Controlled release of acid in a wellbore penetrating a carbonaceous formation

Abstract

A method for controlled release of acid in a subterranean carbonaceous formation is achieved by placing in the openhole section of a wellbore within the formation a crosslinked acid of a volume substantially equal to the volume of the openhole section, then using tubing placed within the openhole section to circulate into the crosslinked acid a composition containing a breaker for the crosslinked acid at a matrix rate while removing the tubing from the openhole section, breaking the crosslinked acid while the tubing is removed, closing the backside and squeezing the uncrosslinked acid into the subterranean carbonaceous formation. In one non-limiting embodiment the openhole section may be substantially horizontal.

What is claimed is: 
     
         1 . A method for controlled release of acid in a subterranean carbonaceous formation having a wellbore with at least one openhole section having a bottom or toe, where the wellbore has a backside, the method comprising not necessarily in this order:
 placing in the openhole section a crosslinked acid in a volume substantially equal to the volume of the openhole section;   using tubing placed within the openhole section, circulating into the openhole section a composition at a rate, where the composition comprises a breaker for the crosslinked acid beginning proximate to the bottom or toe of the openhole section;   breaking the crosslinked acid to give uncrosslinked acid;   removing the tubing from the openhole section;   closing the backside; and   squeezing the uncrosslinked acid into the subterranean carbonaceous formation.   
     
     
         2 . The method of  claim 1  where the crosslinked acid has an absence of an internal breaker. 
     
     
         3 . The method of  claim 1  where removing the tubing from the openhole section and squeezing the uncrosslinked acid into the subterranean carbonaceous formation occur essentially simultaneously. 
     
     
         4 . The method of  claim 1  where the crosslinked acid is crosslinked hydrochloric acid. 
     
     
         5 . The method of  claim 4  where the proportion of acid in the crosslinked acid ranges from about 7.5 to about 28 wt %. 
     
     
         6 . The method of  claim 1  where the breaker is a fluoride solution in an amount effective to substantially break the crosslinked acid, and where the fluoride solution comprises between about 3 to about 5 wt % fluoride. 
     
     
         7 . The method of  claim 1  where the composition additionally comprises a weak acid solution where the acid is present in the composition in a concentration between about 3 to about 5 wt %, and where the acid may be the same or different as the acid of the crosslinked acid. 
     
     
         8 . The method of  claim 6  where the acid in the weak acid solution is hydrochloric acid. 
     
     
         9 . The method of  claim 1  where the composition is circulated at a matrix rate. 
     
     
         10 . The method of  claim 1  where:
 circulating into the openhole section a composition; 
 breaking the crosslinked acid to give uncrosslinked acid; 
 removing the tubing from the openhole section; and 
 squeezing the uncrosslinked acid into the subterranean carbonaceous formation; 
 all occur essentially simultaneously. 
 
     
     
         11 . The method of  claim 1  where the uncrosslinked acid is more evenly distributed into the subterranean carbonaceous formation as compared with a method where tubing is not removed during the method. 
     
     
         12 . The method of  claim 1  where the openhole section is substantially horizontal. 
     
     
         13 . A method for controlled release of acid in a subterranean carbonaceous formation having a wellbore with at least one substantially horizontal openhole section having a bottom or toe, where the wellbore has a backside, the method comprising:
 placing in the substantially horizontal openhole section a crosslinked acid of a volume substantially equal to the volume of the substantially horizontal openhole section, in an absence of an internal breaker;   using tubing placed within the substantially horizontal openhole section, circulating into the substantially horizontal openhole section a composition at a matrix rate, where the composition comprises a weak acid and a breaker for the crosslinked acid, beginning proximate to the bottom or toe of the substantially horizontal openhole section while removing the tubing from the substantially horizontal openhole section, where the acid may be the same or different as the acid of the crosslinked acid and where the acid is present in the composition in a concentration between about 3 to about 5 wt %;   breaking the crosslinked acid while the tubing is removed, to give uncrosslinked acid;   closing the backside; and   squeezing the uncrosslinked acid into the subterranean carbonaceous formation.   
     
     
         14 . The method of  claim 13  where the crosslinked acid is crosslinked hydrochloric acid. 
     
     
         15 . The method of  claim 14  where the proportion of acid in the crosslinked acid ranges from about 7.5 to about 28 wt %. 
     
     
         16 . The method of  claim 13  where the breaker is a fluoride solution in an amount effective to substantially break the crosslinked acid, and where the fluoride comprises between about 3 to about 5 wt % fluoride. 
     
     
         17 . The method of  claim 13  where the acid in the composition is hydrochloric acid. 
     
     
         18 . The method of  claim 13  where the uncrosslinked acid is more evenly distributed into the subterranean carbonaceous formation as compared with a method where tubing is not removed during the method. 
     
     
         19 . A method for controlled release of acid in a subterranean carbonaceous formation having a wellbore with at least one openhole section having a bottom or toe, where the wellbore has a backside, the method comprising:
 placing in the openhole section a crosslinked acid of a volume substantially equal to the volume of the openhole section and a composition;   closing the backside; and   
       essentially simultaneously:
 using tubing placed within the openhole section, circulating into the openhole section a composition at a rate, where the composition comprises a breaker for the crosslinked acid beginning proximate to the bottom or toe of the openhole section; 
 breaking the crosslinked acid to give uncrosslinked acid; 
 removing the tubing from the openhole section; and 
 squeezing the uncrosslinked acid into the subterranean carbonaceous formation. 
 
     
     
         20 . The method of  claim 19  where the crosslinked acid is crosslinked hydrochloric acid, and where the proportion of acid in the crosslinked acid ranges from about 7.5 to about 28 wt %. 
     
     
         21 . The method of  claim 19  where the breaker is a fluoride solution in an amount effective to substantially break the crosslinked acid between about 3 to about 5 wt % fluoride.