broad Range                                                 
                       Preferred Range                                    
              wt %     wt %                                               
______________________________________                                    
A   Tetrapolymer    0.1-70     1.5-10                                     
B   Electrolyte       0.1-37.2 2-10                                       
C   Base            0.1-3      .2-2                                       
D   Surfactant      0.1-40     5-15                                       
E   Water            29-95     70-80                                      
F   Preservative (optional)                                               
                    0.001-5                                               
______________________________________                                    
 
    
     The fluid additive of the present invention is suitable for use with any hydraulic cement. The term hydraulic cement is meant to encompass any organic cement that hardens or sets under water. Hydraulic cements, for example, include portland cements, aluminus and pozzolan cements, and the like. The term hydraulic cement is also intended to include cements having minor amounts of extenders such as bentonite, gilsonite, and is also intended to include cements used either without any appreciable sand or aggregate material or such cements admixed with a granular filling material such as sand, ground limestone, and the like. Thus, for example, any of the class A-J cements listed in API Spect 10, Section 2, First Ed., January, 1982, are suitable for this purpose. Strength enhancers such as silica powder can also be employed. 
     The dry hydraulic cement component, the fluid loss additive of the present invention, can be admixed dry or with water to form a pumpable, settable cement slurry. The cement slurry will set to form a monolithic solid. The water which is employed to form the cement slurry may be any naturally occurring water suitable for preparing cement slurries. Sea water may be employed and is thus convenient in offshore operations. It is a particular advantage of the fluid loss additive of the present invention that it is effective in reducing fluid loss from cement slurries even where brines are employed to make up the slurry. This constitutes another important advantage of the invention over many other cement additives known in the art. 
     The amount of water employed to make up the hydraulic cement slurry is not critical, and generally the amount of water necessary to give a settable cement composition having the required characteristics will be an amount from about 25 to about 150 percent by weight, based on the weight of the dry hydraulic cement. As discussed previously, the amount of water employed should be only such as is sufficient to produce a pumpable slurry. Use of the water loss additive of the present invention makes it unnecessary to add excess water in anticipation of substantial water losses. 
     Generally, the amount of fluid loss additive employed will be in the range of from 0.2 gal to 2.5 gal of additive per 94 lbs. of cement utilized in preparing the cement slurry. 
     The fluid loss additive of the present invention is suitable for use in cement slurries that are subjected to temperatures ranging from 80° F. to 450° F. 
     In the method of cementing a well bore with the present additive, a hydraulic cement, water and the fluid loss additive of the present invention are mixed together to form a pumpable slurry. The cement slurry so prepared is then pumped to the desired location in the well bore and allowed to harden to form a solid mass. 
    
    
     The following examples are intended to illustrate the advantages of this invention, but are not intended to unduly limit this invention. 
     EXAMPLE I 
     The purpose of this example is to demonstrate the composition of and a method for preparing the preferred fluid loss additive of the present invention. 
     The composition of the preferred fluid loss additive system of the present invention is represented below. 
     
                       TABLE I                                                     
______________________________________                                    
Material             Amount (wt in grams)                                 
______________________________________                                    
Water                78                                                   
KCI                  2                                                    
KOH                  1                                                    
Paraformaldehyde     0.02                                                 
Sodium naphthalene   9.8                                                  
formaldehyde condensate.sup.1                                             
Poly(ethylene glycol) monomethyl                                          
                     4                                                    
ether.sup.2                                                               
Tetrapolymer.sup.3   5                                                    
______________________________________                                    
 .sup.1 Lomar D ®, Diamond Shamrock                                   
 .sup.2 Dow Froth 1012 ®, Dow                                         
 .sup.3 a poly(sodium 2acrylamido-2-methylpropane                         
 sulfonateco-N-vinyl-2-pyrrolidone-co-acrylamide-co-acrylic acid),        
 containing 55 wt % sodium 2acrylamido-2-methylpropane sulfonate, 35 wt % 
 Nvinyl-2-pyrrolidone, 10 wt % acrylamide, 5 wt % acrylic acid and is     
 commercially available as HE ® polymer from Phillips Petroleum       
 Company.                                                                 
 
    
     A preferred manner of preparing this fluid loss additive is to mix the ingredients in the order listed under agitation. 
     EXAMPLE II 
     A series of cementing slurry compositions in accordance with the present invention and having the compositions as noted in Table II below were prepared by mixing the additive system of Example I with water and a Class H cement 1 . 
    
