Influence of stress sensitivity on microscopic pore structure and fluid flow in porous media

Abstract

At present, large quantities of experiments related to stress sensitivities on the macroscale have been conducted. Pore structure is complicated, especially in unconventional reservoirs of tight sandstone. As a result, stress sensitivity has a great influence on changing the pore space. This is of great significance for enhancing oil recovery to systematically study the stress sensitivity at the pore scale. In this paper, based on CT scanning technology, which can capture the real pore space characteristics of the core samples, and combined with a digital core and pore network model, the relationships between the effective stress and the pore structure are obtained. First, the theory and method of constructing the digital core and extracting the pore network model according to CT scanning are introduced. The 3D core image could be obtained after CT scanning, and the digital core is established after filtering and segmentation. The rock structure characteristics are obtained from analyzing the geometry-topology structure of the extracted pore network model, and the fluid flow analysis is conducted by numerical flow simulation. Second, the stress sensitivity experiments and analysis are conducted. Stress sensitivity experiments are performed in the carbon fiber core holder, and the core is scanned under a series of pressures. Digital cores and pore network models under a series of pressures are obtained, and the corresponding pore structure characteristics and fluid flow laws are analyzed. Last, these methods are employed in middle-high permeability sandstone and tight sandstone. The stress sensitivities of these sandstones are achieved and compared. In this paper, the stress sensitivity evaluation method at pore-scale is developed, which has the practical application of oilfield development.