Discussion on Factors Affecting Threshold Pressure Gradient in Tight Sandstone Reservoirs

The threshold pressure gradient is a key parameter in studying the flow mechanism in low-permeability oil and gas reservoirs, which controls flow characteristics and influences oil recovery. The threshold pressure gradient can reflect the exploitation difficulty for some oilfield to a certain extent. A clear understanding of the factors affecting the threshold pressure gradient is helpful for oilfield development and formulation of later adjustment plans. Referencing the nonlinear flow mechanism in the low permeability reservoirs, a fractal model of threshold pressure gradient considering the microscale effect was established by means of microscopic flow analysis. The new model shows that the threshold pressure gradient is a comprehensive embodiment of porosity, fractal dimension, permeability, maximum connected pore throat radius and ultimate shear stress, and also shows that, in low-permeability reservoirs, the threshold pressure is the result of the combined action of heterogeneity and fluid non-Newtonian properties. The study analyzes the main factors affecting the threshold pressure gradient from a microscopic perspective, and theoretically deepens the influence of microscopic heterogeneity on the nonlinear flow mechanism in low permeability reservoirs. The parameters involved in the new model are simple and easy to obtain, which is convenient for practical application in oil fields.