A new approach to determine dynamic capillary pressure at pore scale

Abstract

Mitigating climate change requires strategies to reduce greenhouse gases from human activities. Carbon Capture and Storage (CCS) is a promising solution, provided suitable CO2 reservoirs are identified. Basalts are increasingly considered for CO2 storage due to their heterogeneous internal structure, connected vesicles, and high content of reactive minerals, which permanently sequester CO2 faster through mineral trapping than sedimentary rocks.

Immiscible two-phase flow in basalts is presumably very different compared to sedimentary rocks because of the large heterogeneity in pore sizes. However, important multi-phase flow properties such as relative permeability and capillary pressure remain poorly constrained in basalts. In this study, we use computational fluid dynamics with the Volume of Fluid (VOF) method to track the evolution of fluid-fluid interfaces. Three-dimensional X-ray micro-computed tomography (μCΤ) images of a range of pore geometries were used to simulate two-phase flow under capillary-dominated flow rates. The results were used to determine pore-scale capillary pressure (Pc) under dynamic conditions where the interfaces do not reach equilibrium. Analysis suggested that the Pc is influenced by the pore structure and size, and by the interfacial tension between the two fluid phases. This approach offers insights into preferential sites for mineralization which help predict CO2 migration and trapping.