Mitigating near-fracture blockage and enhancing oil recovery in tight reservoirs by adding surfactants in hydraulic fracturing fluid

Flowback after hydraulic fracturing consistently shows a significantly poor load recovery of the fracturing fluid. The unrecovered fluid creates a blockage at the matrix-fracture interface in the reservoir, which hinders the optimum hydrocarbon production. Surfactant, added into the fracturing fluid, is believed to minimize this blockage by reducing the oil-water interfacial tension (IFT) and altering the rock wettability. Although many lab and field data have shown the surfactant benefits, there is a lack of mechanistic analysis on how surfactant more effectively removes such blockage. Therefore, this paper presents a mechanistic study of water blockage removal by surfactant. Interfacial tension (IFT) reduction and wettability alteration effect are modeled to represent the main effects induced due to the surfactant addition. Our numerical model is extensively calibrated with computed tomography (CT) scans and pressure drop data during coreflood experiments. Our model shows that surfactant addition into the fracturing fluid results in a better water blockage removal than fracturing water alone, because surfactant results not only in a shallower invasion depth, but also a much milder blockage within the shallower invasion depth itself. Furthermore, our model also discovers that the restoration of hydrocarbon permeability by surfactant could demonstrate a time-dependent behavior, based on the interplaying effects among IFT reduction, fracture clean-up state, and the wettability of the matrix-fracture interface. Overall, by presenting the mechanistic analysis, this study serves as a crucial step toward the optimization of surfactant formulation for fracturing fluid and EOR applications in tight reservoirs.