Quantifying the flow dynamics of supercritical CO₂–water displacement in a 2D porous micromodel using fluorescent microscopy and microscopic PIV

The multi-phase flow of liquid/supercritical CO₂ and water (non-wetting and wetting phases, respectively) in a two-dimensional silicon micromodel was investigated at reservoir conditions (80 bar, 24 °C and 40 °C). The fluorescent microscopy and microscopic particle image velocimetry (micro-PIV) techniques were combined to quantify the flow dynamics associated with displacement of water by CO₂ (drainage) in the porous matrix. To this end, water was seeded with fluorescent tracer particles, CO₂ was tagged with a fluorescent dye and each phase was imaged independently using spectral separation in conjunction with microscopic imaging. This approach allowed simultaneous measurement of the spatially-resolved instantaneous velocity field in the water and quantification of the spatial configuration of the two fluid phases. The results, acquired with sufficient time resolution to follow the dynamic progression of both phases, provide a comprehensive picture of the flow physics during the migration of the CO₂ front, the temporal evolution of individual menisci, and the growth of fingers within the porous microstructure. During that growth process, velocity jumps 20–25 times larger in magnitude than the bulk velocity were measured in the water phase and these bursts of water flow occurred both in-line with and against the bulk flow direction. These unsteady velocity events support the notion of pressure bursts and Haines jumps during pore drainage events as previously reported in the literature [1–3]. After passage of the CO₂ front, shear-induced flow was detected in the trapped water ganglia in the form of circulation zones near the CO₂–water interfaces as well as in the thin water films wetting the surfaces of the silicon micromodel. To our knowledge, the results presented herein represent the first quantitative spatially and temporally resolved velocity-field measurements at high pressure for water displacement by liquid/supercritical CO₂ injection in a porous micromodel.