Coreflooding without flooding: Buoyancy-based multiphase-flow core analysis for H2/CO2 storage sites

Achieving large-scale underground hydrogen storage and carbon-dioxide sequestration is central to the energy transition and climate-neutrality goals. Reliable prediction of multiphase flow in geological formations is essential for the design and safety of such systems and largely relies on accurate estimation of fluid-rock properties. However, conventional coreflooding approaches for determining permeability and relative permeability suffer from some significant drawbacks such as pressure measurement errors, end effects, gravity override and  rock damage, and yield rate-dependent relative permeability curves that are not intrinsic to the rock–fluid system. Furthermore, small-scale sub-core heterogeneity should be considered in the property estimation studies and gravity-capillary driven flow should be a focal point, as it prevails in H₂/CO₂ storage far from wells or after injection and production has been terminated, leaving the fluids to migrate due to buoyancy and capillary forces.

We present a new buoyancy-based method for estimating three-dimensional permeability (k(x,y,z)) and intrinsic relative-permeability curves (k_r) of core samples, without imposing external flow. The approach focuses on gas-water redistribution in a sealed vertical core due to gravity and capillary forces. The method inverts transient and equilibrium saturation fields obtained during the flow using imaging to recover both k(x,y,z) and k_r. Synthetic tests on numerical simulations of H₂-water flow are conducted and show that the permeability field is reconstructed with an error below 4% for almost all cases. Intrinsic k_r curves are also accurately recovered using the new method, with some errors observed for highly nonlinear curves. Parametric analyses shows that the method is generally robust and accurate, providing insight on the unique gravity-capillary driven core-flow. The new approach has numerous advantages over conventional coreflooding and could establish a pathway for more reliable characterization of geological hydrogen and CO₂ storage sites.