Wells – Processes – Cementing – plugging or consolidating
Reexamination Certificate
2000-05-12
2001-05-08
Suchfield, George (Department: 3672)
Wells
Processes
Cementing, plugging or consolidating
C166S309000, C106S677000, C106S678000, C106S725000, C106S727000, C106S819000, C106S820000, C106S823000
Reexamination Certificate
active
06227294
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improved methods of cementing in subterranean zones with set retarded foamed cement compositions.
2. Description of the Prior Art
Foamed hydraulic cement compositions are often utilized in cementing subterranean zones penetrated by well bores. For example, foamed cement compositions are used in primary well cementing operations whereby strings of pipe such as casing and liners are cemented in well bores. In performing primary cementing, a cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a pipe string disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe string in the well bore and bonds the exterior surfaces of the pipe string to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented.
The cement compositions utilized for cementing in subterranean zones or formations penetrated by well bores must often be lightweight to prevent excessive hydrostatic pressure from unintentionally fracturing the zones or formations. In addition to being lightweight, a foamed cement composition contains compressed gas which improves the ability of the cement composition to maintain pressure and prevent the flow of formation fluid into and through the cement composition during the transition time, i.e., the time during which the cement composition changes from a true fluid to a hard set mass. Foamed cement compositions are also advantageous because they have low fluid loss properties.
When cement compositions are utilized for cementing in deep hot subterranean zones, a set retarder must be included in the cement composition to increase the pumping time of the composition and prevent premature thickening or setting before placement in the zones to be cemented. Examples of set retarders which have heretofore been utilized in non-foamed cement compositions include, but are not limited to, lignosulfonates, sulfomethylated lignosulfonates, hydroxycarboxy acids, mixtures of sulfomethylated lignosulfonates and hydroxycarboxy acids, acrylic acid/2-acrylamido-2-methyl propane sulfonic acid copolymers and the like. While the foregoing set retarders function well in non-foamed cement compositions, they do not function well in foamed cement compositions because they have dispersing properties. That is, when used in a foamed cement composition, a set retarder having dispersing properties causes the cement slurry to be thin which in turn causes the foam to be unstable and either break or significantly decrease the viscosity of the foamed cement slurry which in turn prevents the desired foamed cement composition low density from being achieved. While carboxymethylhydroxyethylcellulose (CMHEC) has heretofore been used in foamed cement compositions as a set retarder, the high concentrations of CMHEC required for high temperatures causes the foamed compositions to have undesirable high surface viscosities.
Thus, there are needs for improved methods and set retarded foamed cement compositions for cementing subterranean zones penetrated by well bores.
SUMMARY OF THE INVENTION
The present invention provides improved methods and set retarded foamed cement compositions for cementing in subterranean zones penetrated by well bores which meet the needs described above and overcome the deficiencies of the prior art. The improved methods of this invention are basically comprised of the following steps. A foamed cement composition is prepared comprised of hydraulic cement, a non-dispersing set retarder comprised of a mixture of a lignosulfonate, sugar acids and a sulfonated lignin, sufficient water to form a slurry, sufficient gas to foam the slurry and a foaming and foam stabilizing surfactant mixture. The foamed cement composition is then placed into a subterranean zone, and the foamed cement composition is allowed to set into a solid mass therein.
It is, therefore, a general object of the present invention to provide improved methods of cementing in subterranean zones penetrated by well bores.
A further object of the present invention is to provide improved methods of cementing in subterranean zones penetrated by well bores with a foamed cement slurry containing a non-dispersing set retarder.
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
The improved methods and foamed cement compositions of the present invention are particularly suitable for performing a variety of completion and remedial procedures in subterranean zones or formations penetrated by well bores. The foamed cement compositions have improved properties in that they include a non-dispersing set retarder which does not cause the foamed cement compositions to break or decrease in viscosity whereby the density of the foamed cement compositions increases. Since it is often very important that the density of a foamed cement composition be as low as possible, an increase in density can cause adverse cementing results, e.g., fracturing of the formation or zone being cemented.
The foamed cement compositions useful in accordance with this invention are basically comprised of a hydraulic cement, a non-dispersing set retarder comprised of a mixture of a lignosulfonate, one or more sugar acids and a sulfonated lignin, sufficient water to form a slurry, sufficient gas to foam the slurry and a foaming and foam stabilizing surfactant mixture present in an amount sufficient to facilitate the formation of the foam and stabilize the foamed cement composition.
U.S. patent application Ser. No. 09/569,422, filed May 12, 2000 entitled Set Retarders For Foamed Cements filed of even date herewith which describes and claims similar non-dispersing set retarders and foamed cement compositions is incorporated herein in its entirety by reference.
A variety of hydraulic cements can be utilized in accordance with the present invention including those comprised of calcium, aluminum, silicon, oxygen and/or sulfur which set and harden by reaction with water. Such hydraulic cements include Portland cements, pozzolana cements, gypsum cements, high alumina content cements, silica cements and high alkalinity cements. Portland cements or their equivalents are generally preferred for use in accordance with the present invention when performing cementing operations in subterranean zones penetrated by well bores. Portland cements of the types defined and described in
API Specification For Materials And Testing For Well Cements
, API Specification 10, 5
th
Edition, dated Jul. 1, 1990 of the American Petroleum Institute are particularly suitable. Preferred API Portland cements include classes A, B, C, G and H, with API classes G and H being more preferred, and class G being the most preferred.
The non-dispersing set retarder utilized in accordance with this invention is a mixture of a lignosulfonate, one or more sugar acids and a sulfonated lignin. The lignosulfonate is a metallic sulfonate salt made from the lignin of sulfite pulp-mill liquors. The specific lignosulfonate which is preferred for use in accordance with this invention is a hardwood lignosulfonate having a sulfur content of about 6% by weight and an average molecular weight of about 9,700 daltons. The one or more sugar acids in the mixture are preferably derived from xylose. The sulfonated lignin in the mixture is preferably a sulfonated kraft lignin, i.e., a lignin produced in the kraft process. The sulfonated kraft lignin preferably has an organic sulfur content of about 3.8% by weight and an average molecular weight of about 60,000 daltons. The non-dispersing set retarder is preferably comprised of a mixture of about 59 parts by weight li
Brenneis Darrell C.
Chatterji Jiten
Cromwell Roger S.
Gray Dennis W.
King Bobby J.
Dougherty, Jr. C. Clark
Halliburton Energy Service,s Inc.
Roddy Craig W.
Suchfield George
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