Permeability Stress Sensitivity Study Of Tight Reservoir Rocks

During the continuous production of tight oil and gas reservoirs,the formation pressure decreases and the pore and micro cracks in reservoirs becomes deformed,the effective stress showed obvious nonlinear.The previous linear effective stress theory cannot objectively describe permeability variation with the pore pressure and evaluate effects of stress sensitivity on the productivity of tight reservoirs during mining process.Therefore,this article carried experiments on tight rocks to study permeability effective stress and stress sensitivity through the investigation of effective stress theory and experimental research at home and abroad.The main work done and the knowledge gained are as follows:(1)The theoretical model of effective stress coefficient is deduced,and the influence of clay and crack on the effective stress coefficient of rock is analyzed theoretically based on parameter analysis;(2)The basic physical properties of rock samples were tested,and the microscopic characteristics were analyzed by scanning electron microscope,cast slice test,X diffraction test and mercury intrusion test;(3)The stress sensitivity experiments are carried out with N2 and formation water respectively on 2 pieces of natural fracture rock and 3 artificial fracture rock as well as 5 matrix rock to study the influences of pore fluid type and fracture on permeability stress sensitivity coefficient;(4)The response surface secant method is used to calculate and analyse law for the effective stress coefficient and variation range;(5)The relationship between permeability and effective stress is studied by theoretical model and empirical formula respectively,the expressions of stress sensitivity coefficients are obtained and their physical meanings are defined;(6)The analytical solution for well productivity formula is derived and verified by numerical simulation,which provides a evaluation method for stress sensitivity of reservoir based on loss of productivity.This study established a set of methods to obtain stress coefficient method,based on the definition and data analysis methods of the effective stress.This article further deepened the understanding of the variation of effective stress through the study on the permeability of the effective stress,and the influences of clay,pore fluid type and fracture of rock on the effective stress coefficient was analysed by combination of microscopic characteristics and effective stress experiment results of rocks.