Determination of the aperture distribution of rough-walled rock fractures with the non-toxic Yield Stress fluids porosimetry method

Abstract

Fractures in geological formations constitute high-conductivity conduits which potentially act as preferential paths during fluid injection in soil remediation and reservoir engineering operations. Recently, the measurement of the pressure drop under different flow rates during the flow of yield stress fluids in porous media has been proposed as the basis for an environmentally friendly method to characterize the Pore Size Distribution. However, the Yield Stress fluids porosimetry Method (YSM) has still not been extended to the characterization of the hydraulic aperture distribution of rough-walled rock fractures. The potential interest of such an extension is intense, considering that the distinct characteristics of rock fractures vs the matrix represent a burden to other traditional porosimetry techniques. In the particular case of X-ray microtomography, time-consuming calibration is often needed, and serious difficulties arise due to beam hardening and reconstruction artifacts. The specific objective of the present investigation is to adapt YSM to the characterization of rough-walled rock fractures. For this purpose, the results of laboratory experiments in which a yield stress fluid was injected through two natural rock fractures were exploited, and the YSM model and algorithm was adapted to the particular topological and geometrical features of flows in fractures. Moreover, numerical experiments were performed at the scale of a single 2D channel with variable aperture to identify the dimension characterized by YSM and decipher the yielding behaviour of the fluids. The present findings show that YSM can be successfully used to characterize the distribution of hydraulic apertures of the flow channels in rough-walled rock fractures. Furthermore, the numerical results revealed that the plug of stagnant fluid is located in the central part of these flow channels and breaks close to the constrictions, forming islands of unyielded fluid.