Hydraulic and earth engineering – Earth treatment or control – Chemical
Reexamination Certificate
2003-06-13
2004-05-25
Green, Anthony J. (Department: 1755)
Hydraulic and earth engineering
Earth treatment or control
Chemical
C106S694000, C106S696000, C106S706000, C106S708000, C106S719000, C106S724000, C106S727000, C106S773000, C106S778000, C106S781000, C106S802000, C106S803000, C106S808000, C106S810000, C106S823000, C166S293000, C166S295000, C405S266000, C507S204000, C507S219000, C507S239000, C507S266000, C524S004000, C524S005000, C524S404000
Reexamination Certificate
active
06739806
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to subterranean cementing operations, and more particularly, to fluid loss control additives for cement compositions, and methods of using cement compositions comprising such fluid loss control additives in subterranean formations.
2. Description of the Prior Art
Hydraulic cement compositions are commonly utilized in subterranean operations, particularly subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipe strings such as casings and liners are cemented in well bores. In performing primary cementing, hydraulic cement compositions are pumped into the annular space between the walls of a well bore and the exterior surface of the 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 that substantially 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. Hydraulic cement compositions also are used in remedial cementing operations such as plugging highly permeable zones or fractures in well bores, plugging cracks and holes in pipe strings, and the like.
In order for such well cementing operations to be successful, the cement compositions utilized may include a fluid loss control additive to reduce the loss of fluid, e.g., water, from the cement compositions when they contact permeable subterranean formations and zones. Excessive fluid loss, inter alia, causes a cement composition to be prematurely dehydrated, which may limit the amount of cement composition that can be pumped, decrease the compressive strength of the cement composition and negatively impact bond strength between the set cement composition and a subterranean zone, the walls of pipe and/or the walls of the well bore.
Contemporary synthetic fluid loss control additives are large, water-soluble polymers. An example of such synthetic fluid loss control additive is a fluid loss control additive consisting of copolymers of acrylamide (“AA”) and 2-acrylamido, 2-methyl propane sulfonic acid (“AMPS®”). However, certain AA/AMPS® copolymers are useful only in a limited number of operations, specifically those where the bottom hole circulating temperature (“BHCT”) ranges from about 90° F. to about 125° F. The BHCT ranges encountered in subterranean operations often involve temperatures outside such a range. Also, certain of these copolymers have a salt tolerance of only up to about 10%, making certain of them unsuitable for applications involving cement compositions comprising salts.
The temperature limitations of certain AA/AMPS® copolymers are believed to be the result of hydrolysis of the amide groups. The carboxylate groups formed by such hydrolysis convert the copolymers to materials which retard the set time of the cement and reduce the compressive strength of the set cement. Further, in the lower portion of the above-mentioned temperature range (between about 90° F. to about 100° F.), certain AA/AMPS® copolymers are even less effective as a fluid loss control additive, requiring inclusion of larger amounts of such additive than at higher temperatures. The addition of such copolymers directly affects the rheology of the resultant cement composition, as copolymers of acrylamide and AMPS® exhibit high viscosity and poor mixability, thus the inclusion of a sufficiently large amount of fluid loss control additive to create a cement composition having an acceptable fluid loss often leads to viscosity and pumpability problems.
Additionally, synthetic polymers may not comply with environmental regulations in certain regions of the world. For example, the use of polyamide polymers in the North Sea is problematic. One possible cause of this difficulty is the high molecular weight of such synthetic polymers.
SUMMARY OF THE INVENTION
The present invention provides cement compositions which demonstrate improved fluid loss characteristics, and methods for cementing in a subterranean formation using such cement compositions.
One method of the present invention comprises the steps of providing a cement composition comprising a hydraulic cement, water, and a fluid loss control additive comprising at least two polymers connected by a pH-sensitive crosslink; placing the cement composition into the subterranean formation; and permitting the cement composition to set therein.
One embodiment of the cement compositions of the present invention comprises a hydraulic cement, water, and a fluid loss control additive comprising at least two polymers connected by a pH-sensitive crosslink. Optionally, other additives suitable for inclusion in cement compositions may be added.
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 the preferred embodiments, which follows.
DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention provides cement compositions that have improved fluid loss characteristics and methods of using such cement compositions in subterranean formations. While the compositions and methods of the present invention are useful in a variety of subterranean applications, they arc particularly useful for subterranean well completion and remedial operations, such as primary cementing, e.g., cementing casings and liners in well bores, including those in production wells, which include multi-lateral subterranean wells.
The cement compositions of the present invention generally comprise a hydraulic cement, water sufficient to form a pumpable slurry, and a fluid loss control additive of the present invention. The cement compositions of the present invention may range in density from about 4 lb/gallon to about 23 lb/gallon. In certain preferred embodiments, the density of the cement compositions may range from about 12 lb/gallon to about 17 lb/gallon. In certain other embodiments, the cement compositions can be low-density cement compositions, e.g., foamed cement compositions or cement compositions comprising other means to reduce their densities, e.g., microspheres.
Any cements suitable for use in subterranean applications are suitable for use in the present invention. In certain preferred embodiments, the improved cement compositions of the present invention comprise a hydraulic cement. A variety of hydraulic cements are suitable for use including those comprised of calcium, aluminum, silicon, oxygen, and/or sulfur, which set and harden by reaction with water. Such hydraulic cements include, but are not limited to, Portland cements, pozzolanic cements, gypsum cements, high alumina content cements, silica cements, and high alkalinity cements. In certain preferred embodiments, the hydraulic cement is a Portland cement.
The cement compositions of the present invention further comprise water, which can be from any source provided that it does not contain an excess of compounds that adversely affect other compounds in the cement compositions. For example, a cement composition of the present invention can comprise fresh water, salt water (e.g., water containing one or more salts dissolved therein), brine (e.g., saturated salt water), or seawater. The water may be present in an amount sufficient to form a pumpable slurry. More particularly, the water is present in the cement compositions of the present invention in an amount in the range of from about 16% to about 220% by weight of cement (“bwoc”) therein. In certain preferred embodiments, the water is present in the cement compositions in the range of from about 30% to about 70% bwoc therein.
The cement compositions of the present invention also comprise a fluid loss control additive of the present invention, present in the cement composition in an amount sufficient to provide a desired level of fluid loss control. More particularly, the fluid loss control additive may be present in the cement compositions of t
Eoff Larry S.
Lewis Samuel J.
Szymanski Michael J.
Wilson John Michael
Baker & Botts L.L.P.
Green Anthony J.
Halliburton Energy Service,s Inc.
Roddy Craig W.
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