Simulation of Gas-water Two-phase Micro-scale Flow in Tight Sandstone Reservoir

Abstract

China is rich in tight gas reservoir resources, but the production of tight gas wells is greatly affected by water production. In order to further explore the law of tight gas two-phase flow and improve the recovery ratio of a single well. Based on the Lattice-Boltzmann method (LBM), this paper establishes a gas-water two-phase Lattice-Boltzmann model of tight sandstone reservoir, simulates the micro-scale flow of tight sandstone reservoir, clarifies the occurrence law of gas-water in Production layer, and studies the micro-scale flow mechanism of the tight gas reservoir. The results show that the irreducible water of tight sandstone reservoirs mainly has four modes of occurrence: blocking water, blind pore water, dead-end pore water and adsorbed liquid film. Residual gas mainly exists in rock pore throats in three forms: dead-end pore gas, narrow-throat pore gas and closed gas. At the initial stage of two-phase infiltration flow, the liquid phase exists in the form of an adsorption liquid film, which affects the gas phase flow by reducing the flow area of the gas phase. In the middle and late stages, the liquid phase mainly blocks the throat in the form of droplets, thus affecting the gas phase flow. The tight sandstone reservoir is affected by capillary force, liquid-solid viscosity, pore throat structure and other reasons, which are easy to cause water lock damage and seriously reduce the single well production and recovery ratio of tight gas reservoirs. Fracturing is an effective means to improve the overall seepage capacity of tight reservoir fluid. With the increase of fracture width, continuous liquid films on both sides of the fracture restrict the cross-flow between fracture and matrix, further strengthening the water lock damage of the matrix.