Process for treatment of underground formations

Abstract

A process for treating an underground formation, which process comprises: (a) introducing into the underground formation a treatment fluid comprising an organic acid precursor; (b) heating a zone within the formation, which zone contains at least a portion of the organic acid precursor, to a temperature which is above the natural formation temperature and sufficient to increase the rate of hydrolysis of the organic acid precursor; and (c) allowing the organic acid precursor to hydrolyse to produce an organic acid in an amount effective to acidize the underground formation.

1 . A process for treating an underground formation, which process comprises:
 (a) introducing into the underground formation a treatment fluid comprising an organic acid precursor;   (b) heating a zone within the formation, which zone contains at least a portion of the organic acid precursor, to a temperature which is above the natural formation temperature and sufficient to increase the rate of hydrolysis of the organic acid precursor; and   (c) allowing the organic acid precursor to hydrolyse to produce an organic acid in an amount effective to acidize the underground formation.   
     
     
         2 . A process according to  claim 1  wherein the organic acid precursor is an ester, orthoester, anhydride, polyester or polyorthoester. 
     
     
         3 . A process according to  claim 1  wherein, in step (b), heating is achieved using hot watering, hot oiling, steam injection, closed circuit heating, exothermic chemical reactions, microwave heating, electric heating, controlled combustion or oxidation, or a heat exchange compressor. 
     
     
         4 . A process according to  claim 1  which process further comprises introducing one or more polymer breakers into the formation to achieve polymer breaking in combination with acidizing. 
     
     
         5 . A process according to  claim 1  which process further comprises introducing one or more of an enzyme catalyst, non-enzyme catalyst and carboxylate compound into the formation to further increase the rate of production of acid from the organic acid precursor. 
     
     
         6 . A process according to  claim 1  wherein, in step (b), heating is provided by a source of heat which is moveable within the wellbore or formation. 
     
     
         7 . A process according to  claim 1  wherein the underground formation is a hydrocarbon or water reservoir and the process further comprises recovering a hydrocarbon or water from the treated reservoir. 
     
     
         8 . A process according to  claim 7  wherein the hydrocarbon is oil or gas. 
     
     
         9 . A process according to  claim 1  wherein the organic acid precursor is an ester of a carboxylic acid or of a hydroxycarboxylic acid. 
     
     
         10 . A process according to  claim 9  wherein the ester is an ester of an aliphatic carboxylic acid of formula RCO 2 H wherein R is selected from hydrogen, an alkyl group having from 1 to 6 carbon atoms and —R′—CO 2 H where R′ is a bond or an alkylene group having from 1 to 6 carbon atoms, the said alkyl or alkylene group being branched or unbranched and unsubstituted or substituted 
     
     
         11 . A process according to  claim 9  wherein the ester is a carboxylic acid ester of 1,2,3-propanetriol, ethylene glycol, diethylene glycol or triethylene glycol. 
     
     
         12 . A process according to  claim 9  wherein the ester is an ester of acetic acid, formic acid, lactic acid or glycolic acid. 
     
     
         13 . A process according to  claim 1  wherein the organic acid precursor is an aliphatic polyester. 
     
     
         14 . A process according to  claim 13  wherein the aliphatic polyester comprises one or more of lactic acid, lactide, glycolic acid, glycolide, caprolactone and (optionally) compounds which may condense with lactic acid, lactide, glycolic acid, glycolide or caprolactone. 
     
     
         15 . A process according to  claim 4  wherein the polymer breaker is an enzyme 
     
     
         16 . A process according to  claim 15  wherein the polymer breaker is an enzyme which can degrade starch, xanthan, cellulose, guar, scleroglucan or succinoglycan, or derivatives of these polymers. 
     
     
         17 . A process according to  claim 4  wherein the polymer breaker is an oxidant. 
     
     
         18 . A process according to  claim 17  wherein the polymer breaker is a persulphate, hypochlorite, peroxide, perborate, percarbonate, perphosphate, persilicate, a metal cation or a hydrogen peroxide adduct. 
     
     
         19 . A process according to  claim 1  any one of the preceding claims wherein the treatment fluid is introduced into the reservoir via a wellbore which extends to the reservoir. 
     
     
         20 . A process according to  claim 19  wherein the wellbore is vertical, deviated, inclined or horizontal. 
     
     
         21 . A process according to  claim 1  wherein the treatment fluid is introduced into the reservoir via the drillstring, coiled tubing or by bullheading. 
     
     
         22 . A process according to  claim 1  wherein the treatment fluid is used as the base fluid for a gravel packing operation. 
     
     
         23 . A process according to  claim 1  wherein at least one of any polymer breaker, enzyme or non-enzyme catalyst is present in the form of a delayed release preparation. 
     
     
         24 . A process according to  claim 1  wherein acid is produced in an amount effective to dissolve acid soluble material in the underground formation. 
     
     
         25 . A process according to  claim 1  wherein acid is produced in an amount effective to increase the rate of production or infectivity of wells drilled into the formation. 
     
     
         26 . A process according to  claim 1  wherein acid is produced in an amount effective to increase the permeability of the formation, treat filter cake, treat a biofilm, break a pH-sensitive cross-linked gel or disrupt mixed metal hydroxides or complexes of mixed metal hydroxides. 
     
     
         27 . A process according to  claim 1  wherein acid is produced in an amount effective to treat an induced or natural fracture or a natural fracture network.