Experimental Investigation on the Pressure Propagation Mechanism of Tight Reservoirs

Abstract

Low permeability tight sandstone reservoirs have a high filtrational resistance and a very low fluid flow rate. As a result, the propagation speed of the formation pressure is low and fluid flow behaves as a non-Darcy flow, which typically displays a highly non-linear behavior. In this paper, the characteristics and mechanism of pressure propagation in this kind of reservoir are revealed through a laboratory pressure propagation experiment and through data from an actual tight reservoir development. The main performance mechanism is as follows: A new pressure cage concept is proposed based on the pressure variation characteristics of the laboratory experiments. There are two methods of energy propagation in the actual water injection process: one is that energy is transmitted to the deep reservoir by the fluid flowing through the reservoir, and the other is that energy is transmitted by the elasticity of the reservoir. For one injection well model and one production well model, the pressure distribution curve between the injection and production wells, as calculated by the theoretical method, has three section types, and they show an oblique “S” shape with a straight middle section. However, the actual pressure distribution curve is nonlinear, with an obvious pressure advance at the front. After the injection pressure increases to a certain level, the curve shape is an oblique and reversed “S” shape. Based on the research, this paper explains the deep-seated reasons for the difference in pressure distribution and proposes that it is an effective way to develop low permeability tight reservoirs using the water injection supplement energy method.