Multiphase Permeability Evolution in Low Permeability Sandstones from Surfactant-Treated Fractring Fluids

Improper selection and design of surfactant treatments intended to remove damage aqueous phase trapping often ends up causing other types of formation damage. This is due to our limited understanding of the processes that govern rock-fluid and fluid-fluid interactions between surfactants, fracturing fluid and the formation during invasion and flowback of the injected fluids in the rock matrix. This study focuses on the laboratory investigation of the processes governing multiphase permeability evolution during invasion of fracturing fluids treated with surfactants in low permeability sandstones. Two surfactant chemicals, Triton X-100, a hydrocarbon surfactant and Novec FC-4430, a fluorosurfactant, were used to treat filtrate from slickwater, linear gel and borate crosslinked gel fluids. Multiphase experiments were conducted on sandstones cores flooded with the treated fluids. The experiments consist of steady state gas displacements and pulse decay permeability measurements. The obtained data include gas flow rate, pore volumes of liquid expelled and gas relative permeability curves. Experimental results indicate that treatments with fluorosurfactant improved liquid and gas permeability recovery for all fracturing fluids. Additionally, maximum liquid and gas permeability recovery was achieved when the core was pretreated with fluorosurfactant. Our results show that multiphase permeability evolution with surfactant treatment is driven by wettability alterations rather than reduction in interfacial tension. Multiphase permeability data could be used in modeling of post fracture well performance and formation damage assessment in low permeability sandstones. The new findings will serve as a guide for optimizing fracturing fluid/surfactant treatment in tight gas reservoirs.