Numerical investigation of kerogen-fluid interactions impacting gas-water relative permeability in shale fractures

Relative permeability modifiers can selectively reduce the permeability of water while maintaining or improving the permeability of hydrocarbons. To understand the impact of fluid interactions on kerogen wettability alterations near a created hydraulic fracture, this study employed kerogen isolates from Triassic Montney shales, quantifying wettability alterations induced by hydraulic fracturing fluid, brine, and deionized water using a drop shape analyzer. An empirical model characterized time-dependent contact angles, while numerical simulations at centimeter and micrometer scales elucidated the influence of viscosity ratios and contact angle variations on flow dynamics. The results demonstrated that kerogen wettability alterations were governed by the duration of fluid interaction, leading to extended breakthrough time during gas displacing liquid processes. Moreover, higher viscosity ratios amplified this effect. Micrometer-scale models exhibited phenomenon such as liquid bridges, channels, and gas bubbles. In cases with elevated liquid-gas viscosity ratios, liquid relative permeability initially exceeded one but decreased upon complete gas displacement. Enhanced gas displacement was associated with longer contact angle change times, as well as increased initial and final contact angles. Ultimately, increased hydrophilicity led to poorer gas and water flow behaviors, characterized by lower relative permeabilities, higher residual gas saturation, and extended times to achieve residual gas saturation. This study provided crucial insights into the kerogen wettability alteration resulting from interaction with injected fluids near hydraulic or secondary fractures.