Earth boring – well treating – and oil field chemistry – Well treating – Contains organic component
Reexamination Certificate
2000-02-11
2002-10-15
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Well treating
Contains organic component
C507S225000, C507S226000, C507S227000, C526S240000, C526S287000, C526S278000
Reexamination Certificate
active
06465397
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to the preparation and use of synthetic water soluble copolymers useful in modifying the water permeability characteristics of subterranean hydrocarbon producing formations.
BACKGROUND OF THE INVENTION
Water and oil or gas often exist in the same or adjacent formations. This water is often co-produced with the desired oil or gas, leading to operational problems. As water is produced and removed from the formation, the hydrostatic pressure within the formation that is exerted on the hydrocarbon content decreases, contributing to a decline in hydrocarbon production rates. Once above ground, the produced water must be separated from the sought-after hydrocarbon. Frequently, the water exists in an emulsion with the hydrocarbon, necessitating efforts to break the emulsion and remove the water fraction. The produced water also requires storage and/or disposal, which is often time consuming and expensive.
Efforts to minimize produced water and its associated problems are addressed conventionally in the art by the use of natural, semi-synthetic, and synthetic crosslinkable polymer solutions or dispersions. Synthetic water soluble or dispersible copolymers have been successfully used for so-called water shut-off purposes as well as in relative permeability modification applications (hereinafter for short, “RPM”). These methods involve the reduction in the flow of subterraneous water in the horizons with oil and/or gas near the well-bore. The use of water shut-off polymers thus leads to a stoppage of water feeds to a production well-bore, but usually also leads to a stoppage or significant reduction in hydrocarbon production in the treated zone. The present invention is directed mainly to RPM, wherein the permeability of water in the formation is minimized without causing a significant decline in oil and/or gas permeability.
In the conventional methods, crosslinkable polymers in aqueous solutions or dispersions are pumped into underground formations and undergo swelling and crosslinking reactions to develop desired gelation characteristics. The polymer adsorbs onto the porous solids, and the gel holds water within the gel structure to alter the migration behavior and reduce the amount of produced water. Conventionally, an aqueous solution containing a crosslinkable polymer is pumped into water and hydrocarbon producing formations so that they enter water zones within and adjacent to the formations. Crosslinking materials may is either be injected along with the crosslinkable polymer solution, or injected after the polymer has been injected.
The art includes various techniques and chemistries for achieving the desired subterranean swelled, crosslinked gels of the polymer solutions, generally leading to the formation of substrate-adhered gels which reduce or stop, as the intended result, the flow of water through the natural fractures and high permeability streaks in the formations.
Early examples of synthetic polymers are the partially hydrolyzed polyacrylamides possessing pendant carboxylate groups reactive with external crosslinking agents. Thermally stable, crosslinkable, carboxylate-containing polymers of acrylamide; copolymers of N-vinyl-2-pyrrolidone and acrylamide; terpolymers of sodium-2-acrylamido-2-methyl-propanesulfonate, acrylamide, and N-vinyl-2-pyrrolidone; and copolymers of sodium-2-acrylamido-2-methyl-propanesulfonate, acrylamide, and vinylacylamide have been suggested for use with an external crosslinking system to treat subterranean formations with high salinity and at elevated temperatures.
In the conventional method of altering the permeability of water in underground formations, the crosslinkable polymers are injected into a formation simultaneously with a selected crosslinking system, each typically in the form of aqueous solutions. The solutions permeate into the regions having the highest water permeability, crosslinking reactions proceed over the course of hours, resulting in an aqueous, (swelled) gel. Thermosetting phenol-aldehyde polymers are exemplary crosslinking systems used in combination with water-soluble crosslinkable polymer. Other crosslinking agents include multivalent metal compounds reactive with carboxyl-containing copolymers, for example, complexed chromium, zirconium, or titanium compounds. Complexing ligands are sometimes also utilized and are effective in delaying the onset of gelation.
Use is often made of polymers that are introduced in a solution into the porous formations, absorbed at the solid surfaces and penetrate into the pores so that they are suitable for reducing the water influx by friction.
U.S. Pat. No. 4,095,651 discloses the use of hydrolyzed polyacrylamides. It has been found, however, that this polymer type is mainly effective for water with a low salt content and breaks down in water with a higher salt content. In the presence of polyvalent ions these polymers have a tendency at high temperatures to form precipitates that can clog the pores of the rock formations.
U.S. Pat. No. 4,507,440 discloses water soluble polymers for enhanced petroleum recovery which are crosslinkable on addition of acid, resulting in crosslinks of the —NR—CH═N—CO— type. These polymers are employed in acidizing-stimulation of underground oil and gas formations. The polymers contain copolymerized acrylamide and formyl-amido-type comonomers. Thus, in-situ (underground) crosslinking in the well bore-hole occurred by co-injection of aqueous 15 wt. % HCl containing a mixture of water soluble copolymers, one being a copolymer of 2-acrylamido-2-methylpropanesulfonic acid-acrylamide-N-vinyl-N-methylacetamide and the other being acrylic acid-vinyl formamide-vinyl pyrrolidone copolymer. The crosslinked polymer gels are stable for days at 20-30° C. in acid media, but are easily hydrolyzed at 80-90° C.
U.S. Pat. No. 4,718,491 discloses the use of polysaccharides. These compounds, which are difficult to inject into the pore space, do effect a retardation or reduction of the water influx, but they allow only incomplete exploitation of the hydrocarbon deposits. They have been known to lose their effect at high temperatures.
U.S. Pat. No. 4,842,971 discloses the use of non-hydrolyzed acrylamide polymers or copolymers which are hydrolyzed by the subsequent introduction of an aqueous basic solution. This process has some drawbacks in terms of additional work for introducing a further solution in the well-bore and difficulties attendant in reaching the injected polymer solution by subsequent application of the basic solution. Corrosion of equipment from basic solutions are known. In addition, the efficacy of the polymer solution is contingent upon the extent of hydrolytic conversion by the basic solution.
Other examples of conventional methods and materials include those disclosed in U.S. Pat. No. 5,547,025. Therein, carboxylate-containing, water swellable polymers capable of gelling in the presence of crosslinking agent such as, for example, a multivalent metallic compound are exemplified.
U.S. Pat. No. 5,379,841 discloses methods for reducing or stopping water inflow from a deposit with the use of a copolymer comprising 2-acrylamido-2-methylpropane sulfonate and vinylacylamide, with optional anionic or cationic comonomers. The molecular weight of the copolymers can range from 50 thousand to 20 million. Optional anionic or cationiccomonomers are suggested for desired increased adhesion to different substrates. For formations in which pore diameters are smaller, molecular weights of the copolymer are suggested to be in the range of 50,000 to 3 million, and for formations having relatively larger diameter pore sizes, a molecular weight in the range of 3 to 20 million is suggested.
U.S. Pat. No. 5,701,956 teaches the use of a graft copolymer of a hydrophilic polymer and a phosphonate as a crosslinkable aqueous polymer in brine. The latent crosslinking function is selective to the water phase and not the oil phase. Polymer compositions for which phosphonate functional compounds are grafted thereto include polyacrylamide, c
Clariant Finance (BVI) Limited
Silverman Richard P.
Tucker Philip
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