Wells – Processes – Cementing – plugging or consolidating
Reexamination Certificate
1998-12-15
2001-03-06
Suchfield, George (Department: 3672)
Wells
Processes
Cementing, plugging or consolidating
C166S270000, C166S300000, C507S224000, C507S226000, C507S271000, C507S272000, C507S277000, C507S903000
Reexamination Certificate
active
06196317
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods and compositions for reducing the permeabilities of subterranean zones, and more particularly, to improved water soluble polymeric compositions which form cross-linked gels in the zones.
2. Description of the Prior Art
When wells penetrating oil and gas producing subterranean formations are produced, water often accompanies the oil and gas. The water can be the result of a water producing zone communicated with the oil and gas producing formation by fractures, high permeability streaks and the like, or it can be caused by a variety of other occurrences which are well known to those skilled in the art such as water coning, water cresting, bottom water, channeling at the well bore, etc.
In enhanced recovery techniques such as water flooding, an aqueous flood or displacement fluid is injected under pressure into an oil containing subterranean formation by way of one or more injection wells. The flow of the aqueous fluid through the formation displaces oil contained therein and drives it to one or more producing wells. However, the aqueous displacement fluid often flows through the most permeable zones in the subterranean formation whereby less permeable zones containing oil are bypassed. This uneven flow of the aqueous displacement fluid through the formation reduces the overall yield of hydrocarbons from the formation.
Heretofore, enhanced recovery problems in a subterranean oil containing formation caused by permeability variations therein have been corrected by reducing the permeability of the subterranean formation flow paths having high permeability and low oil content. As a result, the subsequently injected aqueous displacement fluid is forced through flow paths having low permeability and high oil content. The techniques utilized to accomplish this high flow path permeability reduction, referred to in the art as “conformance control techniques,” have included injecting aqueous solutions of polymers and gelling agents into the high permeability flow paths whereby the polymers are gelled and cross-linked therein. For example, water soluble polymers including copolymers of acrylamide and acrylic acid cross-linked with chromium or other transition metal ions have been utilized heretofore. In accordance with an early technique, an aqueous solution of one or more of the polymers or copolymers mixed with a cross-linking metal ion is injected into the subterranean formation and allowed to cross-link therein. However, it has heretofore been found that the cross-linked gels formed have often been ineffective at high temperatures, i.e., at temperatures above about 80° C. because of the instability of the cross-linker or polymer. This has resulted in uncontrolled cross-linking rates (too rapid), cross-linker precipitation, polymer degradation, or an inefficient solution propagation. In attempts to correct these problems, the cross-linking metal ion has been coordinated with a ligand such as acetate or propionate to slow the reaction of the metal ion with the polymer. While this and other techniques have been utilized successfully, the use of some metal ions, e.g., chromium, has adverse environmental effects, and the metal ion used can be adsorbed by formation materials whereby it is prevented from functioning to cross-link the polymer.
U.S. Pat. No. 4,773,481 to Allison et al. issued on Sep. 27, 1988 describes a process for reducing the permeability of a subterranean formation by the cross-linking of water soluble polymers of polyalkylene imines and polyalkylenepolyamines with certain polymers which are anionic or hydrolyzable to form anionic polymers. Examples of the anionic polymers are polyacrylamide and alkylpolyacrylamides, copolymers of polyacrylamide and alkylpolyacrylamides with ethylene, propylene and styrene, polymaleic anhydride and polymethylacrylate and hydrolysis products thereof. As described in the patent, when the water-soluble polymer and the anionic polymer are mixed, a viscous gel is quickly formed. In use, a solution of the water-soluble polymer is pumped into the subterranean formation first, followed by water to displace the water soluble polymer from the well bore to thereby prevent premature gelling upon introduction of the anionic polymer. Thereafter, the anionic polymer is pumped into the formation. This three step procedure has a number of disadvantages in practice and is costly to perform, but it is necessary because the water soluble polyalkylene imine or polyalkylenepolyamine reacts very quickly with the anionic polymer and cannot be premixed without premature gelation.
Thus, there are continuing needs for improved methods and compositions for reducing the permeabilities of subterranean zones using water soluble polymeric components whereby the cross-linking of the components is effectively and simply controlled at high temperatures.
SUMMARY OF THE INVENTION
The present invention provides methods and compositions for reducing the permeabilities of subterranean zones at high temperatures which meet the needs described above and overcome the deficiencies of the prior art.
The methods of the present invention basically comprise the steps of introducing an aqueous solution of a chelated organic gelling agent and a copolymer of an ethylenically unsaturated polar monomer and an ethylenically unsaturated ester into a subterranean zone, and then allowing the aqueous solution to form a cross-linked gel in the zone. The chelated organic gelling agent is comprised of a water soluble polyalkylene imine chelated with a metal ion, preferably polyethylene imine chelated with zirconium. The ethylenically unsaturated polar monomer in the copolymer is an amide of an unsaturated carboxylic acid, preferably acrylamide, and the ethylenically unsaturated ester in the copolymer is formed of a hydroxyl compound and an ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid and the like. A preferred unsaturated ester is t-butyl acrylate.
In a further aspect of the present invention, instead of utilizing the above described copolymer which is rapidly cross-linked by the chelated gelling agent once the chelated gelling agent disassociates, the copolymer can be stabilized whereby it does not cross-link as rapidly at high temperatures and also has greater long term gel strength after being cross-linked by forming it into a terpolymer or a tetrapolymer. That is, instead of a copolymer, the above described ethylenically unsaturated polar monomer, preferably acrylamide, and the ethylenically unsaturated ester, preferably t-butyl acrylate, are reacted with AMPS®(2-acrylamido-2-methylpropane sulfonic acid) and/or N-vinylpyrrolidone to produce a terpolymer, e.g., polyacrylamide/t-butyl acrylate/AMPS® or polyacrylamide/t-butyl acrylate/N-vinylpyrrolidone or a tetrapolymer, e.g., polyacrylamide/t-butyl acrylate/AMPS®/N-vinylpyrrolidone. The most preferred terpolymer is polyacrylamide/t-butyl acrylate/N-vinylpyrrolidone.
The compositions of this invention for reducing the permeability of a subterranean zone are basically comprised of water, a copolymer of an ethylenically unsaturated polar monomer and an ethylenically unsaturated ester or a terpolymer or tetrapolymer of the aforesaid polar monomer and ester with AMPS® and/or N-vinylpyrrolidone, and a chelated organic gelling agent.
It is, therefore, a general object of the present invention to provide improved methods and polymeric compositions for reducing the permeabilities of subterranean zones.
REFERENCES:
patent: 3697498 (1972-10-01), Browning et al.
patent: 4461351 (1984-07-01), Falk
patent: 4655942 (1987-04-01), Dickert, Jr. et al.
patent: 4664713 (1987-05-01), Almond et al.
patent: 4773481 (1988-09-01), Allison et al.
patent: 4799550 (1989-01-01), Harris et al.
patent: 5133408 (1992-07-01), Tackett
patent: 5146986 (1992-09-01), Dalrymple
patent: 5161615 (1992-11-01), Hutchins et al.
patent: 5181568 (1993-01-01), McKown et al.
patent: 5246073 (1993-09-01), Sandiford et al.
patent: 5304620 (1994-04-01), Holtmyer et
Dougherty, Jr. C. Clark
Halliburton Energy Service,s Inc.
Kent Robert A.
Suchfield George
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