Modelling the Impacts of Water Blocking During Gas Production fromCompressible Shales

摘要

The aim of this work is to study shale gas production subject to water blocking in compressible shale. Waterblocking is a capillary pressure end-effect causing the wetting phase (e.g. water) to accumulate near thetransition from a porous medium to an open medium; in this context, a transition from shale matrix to ahydraulic fracture. Shale is considered a tight porous medium with ultralow permeability, and hydraulicfracturing is essential to obtain economical production. Water is frequently used as a fracturing fluid, but itsaccumulation at the matrix end-face reduces the gas mobility and can lead to rapid decline of gas productionrate. The tight nature of the shale as a porous medium also introduces non-standard flow and storagemechanisms. This work develops a mathematical model that accounts for apparent permeability,compressibility of gas and shale, gas adsorption, Forchheimer gas flow, and multiphase flow parameterslike relative permeability and capillary pressure, which depend on wettability. The behavior of the modelat steady state production is explored to understand the impact of the various mechanisms.