Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2000-08-09
2001-12-25
Marcheschi, Michael (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S696000, C106S705000, C106S708000, C106S810000, C106S819000, C106S823000, C106SDIG002, C106S217200, C106S217200
Reexamination Certificate
active
06332921
ABSTRACT:
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 reaction between calcium aluminate and a phosphate-containing 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 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.
It is, therefore, a general object of the present invention to provide light weight high temperature well cement compositions and methods.
A further object of the present invention is the provision of improved carbonation resistant well cement compositions and methods.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in 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 as 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 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, Pa., 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 from Calgon Corporation of Pittsburgh, Pa. 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.
Brenneis D. Chad
Brothers Lance E.
Childs Jerry D.
Ekstrand Barry B.
Turkett Susan M.
Dougherty, Jr. C. Clark
Halliburton Energy Service,s Inc.
Marcheschi Michael
Roddy Craig W.
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