ABSTRACT:

The interaction between Hydraulic Fractures (HF) and Preexisting Discontinuities (PD, like bedding planes and natural fractures, is affected by the coefficient of friction of the PD, the state of stress around the interacting fractures' tips, and the angle between the approaching HF and the PD. Recent formulations (Kresse et. al, 2013; Chuprakov and Prioul, 2016), also consider the effect of flow rate, fluid viscosity, and PD permeability in the crossing interaction. In this study, a series of permeability tests on cylindrical Opalinus Clayshale specimens were conducted in a triaxial pressure cell. The specimen of 1.5 in diameter and 3 in height includes a throughgoing longitudinal cut, representing the PD. Different confining pressure (CF) and flow rate (FR) conditions were tested for the same fluid (constant fluid viscosity) and temperature. The results obtained are comparable with other authors, with the Opalinus clayshale showing a higher fracture conductivity than Barnett shale (Zhang et al., 2013)), and Fayetteville shale (Jansen et al., 2015).

1. INTRODUCTION

Hydraulic permeability of rock discontinuities is widely investigated in geotechnical engineering and geomechanics. This is mainly due to the influence of mechanical discontinuities, such as fractures and faults, on the permeability of rock formations. Permeability is a critical parameter in the evaluation of numerous geotechnical and environmental aspects, including slope stability, underground fluid flow, and storage, exploitation of hydrocarbon resources, etc. Preexisting discontinuities (PD) act as preferential channels for flow, and the characterization of their permeability is vital to accurately model flow. Furthermore, in the context of geological storage and carbon sequestration, the permeability of discontinuities is essential to evaluate the long-term integrity of the host formations. Many authors have studied the effect of permeability of discontinuities. For instance: Carlsson and Olsson (1993) analyzed the increase in conductivity in fractures due to shear displacement. Makurat (1996) showed that the permeability of natural fractures is affected, among other factors, by tortuosity, roughness, and wall strength.

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