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Compositions containing a buffer and a peroxide or peracid useful for treating wellsRelated Patent Categories: Wells, Processes, With Indicating, Testing, Measuring Or Locating, Permeability DeterminingCompositions containing a buffer and a peroxide or peracid useful for treating wells description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070163779, Compositions containing a buffer and a peroxide or peracid useful for treating wells. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATIONS [0001] The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/413,181 filed Sep. 24, 2002, the contents of which are incorporated herein by reference. BACKGROUND OF INVENTION [0002] 1. Field of the Invention [0003] A family of mud removal systems for the simultaneous removal of all polymer-based drilling fluid damage is disclosed. The damage can include that caused by partially-hydrolyzed polyacrylamide (PHPA) polymer and particulates such as calcium carbonate. The systems are based on the synergistic combination of organic salt buffers and either peroxides or per-acids. The systems can also include catalase enzymes. [0004] 2. Description of Related Art [0005] Many wells are damaged in the course of drilling and workover by the use of drilling muds, drill-in fluids, kill fluids and kill-pills that contain, amongst other things, polymeric constituents. The latter may consist of a single polymer or may consist of mixtures of polymers in aqueous solution/suspension. These polymers may be added for the purposes of viscosification, leak-off control, lubrication, friction reduction and control of shales or other active clays. Typically, the polymers used for such purposes include xanthans (exo-polymers produced by Xanthomonas Camperstris and its relatives), starches (produced from corn, potato, etc), celluloses, guars, and derivatives of these main groups. Polyacrylamides may also be used, in particular so-called partially-hydrolyzed polyacrylamide (PHPA), which is used for shale encapsulation. In addition, most of these fluids contain some form of particulate to impart density and to improve fluid-loss control. The most common of these particulates is calcium carbonate although, occasionally, salt or barite may be used. [0006] Subsequent well productivity can be significantly impaired by the use of these mixtures of polymers and particulate materials, due to the persistence of residues in the well. Their removal can result in substantial improvements in production. Historically, removal of these materials has involved the use of soaking with strong mineral acids (e.g. hydrochloric acid), strong organic acids (e.g. sulphamic acid), or oxidizing agents (e.g. sodium hypochlorite or lithium hypochlorite). More recently, enzymes have been used to remove the polymeric constituents. Some polymers, however, are largely immune to enzymatic degradation (e.g. PHPA). [0007] Acids can hydrolyze some polymers, and can dissolve calcium carbonate. However, in practice, calcium carbonate is often coated with polymer residue, and its removal has been shown to be non-uniform, possible due to wormholing of the acid through the cake. This results in non-optimal inflow performance, with higher drawdowns and, potentially, greater risk of early water breakthrough, fines migration, and formation failure. Additionally, the acid is corrosive and inefficient, and large volumes must be used in extended reach wells. While hypochlorites can destroy most polymers, they will not dissolve calcium carbonate and their high pH can cause problems if the formation contains any sensitive clays. Combining acids and hypochlorites generates chlorine gas, a potentially harmful material. Accordingly, prior treatments designed to target both polymers and calcium carbonate consisted of several steps. This complicates the operation, and causes additional expense due to the time involved. [0008] Thus, there exists a need for clean-up compositions and methods that are effective at removing both polymer deposits and calcium carbonate. The methods preferably accomplish the removal of both materials in a single step. SUMMARY OF INVENTION [0009] Compositions comprising buffered hydrogen peroxide or per-acids are attractive for use in treating oil and/or gas wells that contain polymer deposits or calcium carbonate. An example per-acid is peroxyacetic acid. The compositions can further comprise enzymes such as peroxidases. Methods for treating wells can be performed as single step treatments. DETAILED DESCRIPTION [0010] Compositions and methods have been identified that are capable of removing all polymers encountered thus far while, simultaneously, dissolving calcium carbonate. The treatment methods include a single step treatment of a well, effective at reducing or eliminating the presence of polymer deposits and calcium carbonate. The methods improve the permeability of the well, preferably to at least the level observed prior to formation of polymer deposits. Compositions [0011] One embodiment of the invention relates to well treatment