NZ331387A - Light weight high temperature well cement compositions and methods for use in the presence of carbon dioxide and brines at high temperature and pressure - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number 331 387 # New Zealand No. 331387 International No. PCT/ TO BE ENTERED AFTER ACCEPTANCE AND PUBLICATION Priority dates: 27.07.1998; Complete Specification Filed: 14.08.1998 Classification:^) B28C5/00; C04B38/00 Publication date: 29 April 1999 Journal No.: 1439 Title of Invention: Light weight high temperature well cement compositions and methods Name, address and nationality of applicant(s) as in international application form: HALLIBURTON ENERGY SERVICES, INC., a Delaware corporation of PO Box 1431, Duncan, Oklahoma 73533, United States of America NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION NEW ZEALAND PATENTS ACT, 1953 No: Date: COMPLETE SPECIFICATION LIGHT WEIGHT HIGH TEMPERATURE WELL CEMENT COMPOSITIONS AND METHODS [INTELLECTUAL HHUHfcHry OFFICE I I OF NZ I I M AUG JS98 I I RECElvgp I We, HALLIBURTON ENERGY SERVICES, INC., a Delaware Corporation, USA, of P O Box 1431, Duncan, Oklahoma 73533, USA, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: 1 (followed by page la) 33138 ,J< A'JS ££cg / 1998 BACKGROUND OF THE INVENTION 1. Field of the Invention.

The present invention relates generally to light weight high temperature well cement compositions and methods, and more particularly, to such compositions and methods which are suitable for cementing high temperature wells containing carbon dioxide. 2. Description of the Prior Art.

In the completion of high temperature subterranean wells containing carbon dioxide, eg., geothermal wells, the use of conventional hydraulic cement compositions often results in early well failure. Because of the high static well bore temperatures involved coupled with the presence of brines containing carbon dioxide, conventional hydraulic well cements rapidly deteriorate due to alkali carbonation, especially sodium carbonate induced carbonation. In geothermal wells which typically involve very high temperatures, pressures and carbon dioxide concentrations, conventional well cement failures have occurred in less than five years causing the collapse of the well casing.

It has heretofore been discovered that a cement material known as calcium phosphate cement formed by an acid-base ' office j 331387 I . EiVED I reaction between calcium aluminate and a pliUtlJJJlclLt!ll,lLUiiLuiiiiBg solution has high strength, low permeability and' excellent carbon dioxide resistance when cured in hydrothermal environments. However, calcium phosphate cement has a relatively high density, eg., a density in the range of from about 15 to about 17 pounds per gallon, which is too high for geothermal applications. That is, in geothermal wells the hydrostatic pressure exerted by the high density calcium phosphate cement often exceeds the fracture gradients of subterranean zones penetrated by the well bore which causes the formation of fractures into which the cement is lost. While calcium phosphate cements have been developed which include hollow microspheres and as a result have densities of about 10 pounds per gallon, such light weight compositions are relatively expensive and the presence of the microspheres in the cured cement reduces its compressive strength.

Thus, there is a need for improved less expensive well cement compositions useful in cementing high temperature wells containing carbon dioxide.

SUMMARY OF THE INVENTION The present invention provides improved cement compositions and methods which meet the needs described above and overcome the deficiencies of the prior art. The compositions are particularly useful in high temperature wells containing carbon dioxide such as geothermal wells. A composition of the present invention is basically comprised of calcium aluminate, fly ash and sufficient water to form a 331387 pumpable slurry.

Another composition of this invention is comprised of calcium aluminate, fly ash, sufficient water to form a pumpable slurry, a foaming agent, a foam stabilizer and a gas sufficient to form a foam having a density in the range of from about 9.5 to about 14 pounds per gallon.

Yet another composition of this invention is comprised of calcium aluminate, sodium polyphosphate, fly ash, sufficient water to form a pumpable slurry, a foaming agent, a foam stabilizer and a gas present in an amount sufficient to form a foam having a density in the range of from about 9.5 to about 14 pounds per gallon.

