Non-linear fluid flow through rough-walled fractures: The role of shear displacement on the critical Reynolds number

Abstract

This paper experimentally examines the role of shear slip on the variation of critical Reynolds number and non-linearity of fluid flow through rough-walled rock fractures. First, a criterion was developed by comprehensive using of Forchheimer's law to quantify the onset of non-linearity of fluid flow. Hydromechanical laboratory experiments were performed on different initially closely mated rock fractures undergoing shear sliding to evaluate effects of mechanical displacements on non-linear flow. At each shear sliding step, several high-precision water flow tests with different hydraulic gradients were carried out and the critical Reynolds number was determined based on the developed criterion. The results show that; (i) the quadratic polynomial regression in the form of the Forchheimer's law provides a good accuracy, (ii) during shear sliding, the coefficients of viscous and inertial pressure drop experiences about four and seven orders of magnitude reduction, respectively, and (iii) the critical Reynolds number varies from 0.001 to 25 and experiences about four orders of magnitude enlarging by increasing shear displacement from zero to 20 mm.