Patent ID: 8544565

Claim:
A method of drilling into a subterranean formation comprising: introducing into a wellbore passing at least partially through the subterranean formation a fluid comprising water, at least one viscoelastic surfactant (VES) and at least one acid selected from the group consisting of organic acids, mineral acids and combinations thereof, where the VES is present in an amount effective to increase the viscosity of the fluid but for the presence of the at least one acid and where the fluid has a pH between about 2 to about 5; and at least partially consuming the at least one acid from the fluid by reaction of the at least one acid with a mineral in the subterranean formation, thereby increasing the pH of the fluid to an extent sufficient to increase the viscosity of the fluid by the action of the VES in at least a portion of the fluid to inhibit fluid loss into the formation; and where the mineral is selected from the group consisting of a carbonate, an evaporite, a salt dome, shale, and combinations thereof and further comprises at least one naturally-occurring fracture.