Patent ID: 7666821

Claim:
A self-diverting pre-flush sandstone acid treatment composition comprising water, an acid-hydrolyzable surfactant capable of forming a viscoelastic gel, the surfactant having the following amide structure: wherein R 1 is a hydrocarbyl group that may be branched or straight chained, aromatic, aliphatic or olefinic and has from about 14 to about 26 carbon atoms and may contain an amine; R 2 is hydrogen or an alkyl group having from 1 to about 4 carbon atoms; R 3 is a hydrocarbyl group having from 1 to about 10 carbon atoms; and Y is an electron withdrawing group rendering the amide group difficult to hydrolyze; an inorganic acid in an amount from about 6 to about 20 weight percent, and an organic acid in an amount from about 5 to about 20 weight percent, wherein said self-diverting composition increases in viscosity of at least about 50 cP at 170 sec −1 upon neutralization of less than about one third of the total acid, and hydrolysis of the surfactant in the gel, once formed, at a given temperature and pH takes more than at least one hour longer than the acid treatment, as determined by reduction of the viscosity of the fluid to less than 50 cP at a shear rate of 100 sec −1 .