MICRO-PIV STUDY OF MULTIPHASE FLOW OF WATER AND SUPERCRITICAL CO2 IN 2D HETEROGENEOUS POROUS MICROMODELS AT RESERVOIR CONDITIONS

Multiphase flow of water and supercritical CO₂ in porous media is central to the geologic sequestration of CO₂ within saline aquifers. The coupled flow dynamics of CO₂ and brine in geologic media must be better understood, particularly at the pore scale, as pore-scale processes represent a critical component of accurately predicting large-scale migration of injected CO₂.

To this end, the pore-scale flow interactions of water and liquid/supercritical CO₂ are being quantified experimentally in 2D heterogeneous porous micromodels at reservoir-relevant conditions (i.e., 80 bar, 20°C), in an attempt to accurately mimics the process of CO₂ injection into saline aquifers. The micromodels used in these experiments were fabricated from silicon, with the porous matrix formed from the reprint of the pore structure of real sandstone. Fluorescent microscopy and the micro-PIV method are employed to simultaneously measure the spatially-resolved instantaneous water velocity field and quantify the instantaneous spatial configuration of both phases. The initial results provide a clear picture of the flow physics during the migration of the CO₂ front, the evolution of individual menisci and the growth of dendritic structures, so-called fingers. During the CO₂ infiltration process, CO₂ suddenly breaks through the resident water, forming fingers which grow in directions both along and normal to the bulk pressure gradient, and even against the bulk pressure gradient, indicative of capillary fingering. The complex phase configuration highlights the importance of local pressure gradients in CO₂ front migration. These experimental data will be directly compared with available numerical simulations from a collaborative effort, yielding valuable insight into flow processes at the pore scale in natural rock.

The focus of current efforts are to construct similar heterogeneous micromodels with varying wettability to study the impact of grain wettability on the observed fingering physics upon injection of CO₂ and concomitant displacement of the resident water.