The methods of the present invention for cementing a high temperature subterranean zone containing carbon dioxide penetrated by a well bore basically comprise the steps of forming a well cement composition of this invention, pumping the cement composition into the subterranean zone by way of the well bore and allowing the cement composition to set into a hard impermeable mass therein.

Described herein are light weight high temperature well cement compositions and methods.

Further described herein are improved carbonation resistant well cement compositions and methods.

It is an object of the present invention to overcome the abovementioned disadvantages or at least to provide the public with a useful choice.

Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in Intellectual property office of n.z. 2 3 OCT 1998 4 331387 the art upon a reading of the description of preferred embodiments which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS As mentioned above, high temperature wells containing carbon dioxide such as geothermal wells generally require the use of well cement compositions which do not deteriorate in the presence of carbon dioxide containing brines. The term "high temperature" is used herein to mean wells wherein the static bottom hole temperature is above about 300°F up to ay high as about 700°F. When conventional hydraulic cements are utilized in such wells, carbonation causes dissolution of the cement which is converted into water-soluble salts. Further, severe corrosion of steel pipe takes place thereby resulting in the total disruption of the conventional cement supported well structure.

When conventional normal density cement slurries are utilized in geothermal and other similar wells, loss of circulation problems are often encountered. This is due to the weak unconsolidated formations in the wells having very low fracture gradients. When a relatively high density cement slurry is pumped into such a well, the hydrostatic pressure exerted on the weak unconsolidated subterranean zones therein causes the zones to fracture. This in turn causes the cement slurry being pumped to enter the fractures and lost circulation problems to occur. To avoid such problems, the cement compositions utilized in geothermal and other similar wells must be of light weight, i.e., have densities in the range of 33138 from about 9.5 to about 14 pounds per gallon.

By the present invention, improved well cement compositions are provided which resist high temperature carbonation deterioration. A cement composition of this invention which can be non-foamed or foamed is basically comprised of calcium aluminate, fly ash and sufficient water to form a pumpable slurry. When foamed, the cement composition includes a foaming agent, a foam stabilizer and a gas present in an amount sufficient to form a foam having a density in the range of from about 9.5 to about 14 pounds per gallon.

Another composition of this invention is comprised of calcium aluminate, sodium polyphosphate, fly ash, a foaming agent, a foam stabilizer and a gas present in an amount sufficient to form a foam having a density in the range of from about 9.5 to about 14 pounds per gallon.

The calcium aluminate can be any commercial grade calcium aluminate suitable for use as a cement. A suitable such calcium aluminate is commercially available from the Lehigh Portland Cement Company of Allentown, Pennsylvania, under the trade designation "REFCON™." The calcium aluminate is generally included in the cement composition in an amount in the range of from about 15% to about 45% by weight of the composition.

When used, the sodium polyphosphate includes sodium hexametaphosphate and sodium triphosphate as well as vitreous sodium phosphates. A suitable sodium polyphosphate for use in accordance with the present invention is commercially available 33138 6 from Calgon Corporation of Pittsburgh, Pennsylvania. The sodium polyphosphate can be included in the cement composition in an amount in the range of from about 5% to about 20% by weight of the composition. When included, the sodium polyphosphate combines with the calcium aluminate to form calcium phosphate in the form of hydroxyapatite.

Fly ash is the finally divided residue that results from the combustion of ground or powdered coal and is carried by the flue gases generated. A particular fly ash that is suitable in accordance with the present invention is a fine particle size ASTM class F fly ash having a Blaine fineness of about 10,585 square centimeters per gram which is commercially available from LaFarge Corporation of Michigan under the trade designation "POZMIX™." Another fly ash that is suitable is an ASTM class F fly ash which is commercially available from Halliburton Energy Services of Dallas, Texas under the trade designation "POZMIX™ A." The fly ash is generally included in the composition in an amount in the range from about 25% to about 45% by weight of the composition.