     
                       TABLE II                                                    
______________________________________                                    
                        Amount water loss in                              
Material      Amount    gal/sack of cement                                
______________________________________                                    
Cement A                                                                  
Class H cement                                                            
              829.85  gm    0.3  gal                                      
Water         313.5   ml                                                  
Water loss additive                                                       
              22.2    ml                                                  
Cement B                                                                  
Class H cement                                                            
              829.85  gm    0.41 gal                                      
Water         305.5   ml                                                  
Water loss additive                                                       
              30.3    ml                                                  
Cement C                                                                  
Class H cement                                                            
              829.85  gm    0.60 gal                                      
Water         285.5   ml                                                  
Water loss additive                                                       
              50.2    ml                                                  
Cement D                                                                  
Class H cement                                                            
              829.85  gm    0.68 gal                                      
Water         285.5   ml                                                  
Water loss additive                                                       
              50.1    ml                                                  
Cement E                                                                  
Class H cement                                                            
              829.85  gm    0.75 gal                                      
Water         280.42  ml                                                  
Water loss additive                                                       
              55.2    ml                                                  
Cement F (control)                                                        
Class H cement                                                            
              829.85  gm    0                                             
Water         335.7   ml                                                  
Cement G (control)                                                        
Class H cement                                                            
              850.96  gm    0                                             
Water         328.9   ml                                                  
Cement H                                                                  
Class H cement                                                            
              645.92  gm    0.41 gal                                      
Sand          226.1   gm                                                  
Water         284.35  ml                                                  
Water loss additive                                                       
              23.51   ml                                                  
Cement I                                                                  
Class H cement                                                            
              645.92  gm    0.60 gal                                      
Sand          226.1   gm                                                  
Water         273.46  ml                                                  
Water loss additive                                                       
              34.4    ml                                                  
Cement J                                                                  
Class H cement                                                            
              645.92  gm    0.75 gal                                      
Sand          226.1   gm                                                  
Water         264.86  ml                                                  
Water loss additive                                                       
              43.0    ml                                                  
Cement K                                                                  
Class H cement                                                            
              829.05  gm     .80 gal                                      
Water         275.8   ml                                                  
Water loss additive                                                       
              58.9    ml                                                  
Cement L                                                                  
Class H cement                                                            
              829.85  gm    1.00 gal                                      
Water         261.1   ml                                                  
Water loss additive                                                       
              73.7    ml                                                  
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     EXAMPLE III 
     To demonstrate that the water loss additive of the present invention will reduce the water loss from cement slurries over a broad range of temperatures; the water loss properties of cementing slurry compositions prepared as in Example II were determined in accordance with API Spec 10, Appendix F, First Ed., January 1982. 
     The following results were obtained. 
     
                       TABLE III                                                   
______________________________________                                    
        Concentration                                                     
        of Additive     Temp.   Fluid-Loss                                
Cement  (gal/94 lbs cement)                                               
                        °F.                                        
                                cc/30&#39;                                    
______________________________________                                    
B       0.41             80     66                                        
B       0.41            100     76                                        
D       0.68            100     40                                        
F (control)                                                               
        0.00            100     +1298                                     
B       0.41            125     74                                        
D       0.68            125     46                                        
F (control)                                                               
        0.00            125     +1298                                     
B       0.41            170     80                                        
D       0.68            170     46                                        
F (control)                                                               
        0.00            170     +1500                                     
H       0.41            170     78                                        
I       0.60            170     48                                        
H       0.41            200     118                                       
I       0.60            200     131                                       
I       0.60            230     138                                       
I       0.60            250     40                                        
J       0.75            300     54                                        
______________________________________                                    
 
    
     The water loss properties of cement slurries prepared without the additive of the present invention (cement F) were determined at temperatures ranging from 100° F. to 170° F. These cement slurries lost between 1298 to 1500 cc of fluid during the 30 minute testing period. 
     The water loss properties of cement slurries prepared with the additive of the present invention were determined at temperatures ranging from 80° F. to 300° F. These cements only lost from 40 to 138 cc of fluid during the 30 minute testing period. 
     Thus, this data demonstrates that the additive of the present invention provides cements with superior water loss properties over a broad temperature range. 
     EXAMPLE IV 
     To demonstrate that the fluid loss additive of the present invention does not decrease the compressive strength of the resulting cement composition, a series of cement compositions as prepared in Example II were tested in accordance with API Spec 10, Section 7, Compressive Strength Tests, First Ed., January 1982. 
     The following data was generated. 
     
