Method and compositions for acidizing and fracturing wells

Claim 1

A gelable acidic composition, suitable for matrix-acidizing or fracture-acidizing of a porous subterranean formation susceptible of attack by an acid and which gels upon injection into a subterranean formation, comprising: (a) water; (b) a water-thickening amount ranging from 0.2 to about 3 weight percent of a water-dispersible acrylamide-derived polymer; (c) from 0.4 to about 60 weight percent of a non-oxidizing acid which is capable of reacting with a significant amount of the acid-soluble components of said formation; and (d) from 0.001 to about 5 weight percent of at least one aldehyde precursor which hydrolyzes in aqueous acid media to produce aldehydes "in situ" which in turn react with the polymer and cause gelation of the mixture, said aldehyde precursor being selected from the group consisting of (1) acetals of an aldehyde having the formula ##STR4## wherein R 1 is selected from hydrogen, alkyl, aralkyl, alkoxyalkyl, and alkenyl groups having from 1 to about 8 inclusive carbon atoms, R 2 and R 3 can be the same or different and selected from alkyl groups having from 1 to about 4 inclusive carbon atoms with the proviso that the total number of carbon atoms in R 2 and R 3 does not exceed about 6 and n ranges from 0 to 3 (2) enol esters having the formula ##STR5## wherein R 4 is an acyl radical containing 2 to 4 carbon atoms and R 5 and R 6 are hydrogen or alkyl radicals containing 1 to 3 carbon atoms with the proviso that the total number of carbon atoms does not exceed 10 (3) reducing sugars selected from monosaccharide aldoses and disaccharides containing hemiacetal linkages (4) acetals or polyvinyl alcohols or an acetal of 1,2- or 1,3-diols containing 3 to 6 carbon atoms, and (5) cyanoacetal having the formula ##STR6## wherein R 1 represents cyanoalkyl groupings containing 3 to 7 carbon atoms, and R 2 and R 3 can be the same or different and are selected from alkyl groups having from 1 to about 4, inclusive, carboon atoms with the proviso that the total number of carbon atoms in R 2 and R 3 does not exceed about 6.

Claim 11

A method for acid-treating a porous subterranean formation susceptible of attack by an acid and penetrated by a well bore which method comprises: (1) injecting into said formation via said well bore a gelable acidic composition comprising: (a) water; (b) a water-thickening amount ranging from 0.2 to about 3 weight percent of a water-dispersible acrylamide-derived polymer; (c) from 0.4 to about 60 weight percent of a non-oxidizing acid which is capable of reacting with a significant amount of the acid-soluble components of said formation; and (d) from 0.0001 to about 5 weight percent of at least one aldehyde precursor which hydrolyzes in aqueous acid media to produce aldehydes "in situ" to react with the polymer and gels the mixture during and/or after injection into the formation, said aldehyde precursor being selected from the group consisting of (1) acetals of an aldehyde having the formula ##STR7## wherein R 1 is selected from hydrogen, alkyl, aralkyl, alkoxyalkyl, and alkenyl groups having from 1 to about 8 inclusive carbon atoms, R 2 and R 3 can be the same or different and selected from alkyl groups having from 1 to about 4 inclusive carbon atoms with the proviso that the total number of carbon atoms in R 2 and R 3 does not exceed about 6 and n ranges from 0 to 3 (2) enol ester having the formula ##STR8## wherein R 4 is an acyl radical containing 2 to 4 carbon atoms and R 5 and R 6 are hydrogen or alkyl radicals containing 1 to 3 carbon atoms with the proviso that the total number of carbon atoms does not exceed 10. (3) reducing sugars selected from monosaccharide aldoses and disaccharides containing hemiacetal linkages (4) acetals of polyvinyl alcohols or an acetal of 1,2- or 1,3-diols containing 3 to 6 carbon atoms, and (5) cyanoacetal having the formula ##STR9## wherein R 1 represents cyanoalkyl groupings containing 3 to 7 carbon atoms, and R 2 and R 3 can be the same or different and are selected from alkyl groups having from 1 to about 4, inclusive, carbon atoms with the proviso that the total number of carbon atoms in R 2 and R 3 does not exceed about 6 (2) maintaining said composition in said formation to contact therewith for a period of time sufficient to form a gelled mixture and for the acid in said composition to react significantly with the acid-soluble components of said formation and stimulate the production of fluids therefrom.

Claim 12

A method for acid-treating a porous subterranean formation susceptible of attack by an acid and penetrated by a well bore which method comprises: (1) injecting into said formation via said well bore a gelable acidic composition comprising: (a) water; (b) a water-thickening amount ranging from 0.2 to about 3 weight percent of a water-dispersible acrylamide-derived polymer; (c) from 0.4 to about 60 weight percent of a non-oxidizing acid which is capable of reacting with a significant amount of the acid-soluble components of said formation; and (d) from 0.0001 to about 5 weight percent of at least one aldehyde precursor which hydrolyzes in aqueous acid media to produce aldehydes "in situ" to react with the polymer and gels the mixture during and/or after injection into the formation, said aldehyde precursor being selected from the group consisting of (1) acetals of an aldehyde having the formula ##STR7## wherein R 1 is selected from hydrogen, alkyl, aralkyl, alkoxyalkyl, and alkenyl groups having from 1 to about 8 inclusive carbon atoms, R 2 and R 3 can be the same or different and selected from alkyl groups having from 1 to about 4 inclusive carbon atoms with the proviso that the total number of carbon atoms in R 2 and R 3 does not exceed about 6 and n ranges from 0 to 3 (2) enol ester having the formula ##STR8## wherein R 4 is an acyl radical containing 2 to 4 carbon atoms and R 5 and R 6 are hydrogen or alkyl radicals containing 1 to 3 carbon atoms with the proviso that the total number of carbon atoms does not exceed 10. (3) reducing sugars selected from monosaccharide aldoses and disaccharides containing hemiacetal linkages (4) acetals of polyvinyl alcohols or an acetal of 1,2- or 1,3-diols containing 3 to 6 carbon atoms, and (5) cyanoacetal having the formula ##STR9## wherein R 1 represents cyanoalkyl groupings containing 3 to 7 carbon atoms, and R 2 and R 3 can be the same or different and are selected from alkyl groups having from 1 to about 4, inclusive, carbon atoms with the proviso that the total number of carbon atoms in R 2 and R 3 does not exceed about 6 (2) maintaining said composition in said formation to contact therewith for a period of time sufficient to form a gelled mixture and for the acid in said composition to react significantly with the acid-soluble components of said formation and stimulate the production of fluids therefrom.