METHOD OF TREATING SUBTERRANEAN FORMATIONS BY IN-SITU HYDROLYSIS OF ORGANIC ACID ESTERS
An oil or gas well penetrating a subterranean formation, such as a carbonate formation, is treated with a well treatment fluid which contains an organic ester. The fluid may be an oil-in-water emulsion of the organic ester and an emulsifier or a homogeneous solution of organic ester and a water/mutual solvent solution. Acid is produced in-situ by hydrolysis of the organic ester.
1 . A method of treating an oil or gas well penetrating a formation which comprises:
(a) introducing into the oil or gas well a well treatment fluid comprising an organic ester; and
(b) hydrolyzing the organic ester in-situ to produce acid wherein the well treatment fluid is either (i) an oil-in-water emulsion of an emulsifier and the organic ester; or (ii) a homogeneous solution of organic ester and a water/mutual solvent solution.
2 . The method of claim 1 , wherein the well treatment fluid introduced into the oil or gas well in step (a) is an emulsion of an emulsifier and the organic ester.
3 . The method of claim 2 , wherein the organic ester is an ester of an organic sulfonic acid.
4 . The method of claim 3 , wherein the ester of an organic sulfonic acid is selected from the group consisting of methyl p-toluenesulfonate, ethyl p-toluenesulfonate, methyl methanesulfonate and ethyl methanesulfonate.
5 . The method of claim 1 , wherein the oil or gas well is treated in the absence of a diverting agent.
6 . The method of claim 1 , wherein the emulsifier is non-ionic.
7 . The method of claim 1 , wherein the well is shut-in prior to hydrolysis of the organic ester.
8 . The method of claim 1 , wherein the well treatment fluid is a homogeneous solution of organic ester and a water/mutual solvent solution.
9 . The method of claim 8 , wherein the mutual solvent of the water/mutual solvent solution is selected from the group consisting of glycols, glycol ethers, terpenes, and C 3 to C 9 alcohols.
10 . The method of claim 9 , wherein the glycol is ethylene glycol monobutyl ether.
11 . A method of matrix acidizing a carbonate subterranean formation penetrated by an oil or gas well which comprises:
(a) injecting into the well a well treatment fluid comprising an organic acid ester; and
(b) hydrolyzing the organic ester in-situ to produce acid
(c) increasing the permeability of the carbonate subterranean formation wherein the well treatment fluid is either (i) an oil-in-water emulsion of an emulsifier and the organic ester; or (ii) a homogeneous solution of organic ester and a water/mutual solvent solution.
12 . The method of claim 11 , wherein the well treatment fluid injected into the well in step (a) is an emulsion of an emulsifier and the organic ester.
13 . The method of claim 12 , wherein the organic ester is an ester of an organic sulfonic acid.
14 . The method of claim 13 , wherein the ester of an organic sulfonic acid is selected from the group consisting of methyl p-toluenesulfonate, ethyl p-toluenesulfonate, methyl methanesulfonate and ethyl methanesulfonate.
15 . The method of claim 11 , wherein the well is shut-in prior to hydrolysis of the organic ester.
16 . The method of claim 11 , wherein the well treatment fluid is a homogeneous solution of organic ester and a water/mutual solvent solution.
17 . The method of claim 16 , wherein the mutual solvent of the water/mutual solvent solution is selected from the group consisting of glycols, glycol ethers, terpenes, and C 3 to C 9 alcohols.
18 . A method of matrix acidizing a carbonate formation penetrated by an oil or gas well which comprises:
(a) injecting into the well a well treatment fluid selected from the group consisting of:
(i) an oil-in-water emulsion comprising an organic acid ester and a surfactant; or
(ii) a homogeneous solution of organic acid ester in a water/mutual solvent solution;
(b) shutting-in the well;
(c) producing acid in-situ by hydrolyzing the organic acid ester; and
(d) increasing the permeability of the carbonate formation wherein the organic acid ester is selected from the group consisting of methyl p-toluenesulfonate, ethyl p-toluenesulfonate, methyl methanesulfonate and ethyl methanesulfonate.
19 . The method of claim 18 , wherein the depth of the oil or gas well is at least 15,000 feet below the surface of the earth.
20 . The method of claim 18 , wherein the well treatment fluid is an oil-in-water emulsion and further wherein the amount of organic acid ester in the emulsion is less than or equal to 10 volume percent.