Gas-water relative permeability model for tight sandstone gas reservoirs

The pores in tight sandstone gas reservoir are mostly in microscale, and the gas water two-phase flow behavior through those pores is considerably complicated, thus, how to establish a reliable relative permeability model is the urgent problem to be solved. Based on the single fluid continuity equation of the microtube, second-order slip model and the fractal scaling theory, the gas-water relative permeability model of tight sandstone gas reservoir is established. The model considers the gas slippage effect, the pore throat structure and the water saturation distribution. The reliability is validated by a variety of published experimental data of gas-water relative permeability. The results show that: 1) The established model can be reasonably adopted to describe the fluid flow behavior in the tight sandstone reservoir with microscale pores. 2) The increase of pressure and water saturation will reduce the effect of slippage effect on the relative permeability of gas phase. When the pressure is less than 1 MPa, the gas relative permeability is extremely sensitive to the pressure. The impact of temperature on the gas relative permeability is limited and can be neglected. 3) A higher fractal dimension of pore size distribution is beneficial to the relative permeability of gas phase, but it has a negative impact of the relative permeability of water phase. Similarly, a higher fractal dimension of tortuosity results in a higher gas phase relative permeability but a little lower water relative permeability.