The elastic anisotropy and mechanical behaviour of the Whitby Mudstone

Abstract

Mudstones play an important role in hydrocarbon exploration and production, carbon capture and storage, and nuclear waste disposal. The high concentration of clay minerals contribute to the high intrinsic anisotropy (e.g., velocity, strength, permeability, and resistivity changes with direction) of mudstones. This high anisotropy complicates, among other things, seismic interpretation for hydrocarbon exploration and production, as well as predictions on the mechanical behaviour of these clayrich rocks. Mudstones are also characterized by a low-permeability matrix, which makes it difficult for fluids to flow through the rock. This impermeable character of mudstones makes them a potential natural seal for long-term CO2 storage and a potential host rock for nuclear waste disposal. For hydrocarbon production, open fractures are needed to enhance the productivity of oil and gas reservoirs, whereas the presence of such fractures can result in unwanted leakage of CO2 or nuclear waste in the subsurface. Fracture formation depends on, among other things, the mechanical properties of the mudstone. It is thus important to understand the elastic anisotropy and mechanical properties of mudstones for successful hydrocarbon exploration and production, and to safely store CO2 and radioactive waste in the subsurface. Although mudstones are important in the energy sector, the understanding of their elastic anisotropy and deformation behaviour under various physical conditions is limited, due to their complex character and the lack of laboratory experiments performed on well-preserved samples.