                       TABLE IV                                                    
______________________________________                                    
Concen-        24 Hr COMMPRESSIVE                                         
tration        STRENGTH (PSI)                                             
of Additive    @ Atmospheric                                              
(gal/94 lbs    pressure     @ 3000 PSI                                    
Cement  of cement) 80° F.                                          
                            125° F.                                
                                  150° F.                          
                                         170° F.                   
______________________________________                                    
F (control)                                                               
        0.00       1483     3517  4646   4799                             
A       0.30       1483     3725  4697   4713                             
B       0.41       1508     3642  4689   5013                             
C       0.68       1550     3775  5847   6192                             
______________________________________                                    
 
    
     Cement F was prepared without the fluid loss additive of the present invention. It demonstrated a compressive strength of 1483 PSI at 80° F. during a 24 hour compressive strength test. 
     Cements A, B, and C were prepared with the fluid loss additive of the present invention. They demonstrated compressive strengths ranging between 1483 to 1550 PSI. Thus, the additive of the present invention does not decrease the compressive strength of cements. 
     A similar trend was demonstrated in the tests conducted at 125° F., 150° F., and 170° F. 
     EXAMPLE V 
     To demonstrate that the additive of the present invention will reduce the fluid loss from cement slurries which have been formulated with salt water, a cement slurry B&#39;, D&#39;, L&#39; and M&#39; were prepared as were Cements B, D, L, and M of Example II except that varying concentrations of salt water was used to prepare the cementing slurry. For comparative purposes a cement slurry F was prepared as in Example II. 
     The fluid loss properties of these cement slurries were determined in accordance with API Spec 10, Appendix F, First Ed., January, 1982. 
     The following results were obtained. 
     
                       TABLE V                                                     
______________________________________                                    
        Concentration                                                     
        of Additive   NaCL    Temp. Fluid-Loss                            
Cement  (gal/94 lbs cement)                                               
                      wt. %   °F.                                  
                                    cc/30&#39;                                
______________________________________                                    
F (control)                                                               
        0             0.0     100   +1298                                 
B&#39;      0.41          3.0      80   123                                   
B&#39;      0.41          10.0     80   134                                   
B&#39;      0.41          18.0     80   180                                   
B&#39;      0.41          37.2     80   68                                    
D&#39;      0.68          3       100   50                                    
D&#39;      0.68          3       125   48                                    
D&#39;      0.68          3       150   50                                    
D&#39;      0.68          3       175   53                                    
D&#39;      0.68          10      100   49                                    
D&#39;      0.68          10      125   46                                    
D&#39;      0.68          10      150   63                                    
D       0.68          10      175   66                                    
L&#39;      0.80          3       100   43                                    
L&#39;      0.80          3       125   45                                    
L&#39;      0.80          3       150   48                                    
L&#39;      0.80          3       175   42                                    
L&#39;      0.80          10      100   49                                    
L&#39;      0.80          10      125   52                                    
L&#39;      0.80          10      150   54                                    
L&#39;      0.80          10      175   56                                    
M&#39;      1.00          18      200   94                                    
M&#39;      1.00          37.2    100   104                                   
M&#39;      1.00          37.2    125   110                                   
M&#39;      1.00          37.2    150   122                                   
M&#39;      1.00          37.2    175   130                                   
M&#39;      1.00          37.2    200   146                                   
______________________________________                                    
 
    
     Cement F which was prepared without the additive of the present invention, exhibited a fluid loss in excess of 1298 cc during the 30 minute testing period. The cement slurries prepared with the fluid loss additive of the present invention only lost from 43 to 180 cc&#39;s during the 30 minute test period. Thus, the fluid loss additive of the present invention will reduce the water loss from cement slurries which have been formulated with salt water. 
     EXAMPLE VI 
     To demonstrate that the fluid loss additive of the present invention does not retard the rate at which the cement solidifies, cementing compositions were prepared as in Example II and the rate at which the cement thickens was determined in accordance with API, Spec 10, Section 8, First Ed., January, 1982. 
     The following results were obtained. 
     
