Addressing Operator Concerns: Will Surfactant's Performance be Compromised Under Harsh Conditions?

Abstract

Abstract Surfactant is typically pumped during hydraulic fracturing to enhance production from unconventional reservoirs. The primary function of surfactant is believed to generate a short-lived oil-in-water (OIW) emulsion, thereby aiding oil solubilization and mobilization. Ideally, the OIW emulsion should be maintained throughout the entire liquid flow path. However, a temperature gradient typically exists from topside to the interior of the matrix, and the matrix temperature can be high. This temperature gradient is compounded by the fact that, upon dilution by the reservoir connate water, anionic surfactants typically used during fracturing, become more lipophilic at the oil-water interface because of its selective partitioning into the aqueous phase upon dilution or at high reservoir temperature. Therefore, the optimum surfactant formulation cannot be well maintained when the fracturing fluids invade the matrix and reservoir fluids begin to produce. Some nonionic surfactants, on the other hand, typically partition into the oil phase at high temperature or upon dilution. By taking those phenomena into account, an optimum surfactant-oil-water system was created by mixing both anionic and nonionic surfactants to help eliminate the effect of dilution and high reservoir temperature. The new system has been widely used in hundreds of wells in the Eagle Ford (EF) and Mississippi Lime (ML) shale, with favorable production results.