Impact of Pore Structure on Stress-Dependent Behavior of Permeability for Fluid Flow Through Porous Medium

Abstract

ABSTRACT Stress-dependent behavior of permeability is an important characteristic of fluid flow through porous medium. It is widely accepted that the stress-dependent permeability behavior relates to pore volume change, but ignore the real stress distribution around pores. In this study, the coupled flow-geomechanics numerical simulation is conducted to simulate the real process of fluid flow through a real pore structure. The fluid flow inside pores is described by the laminar flow, and calculate the pore volume change by elasticity theory. Permeability is calculated by Darcy's law. The affections of pore structure on stress-dependent permeability behavior are studied and then main factors affecting this behavior are discussed. The main results show: (1) There is a dominant cross-section in the whole pore controlling the stress-dependent behavior of permeability. This dominant cross-section may be the cross-section where the flow velocity is highest along the pore. (2) The three stress components have different impacts on permeability stress-dependent behavior. The major stress component can be determined through the deformation of dominant cross-section which is the dominant one for permeability. (3) The pore geometry shape also affects stress-dependent permeability. (4) The pore's orientation also affects stress-dependent permeability behavior. INTRODUCTION Rock is a typical porous medium consisting of pores and a solid skeleton. Rock permeability is one of the most important fluid transport properties. Stress-dependent behavior of permeability significantly affects fluid flow behavior of in areas of underground storage, petroleum engineering and mining engineering. The rock permeability is determined by the connected pores and their distribution in the rock. Based on the rock mechanics theory, pore shape can cause stress concentration affecting pore deformation (Peng et al., 2021). The stress-dependent behavior of permeability results from pore deformation (Peng et al., 2022). In addition, the stress-dependent behavior of permeability is also affected by the stress variation. The in-situ stress of unconventional reservoirs varies significantly after many treatments, such as hydraulic fracturing and water flooding (Pan et al., 2012; He et al., 2020; He et al.,2020). Therefore, the stress-dependent behavior of permeability affects production behaviors of unconventional reservoirs.