                       TABLE VI                                                    
______________________________________                                    
       Concentration               Thickening                             
       of Additive                 Time.sup.1                             
       (gal/94 lbs  Temp.   API    (in hours)                             
Cement of cement)   (°F.)                                          
                            Schedule                                      
                                   70 Bc 100 Bc                           
______________________________________                                    
F      0.00          80     1g3    4:45  4:57                             
B      0.41          80     1g3    4:11  4:25                             
C      0.68          80     1g3    5:08  5:19                             
F      0.00         100     3g4    2:49  3:14                             
B      0.41         100     3g4    2:54  3:28                             
C      0.68         100     3g4    3:02  3:30                             
F      0.00         125     5g3    1:36  1:46                             
B      0.41         125     5g3    1:43  1:47                             
C      0.68         125     5g3    1:52  2:00                             
______________________________________                                    
 .sup.1 Variations of 30 minutes or less in thickening time is considered 
 within normal experimental error.                                        
 
    
     Cement F which does not contain the fluid loss additive of the present invention, thickened in 4 hours and 45 minutes when tested at 80° F. 
     Cements B and C which contained the additive of the present invention, thickened in 4 hours, 11 minutes; and 5 hours, 8 minutes; respectively. 
     Although at first glance it appears that the additive of the present invention retarded the rate at which Cement C solidified, this is not the case. 
     Due to the large amount of experimental error inherent in the testing procedures, cements which thicken within 30 minutes of each other are considered to have equivalent thickening rates. Therefore, the additive of the present invention does not delay the rate at which cement slurries solidify. 
     EXAMPLE VII 
     This example presents data on fluid loss in cements as performed according to conventional API cement tests. The tests were performed according to appendix F with well-simulation as outlined in paragraph d relative to atmospheric pressure simulation. The results are recorded in Table VII. 
     
                       TABLE VII                                                   
______________________________________                                    
API Water Loss in Fresh Water, cc/30 minutes                              
polymer composition                                                       
in weight %        125° F.                                         
ID No.                                                                    
      AM/NAc/AMPS/NVP  cc/30 min.                                         
                                 conc. added                              
______________________________________                                    
 1    3/15.5/61/20.5   275       0.24%                                    
 2    50/30/10/10      208       0.24%                                    
 3    37.1/18.2/33.1/11.1                                                 
                       413       0.24%                                    
 4    35/30/15/30      202       0.24%                                    
 5    15.6/9.4/25/50   738       0.24%                                    
 6    13.7/2.1/63.0/21.2                                                  
                       388       0.24%                                    
 7    5/55/30/10        77       0.24%                                    
 8    2/3/90/5         716       0.24%                                    
 9    5/20/15/60       376       0.24%                                    
10    55/20/15/10      102       0.24%                                    
11    60/10/10/20      148       0.24%                                    
12    45/25/10/20      136       0.24%                                    
13    45/20/15/20      108       0.24%                                    
14    45/10/25/20      128       0.24%                                    
15    35/10/35/20      135       0.24%                                    
16    30/10/40/20      114       0.24%                                    
17    30/15/35/20      110       0.24%                                    
18    26.6/16.0/42.4/15                                                   
                       118       0.24%                                    
19    25/15/40/20      114       0.24%                                    
20    60/20/10/10       88       0.24%                                    
21    35/15/30/20       88       0.24%                                    
22    34/14/30/22       82       0.24%                                    
23    33/14/28/25       91       0.24%                                    
24    32/13/27/28       86       0.24%                                    
25    23.5/14.0/37.5/25                                                   
                        90       0.24%                                    
26    5/55/30/10        77       0.24%                                    
______________________________________                                    
 Note:-                                                                   
 Concentration of polymer added in % by weight of cement (BWOC).          
 AM = acrylamide                                                          
 NAc = sodium acrylate                                                    
 AMPS ™ = acrylamidomethylpropane sulfonate (trademark of Lubrizol)    
 NVP = nvinylpyrrolidone                                                  
 
    
     This data indicates that these polymers are effective in reducing water loss in drilling cements. 
     EXAMPLE VIII 
     This example presents data on fluid loss in cements as performed according to conventional API cement tests. The tests were performed according to appendix F with well-simulation as outlined in paragraph D relative to atmospheric pressure simulation. The results are recorded in Table VIII. 
     