compositions. The compositions can comprise, consist essentially of, or consist of water, a buffer, and hydrogen peroxide and/or a per-acid. The composition can further comprise iron-control agents, surface tension reducers, dispersants, corrosion inhibitors, clay stabilizers, and other components useful in treating wells. [0012] The water can generally be from any source. The water can be fresh water, brackish water, or salt water. The compositions can generally have any pH. For example, the pH can be about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, or ranges between any two of these values. It is presently preferred that the pH be about 3.0 to about 5.0. [0013] The buffer can generally be any buffer system. Buffers commonly are a combination of an acid and its salt. For example, a buffer can comprise acetic acid and an acetate salt (such as sodium acetate, potassium acetate, or ammonium acetate), formic acid and a formate salt (such as sodium formate, potassium formate, or ammonium formate), citric acid and a citrate salt (such as sodium citrate, potassium citrate, or ammonium citrate), and other acid / salt buffer combinations. The buffer system can generally be present at any concentration. The buffer system can be present at a concentration of about 1 weight percent to about 30 weight percent. Example concentrations include about 1 weight percent, about 5 weight percent, about 10 weight percent, about 15 weight percent, about 20 weight percent, about 25 weight percent, about 30 weight percent, and ranges between any two of these values. [0014] Hydrogen peroxide can generally be present in the composition at a concentration of about 1 weight percent to about 6 weight percent. Example concentrations include about 1 weight percent, about 2 weight percent, about 3 weight percent, about 4 weight percent, about 5 weight percent, about 6 weight percent, and ranges between any two of these values. A concentration of about 3 weight percent to about 5 weight percent is presently preferred. The per-acid can generally be any per-acid. Examples of per-acids include peracetic acid, performic acid, perpropanoic acid, and perbutanoic acid. It is presently preferred that the per-acid be peroxyacetic acid (ethaneperoxoic acid; peroxyacetic acid; CH.sub.3CO.sub.3H). The per-acid can generally be present in the composition at a concentration of about 1 weight percent to about 15 weight percent, with a concentration of about 3 weight percent to about 10 weight percent being presently preferred. Examples of concentrations include about 1 weight percent, about 2 weight percent, about 3 weight percent, about 4 weight percent, about 5 weight percent, about 6 weight percent, about 7 weight percent, about 8 weight percent, about 9 weight percent, about 10 weight percent, about 11 weight percent, about 12 weight percent, about 13 weight percent, about 14 weight percent, about 15 weight percent, and ranges between any two of these values. The compositions can comprise both hydrogen peroxide and a per-acid, or hydrogen peroxide and an organic acid (such as acetic acid, formic acid, propanoic acid, or butanoic acid). [0015] The composition can further comprise accelerants or inhibitors to modify the rate of reaction with polymer deposits or calcium carbonate. Accelerants increase the rate of decomposition of peroxides. Examples of accelerants include peroxidase enzymes, and transition metal compounds (e.g. compounds of manganese, iron, copper, etc.). Accelerants can generally be present in the composition at a concentration of about 1-2 ppm to about 1-2 weight percent. Inhibitors decrease the rate of decomposition of peroxides. Examples of inhibitors include phosphate salts and phosphonate salts. Inhibitors can generally be present in the composition at a concentration of about 1-2 ppm to about 5 weight percent. Methods of Use [0016] The above described compositions are useful for treating oil and/or gas wells suspected of containing polymer deposits and/or calcium carbonate. Useful compositions include those comprising water, a buffer, and hydrogen peroxide and/or a per-acid. Alternatively, the methods can involve the use of a composition comprising water and hydrogen peroxide. [0017] The methods can comprise selecting an oil and/or gas well, and pumping one of the above described compositions into the well. The compositions are contacted with the well for a period of time sufficient to reduce or eliminate any polymer deposits and/or calcium carbonate. The methods can further comprise removing the compositions after the contacting period. The well is preferably treated with the compositions are in a single step. [0018] The pumping can be performed in a single pumping event, multiple pumping events, or as a continuous pumping process. The well can be "closed in", allowing the compositions to contact the well for a period of time during which additional pumping or drilling is not performed. Continue reading about Compositions containing a buffer and a peroxide or peracid useful for treating wells... 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