Impact of complicated pore shape on permeability stress-sensitivity analyzed by machine learning method

Permeability stress-sensitivity plays an important role in production estimation for unconventional oil/gas reservoirs. After hydraulic fracturing and long-term production, three principal stresses have different alteration magnitudes and often re-orientated.Our former study analyzing about the permeability stress-sensitivity of ellipse pore points out that impacts of value and orientation alterations of stress on permeability alteration are important. Through the elasticity theory, area change for ellipse pore can be theoretically obtained but ones for pores with complicated shapes cannot be obtained. In this study, for pores with shapes, Based on 2D solid mechanics model, solutions of area change under different stress states were calculated by the finite element method and over 835 sets of numerical simulation data were obtained. Based on porosity definition and relationship between permeability and porosity, permeability alternations caused by stress alteration were obtained. The correlations between permeability alternation and several variables were analyzed and key variables significantly affecting permeability were found out. Based on the machine learning method, the stress-dependent permeability model was built and the sensitivity study was conducted to investigate impacts of pore geometry, principle stress value and orientation on permeability evolution.It is suggested that pore geometry characteristics and stress orientation have significant roles on permeability stress-sensitivity.