Improved oil reservoir sweep with viscoelastic surfactants

Viscoelastic surfactant solutions increase oil recovery by selectively modifying the viscosity of the injected displacing fluid in different zones of the reservoir. We demonstrate that flow resistance in high permeability zones is increased whereas no significant change in viscosity occurs in low permeability zones. This greatly reduces injected fluid losses via the high permeability route. In two phase flow in sandstones, recovery increases by about 25%. Efficiency also increases by a factor of 3 as shown by the large reduction in injected volume at breakthrough. Consequently less fluid is lost through high permeability thief zones. Recovery is increased in carbonates as well but the efficiency is depleted due to apparent changes in wetting. The reduction in injected fluid before breakthrough has the potential to prolong the economical lifespan of water wet reservoirs