Generating Acid Downhole in Acid Fracturing

A method of acid fracturing a subterranean formation penetrated by a wellbore comprising:

• a) injecting into the formation a fluid comprising particles of a solid acid-precursor at a concentration between about 0.05 and about 0.6 kg/L, at a pressure sufficient to fracture the formation, said fluid not viscosified with a viscoelastic surfactant, and
• b) allowing at least a portion of the solid acid-precursor to hydrolyze, wherein the solid acid-precursor is coated with a hydrolysis-delaying material.

A method of acid fracturing a subterranean formation penetrated by a wellbore comprising:

• a) injecting into the formation a fluid comprising particles of a solid acid-precursor at a concentration between about 0.05 and about 0.6 kg/L, at a pressure sufficient to fracture the formation, said fluid not viscosified with a viscoelastic surfactant, and
• b) allowing at least a portion of the solid acid-precursor to hydrolyze, wherein the fluid further comprises a water-soluble agent that accelerates hydrolysis of the solid acid-precursor, said agent selected from the group consisting of esters, diesters, anhydrides, lactones, alkali metal alkoxides, carbonates, bicarbonates, alcohols, alkali metal hydroxides, ammonium hydroxide, amides, amines, alkanol amines and mixtures thereof.

A method of acid fracturing a subterranean formation penetrated by a wellbore comprising:

• a) injecting into the formation a fluid comprising particles of a solid acid-precursor at a concentration between about 0.05 and about 0.6 kg/L, at a pressure sufficient to fracture the formation, said fluid not viscosified with a viscoelastic surfactant, and
• b) allowing at least a portion of the solid acid-precursor to hydrolyze, wherein the fluid further comprises an acid selected from the group consisting of hydrochloric acid, hydrofluoric acid, ammonium bifluoride, formic acid, acetic acid, lactic acid, glycolic acid, aminopolycarboxylic acids, polyaminopolycarboxylic acids, salts thereof and mixtures thereof.