Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-01-07
2001-07-31
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C166S293000, C166S250140, C524S005000
Reexamination Certificate
active
06268406
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods of cementing subterranean zones penetrated by well bores using cement compositions containing liquid polymeric fluid loss additives.
2. Description of the Prior Art
Hydraulic cement compositions are commonly utilized in the construction and repair of oil and gas wells. For example, hydraulic cement compositions are used in primary cementing operations whereby strings of pipe such as casing or 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. 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. Hydraulic cement compositions are also commonly used to plug lost circulation and other undesirable fluid inflow and outflow zones in wells, to plug cracks and holes in pipe strings cemented therein and to accomplish other required remedial well operations.
In order for such well cementing operations to be successful, the cement compositions utilized must include a fluid loss control additive to reduce the loss of fluid, i.e., water, from the cement compositions when they contact permeable subterranean formations and zones. Excessive fluid loss causes a cement composition to be prematurely dehydrated which limits the amount of cement composition that can be pumped, decreases the compressive strength of the cement composition and prevents or reduces bond strength between the set cement composition and a subterranean zone, the walls of pipe and/or the walls of the well bore.
Heretofore, polymers and copolymers have been utilized as fluid loss control additives for well cements. Particularly suitable copolymers which have been utilized as cement composition fluid loss additives are described in U.S. Pat. No. 4,515,635 issued to Rao et al. on May 7, 1985 and related U.S. Pat. No. 4,555,269 also issued to Rao et al. on Nov. 26, 1985. The foregoing patents disclose certain copolymers of N,N-dimethylacrylamide (NNDMA) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS®) having mole ratios of NNDMA to AMPS® of between 1:4 and 4:1, respectively, and having average molecular weights of between about 75,000 and 300,000. The copolymers or copolymer salts are produced by solution polymerization techniques whereby aqueous polymer solutions containing 10% by weight of NNDMA/AMPS® copolymers or copolymer salts are obtained. However, because the viscosities of the 10% solutions are very high and the solutions are unpourable, the copolymers or copolymer salts were initially utilized as cement composition fluid loss control additives in dried solid form.
In wells drilled offshore, liquid cement composition additives are preferred so that the additives can be premixed with the cement composition mixing water. In order to utilize the above described solid copolymers and copolymer salts in offshore applications, suspensions of the solid copolymers in oil have been developed and used. That is, solid particles of the copolymers or copolymer salts are suspended in mineral oil containing a suspending agent. However, a problem often encountered in the use of the mineral oil suspensions of the copolymers or copolymer salts is that when they are stored, the solids settle and form an unpourable sludge.
Thus, there are needs for improved liquid fluid loss control additives comprised of NNDMA/AMPS® copolymers or copolymer salts which can be stored for long periods of time without settling and becoming unpourable, and for methods of cementing subterranean zones using cement compositions containing such improved liquid fluid loss control additives.
SUMMARY OF THE INVENTION
The present invention provides liquid fluid loss control additives for cement compositions comprised of NNDMA/AMPS® copolymers or copolymer salts which are storable for long periods of time without becoming unpourable and improved methods of cementing subterranean zones penetrated by well bores utilizing cement compositions containing such liquid fluid loss control additives. Thus, the liquid fluid loss control additives and methods of cementing wells of this invention overcome the deficiencies of the prior art and meet the needs described above.
The methods of the invention are basically comprised of the following steps. A cement composition is first prepared comprised of a hydraulic cement, sufficient water to form a slurry and an effective amount of a liquid fluid loss control additive comprised of an emulsion having a copolymer of NNDMA and AMPS® or a salt thereof contained therein. After being prepared, the cement composition is placed in a subterranean zone to be cemented and allowed to set into a hard impermeable mass therein.
The liquid fluid loss control additives useful in accordance with this invention are water-in-oil emulsions having NNDMA/AMPS® copolymers or copolymer salts dissolved in the water phase of the emulsions. The liquid fluid loss control additives are storable for long periods of time without settling or increasing in viscosity. When combined with hydraulic cement compositions, the emulsion additives invert whereby the NNDMA/AMPS® copolymers or salts thereof are released into the cement compositions. The additives can be prepared using known emulsion copolymerization techniques which will be described further hereinbelow.
In an alternate embodiment, the water in the water-in-oil emulsion can be removed from the emulsion leaving a substantially water free emulsion containing the NNDMA/AMPS® copolymer which can be stored for long periods of time without settling or becoming unpourable.
Thus, it is a general object of the present invention to provide methods of cementing wells using cement compositions containing liquid fluid loss control additives comprised of emulsion NNDMA/AMPS® copolymers or copolymer salts.
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, U.S. Pat. Nos. 4,515,635 and 4,555,269 issued to Rao et al. on May 7, 1985 and Nov. 26, 1985, respectively, disclose cement composition fluid loss control additives comprised of copolymers of N,N-dimethylacrylamide (NNDMA) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS®) or certain salts thereof having NNDMA to AMPS® mole ratios of between 1:4 and 4:1, respectively, and having average molecular weights of between about 75,000 and 300,000. U.S. Pat. Nos. 4,515,635 and 4,555,269 also disclose solution polymerization techniques which can be employed to obtain an aqueous solution of an NNDMA/AMPS® copolymer or copolymer salt containing 10% by weight of copolymer. Also, the patents disclose details concerning the copolymers and copolymer salts, their preparation and their use as fluid loss control additives in cement compositions. The disclosures of U.S. Pat. Nos. 4,515,635 and 4,555,269 are incorporated herein by reference.
The liquid fluid loss control additives useful in accordance with the present invention are basically comprised of a water-in-oil emulsion having a copolymer of NNDMA and AMPS® or a salt of the copolymer dissolved in the water phase of the emulsion. The additives are storable for long periods of time without settling or increasing in viscosity.
The copolymer or copolymer salt contained in an emulsion as described above can be prepared using known emulsion copolymerization techniques. Such a technique is described, for example, in U.S. Pat. No. 4,022,731 issued to Schmitt on May 10, 1997 which discloses th
Chatterji Jiten
King Bobby J.
McKinley Rita J.
Zamora Frank
Dougherty, Jr. C. Clark
Halliburton Energy Service,s Inc.
Niland Patrick D.
Roddy Craig W.
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