Determination of the Influence of Stress, Time and Bedding Orientation on the Evolution of Contact Area and Stress Distribution for Fractures in the Opalinus Clay Shale

Abstract

Humanity is facing one of the largest challenges it has come up against in its lifetime, climate change. Emission of greenhouse gasses being the largest contributor to global warming, we need to change our way of living, producing energy and transporting products all over the planet. Emission of greenhouse gasses needs to be kept at a minimum and social change only will probably not be enough. On the short term the so called techno-fixes, where technology comes in play, can help us taking a step towards reaching our mutual goal of reducing CO2 emissions. One of the most promising techno-fixes in play is Carbon Capture Storage (CCS) where CO2 is captured at the source and is geologically stored in empty reservoirs or aquifers where it can be contained for geological timescales. Of course, the storage of CO2 comes with certain risks as parts of this method are still unknown, such as the leakage potential of the in situ caprock. In this study the aim was to obtain empirical relationships for contact area and stress distribution with varying bedding orientation, stress and time for fractures in clayey caprock, in this case the Opalinus Clay shale. By performing compressibility tests with varying bedding orientations, stress and time, using pressure sensitive paper with different stress thresholds, it was observed that; 1. Intact compressibility tests show an increasing matrix compressibility with decreasing bedding orientation; 2. The effect of bedding orientation on the evolution of free space area and >15 MPa-bearing contact area with increasing applied stress shows to be neglectable and therefore empirical relationships were obtained regardless of bedding orientation; 3. Joint Roughness Coefficient (JRC) shows increasing trend with increasing bedding orientation angle (0° < θ < 90°); 4. The effect of time is visible in a logarithmic trend, where applied normal stress plays a ~1:1 role; 5. The effect of an applied initial dislocation along the fracture plane shows an increase in contact area with increasing time, which implies there is a strong self-healing property present in the Opalinus Clay shale.