Two-phase flow model based on 3D pore structure of geomaterials

Geomaterials normally have low pore-connectivity in underground reservoir, and the macro-scale flow simulation normally ignores the micro pore connectivity and uses macro parameters such as permeability and tortuosity to reflect the conductivity of underground reservoir. However, due to the complex pore structure and pore connectivity of geomaterials, the macro-scale method cannot reflect the micro flow mechanisms. The pore-structure model provides an effective way to reflect the micro-flow mechanisms for complex porous media since the pore geometry and pore connectivity can be included in the model itself. In this work, an equivalent pore-network model (EPNM) is established considering pore-size distribution, spatial correlation and pore-connectivity. EPNM aims at reflecting 3D pore structure of geomaterials by the equivalent hydraulic parameters, and the effectiveness is verified by permeability tests. Furthermore, a dynamic two-phase flow model is developed based on EPNM, and simulate the dynamic invasion of each phase, reflect the preferential flow in porous media, and it can provide apparent permeability, relative permeability curve, breakthrough curve for macro-scale simulation. Finally, the dynamic two-phase flow model is applied to the wetting phase trap during shale gas exploitation. The results show that the residual saturation in shale matrix is around 30%, and this residual saturation decreases significantly with the increase of the average pore coordination number.