Patent ID: 7575054

Claim:
A method of treating a subterranean sandstone formation penetrated by a wellbore comprising injecting into the formation a treatment fluid having a viscosity of less than about 20 cP comprising at least one viscoelastic surfactant selected from the group consisting of cationic viscoelastic surfactants, zwitterionic viscoelastic surfactants, and mixtures thereof, at a viscoelastic surfactant concentration insufficient for aggregation of viscoelastic surfactant structures to form a viscoelastic fluid, a hydrogen fluoride source selected from the group consisting of ammonium fluoride, ammonium bifluoride, polyvinylammonium fluoride, polyvinylpyridinium fluoride, pyridinium fluoride, imidazolium fluoride, sodium tetrafluoroborate, ammonium tetrafluoroborate, salts of hexafluoroantimony, synthetic resinous fluorine-containing polymer, and mixtures thereof, and at least one formation-dissolving agent, wherein the viscosity of the treatment fluid increases to above about 50 cP as the fluid passes through the formation.