Numerical and Laboratory Studies of Fluid Transport Between Two Matted Rough Surfaces and Realistic Assessment of Permeability of Fractured Medium

摘要

This paper presents an innovative approach to estimate fracture permeability of rocks under different confining pressures and shear displacements by taking into account of fracture surface asperities. The topography of the fracture surface is imaged by surface scanning to determine distribution of surface asperities and their heights. Fluid flow inside the fracture is simulated using the Reynolds equation. In simulating fluid flow interaction between the asperities of the two mating fracture surfaces under different stress conditions is considered. Permeability of the fracture is then calculated based on the fluid velocity distribution between the fracture surfaces. This methodology has allowed us to study preferential flow paths in the fracture (flow channelling) due to change in aperture caused by the confining pressure. The numerical results are verified against results obtained from laboratory experiments using naturally fractured granitic rock samples. The results of this study have shown that the proposed methodology can estimate the fracture permeability accurately by taking into account of the effect of deformation of surface asperities at different confining pressures. Results of this study will shed some light to provide an improved understanding of causes of high impedance between injector and producer and allow development of new stimulation techniques for increasing production rate from enhanced geothermal systems.