                       TABLE VIII                                                  
______________________________________                                    
API Water Loss in Fresh Water, cc/30 minutes                              
polymer composition                                                       
in weight %        200° F.                                         
ID No.                                                                    
      AM/NAc/AMPS/NVP  cc/30 min.                                         
                                 conc. added                              
______________________________________                                    
 1    15.6/9.4/25/50   728       0.33%                                    
 2    13.7/2.1/63.1/21.1                                                  
                       814       0.33%                                    
 3    2/3/90/5         717       0.33%                                    
 4    55/20/15/10      115       0.33%                                    
 5    50/30/10/10      132       0.33%                                    
 6    37.1/18.2/33.1/11.1                                                 
                       100       0.33%                                    
 7    35/30/15/30      100       0.33%                                    
 8    18.8/11.2/30/40  260       0.33%                                    
 9    5/20/15/60       153       0.33%                                    
10    5/55/30/10       103       0.33%                                    
11    45/10/25/20      52        0.33%                                    
12    60/20/10/10      56        0.33%                                    
13    60/10/10/20      76        0.33%                                    
14    50/20/10/20      77        0.33%                                    
15    35/15/30/20      50        0.33%                                    
16    32/13/27/28      55        0.33%                                    
17    30/10/40/20      53        0.33%                                    
18    26.6/16/42.4/15  52        0.33%                                    
19    25/10/45/20      54        0.33%                                    
20    25/15/40/20      50        0.33%                                    
21    25/20/35/20      57        0.33%                                    
22    20/15/45/20      56        0.33%                                    
23    20/10/50/20      54        0.33%                                    
24    15/10/55/20      58        0.33%                                    
25    3/15.5/61/20.5   97        0.33%                                    
26    34/14/30/22      46        0.33%                                    
27    33/14/28/25      46        0.33%                                    
28    30/15/35/20      47        0.33%                                    
29    23.5/14/37.5/25  45        0.33%                                    
30    35/10/35/20      54        0.33%                                    
31    32/13/27/28      55        0.33%                                    
32    45/25/10/20      56        0.33%                                    
______________________________________                                    
 Note:-                                                                   
 Cement slurries tested at 200° F. contain 35% silica sand BWOC (by
 weight of cement) and concentration of polymer added is in % BWOC.       
 AM = acrylamide                                                          
 NAc = sodium acrylate                                                    
 AMPS ™ = acrylamidomethylpropane sulfonate (trademark of Lubrizol)    
 NVP = nvinyl pyrrolidone                                                 
 
    
     This data indicates that these polymers are effective in reducing water loss in drilling cements. 
     EXAMPLE IX 
     This example presents data on fluid loss in cements as performed according to conventional API cement tests. The tests were performed according to appendix F with well-simulation as outlined in paragraph d relative to atmospheric pressure simulation. The results are recorded in Table IX. 
     
                       TABLE IX                                                    
______________________________________                                    
API Water Loss in Fresh Water, cc/30 minutes                              
polymer composition                                                       
in weight %        300° F.                                         
ID No.                                                                    
      AM/NAc/AMPS/NVP  cc/30 min.                                         
                                 conc. added                              
______________________________________                                    
 1    60/20/10/10      254       0.36%                                    
 2    55/20/15/10      259       0.36%                                    
 3    50/20/10/20      221       0.36%                                    
 4    45/25/10/20      227       0.36%                                    
 5    35/30/15/30      245       0.36%                                    
 6    15.6/9.4/25/50   1232      0.36%                                    
 7    13.6/2.1/63.1/21.2                                                  
                       1041      0.36%                                    
 8    5/20/15/60       1408      0.36%                                    
 9    2/3/90/5         1275      0.36%                                    
10    60/10/10/20      138       0.36%                                    
11    50/30/10/10      137       0.36%                                    
12    45/20/15/20      172       0.36%                                    
13    45/10/25/20      118       0.36%                                    
14    37.1/18.7/33.1/11.1                                                 
                       154       0.36%                                    
15    35/10/35/20      176       0.36%                                    
16    30/10/40/20      124       0.36%                                    
17    25/10/45/20      122       0.36%                                    
18    20/10/50/20      106       0.36%                                    
19    3/16/61/20       108       0.36%                                    
20    35/15/30/20       86       0.36%                                    
21    34/14/30/22       85       0.36%                                    
22    33/14/28/25       84       0.36%                                    
23    32/13/27/28       92       0.36%                                    
24    30/15/35/20       91       0.36%                                    
25    25/15/40/20       94       0.36%                                    
26    25/20/35/20       78       0.36%                                    
27    23.5/14.1/37.5/25                                                   
                        77       0.36%                                    
28    20/15/45/20       90       0.36%                                    
29    15/10/55/20       88       0.36%                                    
30    5/55/30/10        44       0.36%                                    
______________________________________                                    
 Note:-                                                                   
 Cement slurries tested at 300° F. contain 35% silica sand BWOC (by
 weight of cement) and concentration of polymer added is in % BWOC.       
 AM = acrylamide                                                          
 NAc = sodium acrylate                                                    
 AMPS ™ = acrylamidomethylpropane sulfonate (trademark of Lubrizol)    
 NVP = nvinyl pyrrolidone                                                 
 
