An integrated model is developed to study the skin damage and liquid cleanup of hydraulically fractured wells during post-fracture production. The adverse effects of an injected liquid phase present in the invaded region adjacent to the fracture are simulated by the two-phase and threedimensional flow equations for gas and water in formation, fracture and damaged zone. A phenomenological model simulating the effects of clay swelling and migration of fines leading to skin in the liquid invaded region is incorporated in the study.
Simulation of liquid cleanup is accomplished by first considering the injection of fracturing fluid to study the extent of invaded region and the degree of permeability reduction. This is followed by simulation of liquid recovery and gas production under altered reservoir conditions.
It is found that the mathematical modeling of fluid injection and subsequent cleanup requires formulation of non-linear and coupled model equations, prudent numerical schemes, implementation of refined grids and curvilinear coordinates, and versatile solution methods. The model has been applied to typical field cases, and simulation results indicate that factors such as permeability alteration in the damaged zone and gas relative permeability in presence of a liquid phase must be considered in designing a successful hydraulic fracturing operation.