Investigating Aperture-Based Stress-Dependent Permeability and Capillary Pressure in Rock Fractures

Abstract

Understanding multi-phase fluid flow behavior in fractured porous media is crucial for developing fractured hydrocarbon reservoirs, implementing hydraulic fracturing, and predicting potential leakage in gas and CO₂ storage. The goal of this research is to investigate stress-dependent permeability and capillary pressure in rock fractures. Laboratory measurements of fracture aperture distributions have been made using CT scanning under various conditions of effective stress. By applying the stress-dependent aperture data, numerical simulation is employed to model the change of permeability and capillary pressure in the rock fracture as a function of the effective stress.

The stress-dependent aperture distribution data demonstrates that increasing stress results in two effects: (1); the mean aperture will decrease; (2); the variance of aperture distribution will increase. Experimental results show that permeability will drop by 73% when effective stress increases from 0.34MPa to 22.06MPa. As the variance of aperture distribution increases with stress, the plateau area of the capillary pressure curve tends to grow steeper, indicating that capillary behavior changes from more fracture-like to more porous media-like. The impacts of mean and variance of aperture distributions on permeability and capillary pressure are separately analyzed. The mean aperture decrease will reduce permeability and increase entry pressure. The variance increase will reduce permeability, the pore size distribution index and entry pressure. By analyzing the stress-dependent mean and variance of aperture distributions, this paper provides a more straightforward way for estimating stress-dependent permeability and capillary pressure in rock fractures.