Pore-scale investigation of bottom water invasion dynamics in carbonate gas reservoirs with different interlayer distributions

Abstract

During the development of carbonate reservoirs, the risk of bottom water invasion is a frequent concern. Pore-scale simulation methods are commonly acknowledged as effective tools for investigating the dynamics involved in water invasion mechanisms. Despite extensive research on gas-water two-phase flow, few studies have investigated reservoirs with interlayers, which can remarkably affect assessments of water invasion. Three models were designed to study the effects of different interlayer distributions on flow behavior. A mathematical model based on the volume of fluid (VOF) method was employed to describe variations in water saturation. The four primary influencing factors (interlayer distribution, gravity, pressure difference, and wettability) were studied based on simulations. The accuracy of the model was validated through comparisons with microfluidic visualization experiments. Compared to the model without interlayers, the models with semi-permeable and semi-sealed interlayers reduced the risk of water invasion, resulting in slower upward water saturation rates and delayed water breakthrough times. Neglecting gravity would introduce errors of up to 5.6% in water saturation and 24.2% in water breakthrough time for the models with interlayers. Controlling the pressure difference within 1.5 MPa/100 m would effectively reduce the produced water-gas ratio and delay the water breakthrough time. The water invasion behavior in the models with interlayers was highly sensitive to contact angles in the range of 50°–60°, while its effect on the model without interlayers was relatively small. Field-scale water invasion dynamics with examples from the Yuanba (YB) gas field in the Sichuan Basin, China, were consistent with the pore-scale simulation results. This work provides fundamental support for and valuable insights into the development of similar gas reservoirs, offering a strong foundation for future endeavors in this field.