    
     This data indicates that these polymers are effective in reducing water loss in drilling cements. 
     EXAMPLE X 
     This example presents data on fluid loss in cements as performed according to conventional API cement tests. The tests were performed according to appendix F with well-simulation as outlined in paragraph d relative to atmospheric pressure simulation. The results are recorded in Table X. 
     
                       TABLE X                                                     
______________________________________                                    
API Water Loss in 10% NaCl, cc/30 minutes                                 
polymer composition                                                       
in weight %        200° F.                                         
ID No.                                                                    
      AM/NAc/AMPS/NVP  cc/30 min.                                         
                                 conc. added                              
______________________________________                                    
 1    15.6/9.4/25/50   680       0.3%                                     
 2    13.6/2.1/63.1/21.2                                                  
                       1107      0.3%                                     
 3    5/55/30/10       1833      0.3%                                     
 4    2/3/90/5         1177      0.3%                                     
 5    60/10/10/20      238       0.3%                                     
 6    55/20/15/10      200       0.3%                                     
 7    50/30/10/10      212       0.3%                                     
 8    37/18/33/12      206       0.3%                                     
 9    3/15.5/61/20.5   272       0.3%                                     
10    60/20/10/10      192       0.3%                                     
11    50/20/10/20      150       0.3%                                     
12    45/25/10/20      102       0.3%                                     
13    35/10/35/20      115       0.3%                                     
14    35/30/15/30      148       0.3%                                     
15    30/10/40/20      109       0.3%                                     
16    30/15/35/20      119       0.3%                                     
17    27/16/43/15      120       0.3%                                     
18    25/10/45/20      106       0.3%                                     
19    20/10/50/20      118       0.3%                                     
20    15/10/55/20      120       0.3%                                     
21    45/20/15/20       98       0.3%                                     
22    45/10/25/20       92       0.3%                                     
23    35/15/30/20       96       0.3%                                     
24    34/14/30/22       64       0.3%                                     
25    33/14/28/25       72       0.3%                                     
26    32/13/27/28       80       0.3%                                     
27    25/15/40/20       80       0.3%                                     
28    25/20/35/20       96       0.3%                                     
29    23.5/14/37.5/25   84       0.3%                                     
30    20/15/45/20       88       0.3%                                     
______________________________________                                    
 Note:-                                                                   
 Concentration of polymer added in % by weight of cement (BWOC).          
  AM = acrylamide                                                         
 NAc = sodium acrylate                                                    
 AMPS ™ = acrylamidomethylpropane sulfonate (trademark of Lubrizol)    
 NVP = nvinyl pyrrolidone                                                 
 
    
     EXAMPLE XI 
     All polymers were prepared using a bulk solution polymerization with a free radical initiator in a stoichiometric excess (approximately 100% excess). The initator used was 2,2&#39;-azobis (N,N&#39;-dimethyleneisobutyramidine) dihydrochloride. The monomers were added in the desired weight percent ratio, with water being added to achieve the desired solids content. EDTA (ethylenediaminetetraacetic acid), a chelating agent, was also added in a stoichiomeric excess. The system was throughly purged with an inert gas, and the monomers were allowed to react at temperatures in the range of 20° to 60° C. 
     Reasonable variations can be made in view of the foregoing disclosure without departing from the spirit or scope of the present invention.