The major crystalline phase of ASTM class F fly ash is mullite (3A1203* 2Si02) . It reacts with calcium aluminate to form calcium alumino silicate (CaO*A1203* 2Si02> . Also, iron and quartz in the fly ash react with the calcium aluminate to form andradite (Ca3Fe2Si04) 3. These reactions increase the compressive strength of the set cement as compared to set calcium aluminate cement alone.

The water utilized can be from any source provided it does 33138 not contain an excess of compounds that adversely affect other compounds in the cement composition. For example, the water can be fresh water or saltwater. Generally, the water is present in the cement composition in an amount sufficient to form a pumpable slurry, i.e., an amount in the range of from about 10% to about 60% by weight of the composition.

In order to facilitate the foaming of the cement composition, a foaming agent is included in the composition. A particularly suitable and preferred such foaming agent is an alpha-olefinic sulfonate having the formula H (CH2) n-CH=CH- (CH2)mS03Na wherein n and m are individually integers in the range of from about 6 to about 16. The foaming agent is generally included in the cement composition in an amount in the range of from about 1% to about 2% by weight of the water in the composition.

The most preferred foaming agent of this type is an alpha-olefinic sulfonate having the above formula wherein n and m are each 16, i.e., a sulfonic acid Ci6-i6 alkane sodium salt.

A foam stabilizer is also included in the cement composition to enhance the stability of the composition after it is foamed. A particularly suitable and preferred stabilizing agent is an amidopropylbetaine having the formula R-CONHCH2CH2N+ (CH3) 2CH2CO2~ wherein R is a radical selected from the group of decyl, cetyl, oleyl, lauryl and cocoyl. The foam stabilizer is generally included in the cement composition in an amount in the range of from about 0.5% to about 1% by weight of the water in the 33138 composition. The most preferred foam stabilizer of this type is cocoylamidopropylbetaine.

The gas utilized to foam the composition can be air or nitrogen, with nitrogen being the most preferred. The amount of gas present in the cement composition is that amount which is sufficient to form a foam having a density in the range of from about 9.5 to 14 pounds per gallon, most preferably 12 pounds per gallon.

In order to provide resiliency to the set cement composition of this invention, the composition may optionally include inert ground rubber particles. Such particles are produced from worn out tires and are commercially available from Four D Corporation of Duncan, Oklahoma.

At static well bore temperatures above about 125°F, a set retarder is required. The set retarder functions to lengthen the time in which the cement composition starts to thicken and set so that the composition can be pumped into the well bore and into the zone to be cemented before such thickening takes place. Preferred such set retarders for use in accordance with this invention are gluconic acid and citric acid. When used, the set retarder is included in the cement composition in an amount in the range of from about 0.5% to about 2% by weight of the composition.

A preferred composition of the present invention is comprised of calcium aluminate present in an amount of about 30% by weight of the composition, ASTM class F fly ash present in an amount of about 50% by weight of the composition and 331387 water present in an amount sufficient to form a slurry.

Another preferred composition of the present invention is comprised of calcium aluminate present in an amount of about 30% by weight of the composition, ASTM class F Fly Ash present in an amount ox about 50% by weight of the composition, sufficient water to form a pumpable slurry, a foaming agent comprised of a sulfonic acid Ci6-i6 alkane sodium salt present in an amount of about 1.5% by weight of the water in the composition, a foam stabilizer comprising cocoylamidopropylbetaine present in an amount of about 0.75% by weight of the water in the composition and a gas present in an amount sufficient to form a foam having a density in the range of from about 9.5 to about 14 pounds per gallon.

■Y«L another preferred composition of this invention is comprised of calcium aluminate present in an amount of about 28% by weight of the composition, sodium polyphosphate present in an amount of about 19% by weight of the composition, ASTM class F fly ash present in an amount of about 4 9% by weight of the composition, sufficient water to form a pumpable slurry, a foaming agent comprised of a sulfonic acid C16-16 alkane sodium salt present in an amount of about 8% by weight of the water in the composition, a foam stabilizer comprising cocylamideopropylbetaine present in an amount of about 4% by weight of the water in the composition and a gas present in an amount sufficient to form a foam having a density in the range of from about 9.5 to about 14 pounds per gallon.

