A spatially correlated heterogeneous anisotropic model for simulation of gas flow in Callovo-Oxfordian claystone

A long-term gas injection test on Callovo-Oxfordian claystone (COx) has been performed by the British Geological Survey (BGS), and it is simulated with a coupled hydro-mechanical model. The approach is implemented in the software CODE_BRIGHT, considering a spatially correlated heterogeneous field of initial porosity. The correlation length is assumed to change in different directions. An important feature of this approach is that material properties such as elastic modulus, diffusivity and intrinsic permeability are functions of porosity, leading to the emergence of heterogeneity and anisotropy of these properties. An embedded fracture model is adopted to describe significant changes of intrinsic permeability due to the opening of apertures, caused by gas pressure-induced deformations. Sensitivity analyses have been conducted with respect to parameters in the embedded fracture model, guard ring volume, diffusivity and the sample orientation to understand gas migration mechanisms through COx. The results show that the adopted approach can capture the observations of the experiment.