Viscoelastic Surfactant based Self-diverting Acid for Enhanced Stimulation in Carbonate Reservoirs

摘要

An improved viscoelastic surfactant (VES) based selfdivertingrnacid system has been developed for matrix treatmentrnof carbonate formations. The self-diverting acid contains arnnovel viscoelastic surfactant that undergoes an increase inrnviscosity as the fluid penetrates carbonate formations. Therndecrease in acid concentration as the acid reacts with therncarbonate rocks promotes the transformation of sphericalrnmicellar structure into a worm-like structure that imparts highrnviscosity to the fluid. The highly viscous fluid acts as arntemporary barrier to reduce further fluid loss into thernwormholes and allows complete stimulation of all treatingrnzones. After acid treatment, the viscous fluid is broken byrneither formation hydrocarbons or pre-flush fluids. The VESrnbased self-diverting acid contains no solids, so there is nornbridging when it is pumped through tubing. Rheologicalrnstudies showed that the acid rapidly developed viscosity as thernacid was spent with CaCO_3, and the spent fluid was stable uprnto 300oF. Diversion tests using multiple-core flood equipmentrnshowed effective wormholing in both high permeability andrnlow permeability cores. The effectiveness of the new systemrnin diversion and stimulation was confirmed in more than 70rnfield applications, both through increased well production andrn/or injection and production logs.