As previously mentioned, the above described cement 3313 compositions can include ground rubber particles present in an amount in the range of from about 10% to about 4 0% by weight of the compositions to improve the resiliency of the compositions.

Further, when the static well bore temperature is above about 125°F, a set retarder selected from the group of gluconic acid and citric acid is included in the cement compositions in an amount of about 1.0% by weight of the compositions.

The cement compositions of this invention may be prepared in accordance with any of the mixing techniques utilized in the art. In one preferred method, a quantity of water is introduced into a cement blender followed by the sodium polyphosphate (if used), calcium aluminate and fly ash. The mixture is agitated for a sufficient period of time to form a pumpable non-foamed slurry.

When the cement slurry formed as above is foamed, the slurry is pumped to the well bore and the foaming agent and foam stabilizer followed by the gas utilized are injected into the slurry on the fly. As the slurry and gas flow through the well bore to the location where the resulting foamed cement composition is to be placed, the cement composition is foamed and stabilized. Other liquid additives utilized, if any, are added to the water prior to when the other components of the cement composition are mixed therewith and other dry solids, if any, are added to the water and cement prior to mixing.

The methods of this invention of cementing a high temperature subterranean zone containing carbon dioxide penetrated by a well bore are basically comprised of the steps 33138 of forming a foamed cement composition of this invention, pumping the foamed cement composition into the subterranean zone to be cemented by way of the well bore and then allowing the foamed cement composition to set into a hard impermeable mass therein.

In order to further illustrate the improved cement compositions and methods of this invention, the following examples are given.

Example 1 In a controlled test, API Class G Portland Cement was mixed with 4 0% silica flour and water to form a cement slurry.

The slurry was allowed to set for 24 hours at a temperature of 190°F. Thereafter, the set cement was placed in an aqueous 4% by weight sodium carbonate solution for 28 days at 600°F.

A calcium phosphate cement composition was prepared comprised of 23.3% water; 17.5% calcium aluminate; 15.6% sodium polyphosphate; 40.8% ASTM class F fly ash, 1.9% sulfonic acid Ci6-i6 alkane sodium salt foaming agent and 0.9% cocoylamidopropylbetaine foam stabilizer, all by weight of the composition. After mixing, the resulting slurry was allowed to set for 24 hours at a temperature of 190°F. Thereafter, the set cement was placed in a 4% by weight aqueous sodium carbonate solution for 2 8 days at 600°F.

At the end of the test periods, samples from the interiors of the set Portland Cement composition and calcium aluminate cement composition were tested. The tests showed that the Portland Cement composition contained 1.5% by weight calcium 33 j 38 7 ## 6 12 carbonate and the calcium phosphate cement contained none. Samples were also tested taken from the exteriors of the set cements which showed that the Portland cement composition contained 10.6% calcium carbonate while the calcium phosphate cement contained none.

Example 2 Test calcium phosphate cement slurry samples were prepared by mixing 240 grams of water with 180 grams of calcium aluminate, 160 grams of sodium polyphosphate and 420 grams of fly ash for each sample. Various Portland cement set retarding additives were combined with the test samples. After mixing, each test sample was tested for thickening time at 125°F in accordance with the test procedure set forth in API Specification For Materials And Testing For Well Cements, API Specification 10, 5th ed., dated July 1, 1990 of the American Petroleum Institute. The set retarders tested are identified and the thickening time test results are set forth in Table 1 below.

TABLE I Thickening Time Tests' Set Retarder Tested Amount Added to Test Sample, grams Thickening Time, hrs.:mins.

None — 1:35 Acrylic Acid Polymer 6 2:02 Tartaric Acid 6 1:12 Gluconic Acid 6 4:05 Citric Acid 6 6:00+ 1 API Tests at 125°F. 33138 13 From Table I, it can be seen that gluconic acid and citric acid are the most effective set retarders for the calcium aluminate cement composition at a temperature of 125°F.

