Wells – Processes – Cementing – plugging or consolidating
Reexamination Certificate
2003-05-16
2004-01-27
Bagnell, David (Department: 3672)
Wells
Processes
Cementing, plugging or consolidating
C166S292000
Reexamination Certificate
active
06681856
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improved methods of cementing subterranean zones penetrated by well bores using biodegradable dispersants.
2. Description of the Prior Art
Subterranean zones penetrated by well bores are commonly sealed by hydraulic cement compositions. For example, hydraulic cement compositions are used in primary cementing operations whereby strings of pipes such as casing and liners are cemented in well bores. In performing primary cementing, a hydraulic 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 which supports and positions the pipe string in the well bore and seals the exterior surfaces of the pipe string to the walls of the well bore. Hydraulic cement compositions are also utilized in a variety of cementing operations such as sealing highly permeable zones or fractures in subterranean zones, plugging cracks or holes in pipe strings and the like.
Dispersing agents are commonly included in hydraulic cement compositions used for cementing subterranean zones. The dispersing agents reduce the rheologies of the cement compositions, i.e., the apparent viscosities and other properties of the cement compositions, as well as reducing the water content of the cement compositions. The reduction of the rheology of a cement composition allows the cement composition to be pumped with less friction pressure and less pump horse power. In addition, the lower rheology often allows the cement composition to be pumped in turbulent flow. Turbulent flow characteristics are desirable when pumping cement compositions in wells in that drilling fluid is more efficiently removed from surfaces in the well bore as the drilling fluid is displaced by the cement compositions being pumped. The inclusion of dispersing agents in cement compositions is also desirable in that the presence of the dispersing agents reduces the water required for preparation of the cement compositions. Cement compositions having reduced water content set into cement masses having improved compressive strengths.
A number of dispersing agents have been utilized heretofore in cement compositions, particularly in cement compositions used for primary and remedial cementing in oil and gas wells. However, most of such dispersing agents are also strong cement composition set retarding agents which is often undesirable. That is, the presence of such a dispersant in a cement composition prevents the cement composition from setting for a relatively long period of time which is often costly or otherwise detrimental. While various other cement dispersants have been developed and used which do not substantially increase the setting time of cement compositions, they are not environmentally acceptable, especially in offshore operations in that they do not undergo complete biodegradation in the environment and cause damage to aquatic and other life therein. Thus, there are continuing needs for improved biodegradable cement composition dispersants and improved cement compositions containing such dispersants.
SUMMARY OF THE INVENTION
The present invention provides improved methods and compositions for cementing subterranean zones penetrated by well bores which meet the needs described above and overcome the deficiencies of the prior art. The methods of the invention for cementing subterranean zones penetrated by well bores basically comprise the following steps. A cement composition that comprises a hydraulic cement, sufficient water to form a slurry and a water soluble biodegradable cement dispersant comprising a polyamide graft copolymer containing at least one side chain formed from aldehydes and sulfur-containing acids or their salts is prepared or provided. The cement composition is placed in the subterranean zone to be cemented, and then the cement composition is allowed to set into a solid mass therein.
A well cement composition of this invention basically comprises a hydraulic cement, sufficient water to form a slurry and a water soluble biodegradable cement dispersant comprising a polyamide graft copolymer containing at least one side chain formed from aldehyde and sulfur-containing acids or their salts.
The 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 methods of cementing a subterranean zone penetrated by a well bore in accordance with the present invention comprise the following steps. A cement composition is prepared or provided that comprises a hydraulic cement, sufficient water to form a slurry and a water soluble biodegradable cement dispersant. The cement composition is placed in a subterranean zone to be cemented and the cement composition is then allowed to set into a solid mass therein.
The cement compositions of this invention basically comprise a hydraulic cement, sufficient water to form a slurry, and a water soluble biodegradable cement dispersant comprising a polyamide graft copolymer containing at least one side chain formed from aldehydes and sulfur-containing acids or their salts.
The polyamide component of the graft copolymer is a natural polyamide. Examples of such natural polyamides which can be utilized include, but are not limited to, casein, gelatin, soy protein, polyaspartic acid, collagens, bone binders, blood albumins, and their degradation products. Of these, gelatin is generally preferred. The polyamide component is generally present in the graft copolymer in an amount in the range of from about 5% to about 80% by weight, more preferably in an amount of from about 10% to about 60% by weight.
Examples of the aldehyde component of the graft copolymer include, but are not limited to, paraformaldehyde, paraldehyde, formaldehyde, acetaldehyde, and glyoxal. Of these, formaldehyde is generally preferred. The aldehyde component of the graft copolymer is generally present therein in an amount in the range of from about 5% to about 90% by weight, more preferably in an amount from about 10% to about 70% by weight.
Examples of the sulfur-containing acid or salt thereof component of the graft copolymer include, but are not limited to, inorganic sulfite salts, hydrogen sulfite, bisulfites of alkaline earth metals, aluminum, iron and ammonium, napthalenesulfonic acid and its salts, and benzenesulfonic acid and its salts. Of these, inorganic sulfite salts are preferred with sodium sulfite being the most preferred. The sulfur-containing acid or salt component of the graft copolymer is present therein in an amount in the range of from about 5% to about 60% by weight, more preferably in an amount from about 15% to about 40% by weight.
The side chain formed from aldehydes and sulfur-containing acids or their salts can also include at least one additional compound selected from the group consisting of ketones, aromatic alcohols and aminoplastic-forming agents such as dicyanodiamide, urea derivatives, aminio-s-triazines, melamines, and melamine derivatives. Of these, ketones are preferred such as acetone, 2-propanone, 2-butanone, and pyruvic acid. Of these, acetone is the most preferred. When included, the additional compound in the side chain is present in the graft copolymer in an amount in the range of from about 5% to about 85% by weight, more preferably in an amount of from about 10% to about 70% by weight.
The biodegradable cement dispersant is prepared by graft polymerization at temperatures between −10° C. and 250° C. The polymerization is conducted in the presence of a solvent such as water or dimethyl sulfoxide. Alternatively, the dispersant can be prepared by thermal treatment.
A particularly preferred biodegradable cement graft copolymer dispersant comprises gelatin present in an amount of about 42% by weight, a 37%
Brenneis D. Chad
Chatterji Jiten
Cromwell Roger S.
Bagnell David
Dougherty Jennifer R
Dougherty, Jr. C. Clark
Halliburton Energy Service,s Inc.
Roddy Craig W.
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