Effect of dynamic pseudo threshold pressure gradient on well production performance in low-permeability and tight oil reservoirs

Abstract

Pseudo threshold pressure gradient (PTPG) is a significant parameter that characterizes fluid flow in low permeability and tight reservoirs, which would illustrate pressure derivative curves anomaly caused by low-velocity non-Darcy flow. During the development of low-permeability and tight reservoirs, PTPG is a dynamic parameter influenced by effective stress. A series of core flooding experiments have been conducted in this paper to conclude the relationship between effective stress and PTPG with the unique experimental method. In the experiment, the precision of pressure measurement is greatly improved by a novel device and the influence of the core-end effect and the defects of the core holder on the experimental results is eliminated. The results show that PTPG increase along with the increase of effective stress. Based on the conclusion, a dynamic PTPG model is established, and the corresponding parameters are derived by fitting the experimental data. The well performance of a vertical well estimated by this model shows the production rate and recovery factor of non-Darcy flow considering dynamic PTPG are smaller than that of Darcy flow but larger than that of conventional non-Darcy flow. The recovery factor of non-Darcy flow considering dynamic PTPG is 21.2% higher than that of conventional non-Darcy flow when the production time is 800 days. The production rate and recovery factor curves of different overburden pressure show that the higher the overburden pressure is, the worse the productivity of the well is. The recovery factor at an overburden pressure of 50 MPa is 11.1% lower than that at an overburden pressure of 30 MPa.