Numerical Simulation of Pore-Scale Fluid Mobilization during Immiscible Displacement

A significant amount of oil remains trapped in the deal-ends of a porous network during a water flooding process in an oil reservoir. A deep insight into the immiscible displacement mechanism, effect of rock and fluid properties, and dead-end geometry on the trapped oil recovery from the complex pores is required. We present numerical simulations of immiscible two-phase flow at the pore scale to understand the displacement mechanism in the complex pores (dead-ends and contraction–expansion) and parameters affecting the oil recovery. The effects of displacing phase injection velocity, viscosity ratio, wettability alteration, viscosity of trapped oil, and geometric ratio on the trapped oil recovery have been investigated. The results show that decreasing the contact angle has a marginal effect on the recovery of the trapped fluid until a critical contact angle is reached. It is observed that at smaller contact angles (water-wet condition) water displaces the oil along the dead-end walls. The simulations show that when the oil/water interface reaches the bottom of the dead-end before it reaches the rupture point at the pore throat junction, there is complete displacement. Increasing the displacing phase injection velocity significantly increases the oil recovery from dead-end pores. On the other hand, decreasing the injection velocity results in improved oil recovery from the contraction-expansion pores. The increase in the viscosity ratio (displacing phase to the displaced phase) has little impact on the oil recovery from both types of complex pores. Furthermore, it has been observed that with an increase in the dead-end depth oil recovery decreases, and the critical contact angle required for complete displacement is much lower. This study can be useful to develop the right strategies to recover trapped oil from the complex pores.