GEOLOGICAL FORMATIONS FOR FLUID STORAGE AND EXTRACTION: PETROPHYSICAL STUDIES

A range of different kinds of subsurface lithologies, such as sandstones and carbonates in deep saline aquifers & depleted oil and gas reservoirs, granites in geothermal reservoirs, organic-rich shale, claystones, basalt, and salt rock can be candidates for fluid storage and extraction in the emerging fields of energy geosciences in the context of carbon neutrality. Fluid storage involves scenarios of short-term gas (hydrogen, compressed air) storage, permanent CO₂ geological storage in a broad spectrum of carbon capture, utilization, and storage, and millions of years repository for storing high-level nuclear wastes. These systems commonly need effective reservoirs (sandstones, carbonates) for large-volume storage (e.g., sufficient effective porosity and permeability) and impermeable cap rock (mudrocks and salt rock) for containment (e.g., limited permeability, diffusivity, and tortuosity). This work studies a range of representative rock samples, such as Berea sandstone, Guelph dolomite, Indiana limestone, Woodford claystone, Haynesville Shale, Texas basalt, Sierra white granite, and Himalayan salt rock, to investigate the important petrophysical attributes (properties of rocks and fluids, as well as fluid-rock interactions) in terms of vast lithological difference, as well as different methodologies and sample scale effects of quantification. There is a particular focus on how microscopic pore structure (especially pore connectivity) influences macroscopic fluid flow and chemical transport, and hence the expected performance of these geological formations in either storing or extracting various fluids. In conjuction with a set of complementary approaches for pore structure characterization (such as small angle neutron/X-ray scattering), this work utilizes several custom designed apparatuses (e.g., gas diffusion) to provide the essential information of CO₂ diffusivity and tortuosity of natural rocks, in the presence of other gases (CH₄, H₂, and O₂).