Example 3 Two additional calcium aluminate cement slurry samples were prepared as shown in Table II below. After mixing, the resulting slurries were allowed to set for 24 hours at 190°F. Thereafter, the set samples were placed in 4% by weight aqueous sodium carbonate solutions for 28 days at 600°F. At the end of the 28 day periods, the samples were tested for compressive strengths in accordance with the above mentioned API Specification 10. The results of the tests are also set forth in Table II below.

TABLED Compressive Strength Tests Sample Sample Components, grams Density Compressive No. Calcium Sodium Fly Foaming Foam lb/gal. Strength, Water Aluminate' Phosphate2 Ash3 Agent4 Stabilized psi 1 465.5 350 311.5 815.5 37.3 18.6 12.1 570 2 266 200 178 466 21.3 10.6 15.1 1060 1 "REFCON™" from Lehigh Portland Cement Co. 2 Calgon Sodium Polyphosphate 3 ASTM class F fly ash from LaFarge Corp. 4 Sulfonic acid CIS.,6 alkane sodium salt Cocoylamidopropylbetaine From Table II, it can be seen that the calcium aluminate cement compositions of the present invention maintained their compressive strengths after 28 days in the presence of sodium 3313? carbonate solutions at 600°F.

Example 4 An API Class G Portland cement was mixed with 40% silica flour and water to form a cement slurry. The slurry was allowed to set for hours at a temperature of 500°F.

Thereafter, the set cement was placed in an aqueous solution containing 2.4% dry ice and 0.8% sulfuric acid. A calcium aluminate cement composition was prepared comprised of 30% water, 37% calcium aluminate and 33% ASTM class F fly ash. The resulting slurry was allowed to set for 4 8 hours at a temperature of 500°F. Thereafter, the set cement was placed in an aqueous solution containing 2.4% dry ice and 0.8% sulfuric acid. The above described test cement samples were kept in the carbonate-acid solutions for 53 days at 500°F, after which the Portland cement lost 33% of its weight while the calcium aluminate cement gained 9.1% in weight.

Calcium aluminate (Lehigh "REFCON™") was mixed with 59% by weight water and cured for 24 hours at 500°F. The same calcium aluminate was mixed with ASTM class F fly ash in an amount of 75% by weight of the calcium aluminate and with water in an amount of 34% by weight of calcium aluminate and cured for 24 hours at 500°F. The set samples were tested for compressive strengths in accordance with the above mentioned API Specification 10. The set sample formed with calcium aluminate alone had a compressive strength of only 410 psi while the sample formed with calcium aluminate and fly ash had a

Claims (44)

3313 15 compressive strength of 2120 psi. Thus, the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned as well as those which are inherent therein. While numerous changes may be made by those skilled in the art, such changes are encompassed within the spirit of this invention as defined by the appended claims. WHAT XFNE CLAIM IS 16

1. A cement composition useful in cementing high temperature wells containing carbon dioxide consisting essentially of: calcium aluminate present in an amount in the range of from about 15% to about 45% by weight of said composition; fly ash present in an amount in the range of from about 25% to about 45% by weight of said composition; and sufficient water to form a pumpable slurry.

2. The composition of claim 1 wherein said water is selected from the group of fresh water and saltwater.

3. The composition of claim 1 wherein said water is present in said composition in an amount in the range of from about 10% to about 60% by weight of said composition.

4. The composition of claim 1 which further comprises ground rubber particles present in an amount in the range of from about 10% to about 40% by weight of said composition.

5. The composition of claim 1 which further comprises an effective amount of a set retarder selected from the group of gluconic acid and citric acid.

6. The composition of claim 1 which further comprises an effective amount of a foaming agent, an effective amount of a foam stabilizer and a gas present in an amount sufficient to form a foam having a density in the range of from about 11.5 to about 15 pounds per gallon.

