Pore-Scale Exploration of Wettability Impact on Fluid Flow: Micro-CT Imaging and Relative Permeability Analysis in a Sandstone Core

Summary In recent years, advancements in microcomputed tomography (microCT) imaging technology and image processing have significantly enhanced our understanding of the internal structure of rock cores and the distribution of fluids during multiphase flow. Herein, we use microCT imaging to explore the impact of wettability on fluid flow in a sandstone rock at the pore scale in combination with relative permeability measurements. Steady-state experiments were conducted by the coinjection of decane and water into a sandstone core under different fractional flows (Fw = 0, 0.25, 0.5, 0.75, and 1) and wetting conditions. At each stabilized fractional flow, the system was imaged with microCT at a resolution of 6.7 µm under dynamic flow conditions. The sandstone core is initially tested in a clean state (i.e., water-wet condition), followed by aging in crude oil for 2 weeks at 90°C to create an aged state (i.e., oil-wet/mixed-wet condition). For the aged-state core, it was observed that the oil/water interface was dynamically changing under so-called steady-state conditions while the clean-state core provided less dynamic changes. Consequently, the aged-state core was also imaged under static conditions to capture fluid/fluid interfaces and common lines. Based on the scanned images, parameters such as contact angle, curvature, and pore occupancy were calculated, comparing differences between the clean-state and aged-state conditions. Furthermore, relative permeabilities were measured to analyze the flow characteristics at the continuum scale, providing a comprehensive understanding of pore-scale mechanisms linked to relative permeability behavior.