7. The composition of claim 6 wherein said foaming agent comprises an alpha-olefinic sulfonate having the formula H (CH2) n-CH=CH- (CH2)mS03Na 33138 7 INTELLECTUAL PflOPffiTY OFFICE 0F-^2. 331387 wherein n and m are individually integers in the range of from about 6 to about 16 present in an amount in the range of from about 1.0% to about 2.0% by weight of water in said composition and said foam stabilizer comprises a betaine having the formula R-CONHCH2CH2N+ (CH3) 2CH2CO2" wherein R is a radical selected from the group of decyl, cetyl, oleyl, lauryl and cocoyl present in an amount in the range of from about 0.5% to about 1.0% by weight of water in said composition.

8. The composition of claim 7 wherein said alpha-olefinic sulfonate is sulfonic acid Ci6-i6 alkane sodium salt.

9. The composition of claim 7 wherein said betaine is cocoylamidopropylbetaine.

10. A cement composition useful in cementing high temperature wells containing carbon dioxide comprising: calcium aluminate present in an amount in the range of from about 15% to about 45% by weight of said composition; fly ash present in an amount in the range of from about 25% to about 4 5% by weight of said composition; sufficient water to form a pumpable slurry; a foaming agent present in an amount effective to facilitate foaming; a foam stabilizer present in an amount effective to stabilize a foam; and a gas present in an amount sufficient to form a foam having a density in the range of from about 9.5 to about 14 pounds per gallon.

11. The composition of claim 10 wherein said water is selected from the group of fresh water and salt water. intellectual PROPERTY OFFICE OF N.Z. 2 3 OCT 1998 RECEWED 33138 18 ... '

12. The composition of claim 10 wherein said water is present in said composition in an amount in the range of from about 20% to about 50% by weight of said composition.

13. The composition of claim 10 which further comprises ground rubber particles present in an amount in the range of from about 10% to about 40% by weight of said composition.

14. The composition of claim 10 which further comprises an effective amount of a set retarder selected from the group of gluconic acid and citric acid.

15. The composition of claim 10 wherein said foaming agent comprises an alpha-olefinic sulfonate having the formula H (CH2) n-CH=CH- (CH2) mS03Na wherein n and m are individually integers in the range of from about 6 to about 16 present in an amount in the range of from about 1.0% to about 2.0% by weight of water in said composition.

16. The composition of claim 10 wherein said foam stabilizer comprises a betaine having the formula R-CONHCH2CH2N+ (CH3) 2CH2CO2" wherein R is a radical selected from the group of decyl, cetyl, oleyl, lauryl and cocoyl present in an amount in the range of from about 0.5% to about 1.0% by weight of water in said composition.

17. The composition of claim 10 wherein said gas is selected from the group of nitrogen and air.

18. A light weight well cement composition useful in cementing high temperature wells containing carbon dioxide 33138 19 comprising: calcium aluminate present in an amount of about 28% by weight of said composition; sodium polyphosphate present in an amount of about 19% by weight of said composition; ASTM class F fly ash present in an amount of about 4 9% by weight of said composition; sufficient water to form a pumpable slurry; a foaming agent present in an amount effective to facilitate foaming; a foam stabilizer present in an amount effective to stabilize a foam; and a gas present in an amount sufficient to form a foam having a density in the range of from about 9.5 to about 14 pounds per gallon.

19. The composition of claim 18 wherein said foaming agent is a sulfonic acid Ci6-i6 alkane sodium salt and is present in an amount of about 2% by weight of said composition.

20. The composition of claim 18 wherein said foam stabilizer is cocoylamidopropylbetaine and is present in an amount of about 1% by weight of said composition.

21. The composition of claim 18 which further comprises ground rubber particles present in an amount in the range of from about 10% to about 40% by weight of said composition.

22. The composition of claim 18 which further comprises an effective amount of a set retarder selected from the group of gluconic acid and citric acid. 331337 20

23. A method of cementing a subterranean zone containing carbon dioxide penetrated by a well bore comprises the steps of: (a) forming a well cement composition comprised of calcium aluminate, fly ash and sufficient water to form a pumpable slurry; (b) pumping said cement composition into said subterranean zone by way of said well bore; and (c) allowing said cement composition to set into a hard impermeable mass therein.

24. The method of claim 23 wherein said water is selected from the group of fresh water and salt water.

25. The method of claim 23 wherein said calcium aluminate is present in said composition in an amount in the range of from about 15% to about 45% by weight of said composition.

26. The method of claim 23 wherein said fly ash is present in said composition in an amount in the range of from about 25% to about 45% by weight of said composition.

27. The method of claim 23 which further comprises an effective amount of a foaming agent, an effective amount of a foam stabilizer and a gas present in an amount sufficient to form a foam having a density in the range of from about 9.5 to about 14 pounds per gallon.

28. The method of claim 27 wherein said foaming agent comprises an alpha-olefinic sulfonate having the formula H (CH2) n-CH=CH- (CH2) mS03Na wherein n and m are individually integers in the range of from 3313 € 21 about 6 to about 16 present in an amount in the range of from about 1.0% to about 2.0% by weight of water in said composition and said foam stabilizer comprises a betaine having the formula R-CONHCH2CH2N+ (CH3) 2CH2CO2" wherein R is a radical selected from the group of decyl, cetyl, oleyl, lauryl and cocoyl present in an amount in the range of from about 0.5% to about 1.0% by weight of water in said composition.

29. The method of claim 27 wherein said alpha-olefinic sulfonate is sulfonic acid Ci6-i6 alkane sodium salt.

30. The method of claim 27 wherein said betaine is cocoylamidopropylbetaine.

31. A method of cementing a high temperature subterranean zone containing carbon dioxide penetrated by a well bore comprising the steps of: (a) forming a light weight well cement composition comprised of calcium aluminate, sodium polyphosphate, fly ash, sufficient water to form a pumpable slurry, a foaming agent, a foam stabilizer and a gas present in an amount sufficient to form a foam having a density in the range from about 9.5 to about 14.0 pounds per gallon; (b) pumping said cement composition into said subterranean zone by way of said well bore; and (c) allowing said cement composition to set into a hard impermeable mass therein.

32. The method of claim 31 wherein said water is selected from the group of fresh water and saltwater. 33138 7

33. The method of claim 31 wherein said foaming agent is an alpha-olefinic sulfonate.

34. The method of claim 33 wherein said alpha-olefinic sulfonate is a sulfonic acid Ci6-i6 alkane sodium salt and is present in said composition in an amount in the range of from about 1% to about 2% by weight of water in said composition.

35. The method of claim 31 wherein said foam stabilizer is a betaine.

36. The method of claim 35 wherein said betaine is cocoylamidopropylbetaine and is present in said composition in an amount in the range of from about 0.5% to about 1% by weight of water in said composition.

37. The method of claim 31 wherein said calcium aluminate is present in said composition in an amount in the range of from about 15% to about 45% by weight of said composition.

38. The method of claim 31 wherein said sodium polyphosphate is present in said composition in an amount in the range of from about 5% to about 20% by weight of said composition.

39. The method of claim 31 wherein said fly ash is present in said composition in an amount in the range of from about 25% to about 45% by weight of said composition.

40. The method of claim 31 wherein said composition further comprises ground rubber particles present in an amount in the range of from about 10% to about 40% by weight of said composition. 331387 23

41. A cement composition useful in cementing high temperature wells containing carbon dioxide as claimed in claim 1 or 10 substantially as herein described with reference to any example thereof.

42. A light weight well cement composition useful in cementing high temperature wells containing carbon dioxide as claimed in claim 18 substantially as herein described with reference to any example thereof.

43. A method of cementing a subterranean zone containing carbon dioxide penetrated by a well bore as claimed in claim 23 substantially as herein described with reference to any example thereof.

44. A method of cementing a high temperature subterranean zone containing carbon dioxide penetrated by a well bore as claimed in claim 31 substantially as herein described with reference to any example thereof. END OF CLAIMS intellectual PROPERTY OFFICE OF N.Z. 2 3 OCT 1998 RECEIVED