Pore-scale Evaluation of Immiscible Fluid Characteristics and Displacements: Comparison Between Ambient- and Supercritical-Condition Experimental Studies

Abstract:

The transport of immiscible fluids within porous media is a topic of great importance for a wide range of subsurface processes; e.g. oil recovery, geologic sequestration of CO₂, gas-water mass transfer in the vadose zone, and remediation of non-aqueous phase liquids (NAPLs) from groundwater. In particular, the trapping and mobilization of nonwetting phase fluids (e.g. oil, CO₂, gas, or NAPL in water-wet media) is of significant concern; and has been well documented to be a function of both wetting and nonwetting fluid properties, morphological characteristics of the porous medium, and system history. However, generalization of empirical trends and results for application between different fluid-fluid-medium systems requires careful consideration and characterization of the relevant system properties.

We present a comprehensive and cohesive description of nonwetting phase behaviour as observed via a suite of three dimensional x-ray microtomography imaging experiments investigating immiscible fluid flow, trapping, and interfacial interactions of wetting (brine) and nonwetting (air, oil, and supercritical CO₂) phase in sandstones and synthetic media. Microtomographic images, acquired for drainage and imbibition flow processes, allow for precise and extensive characterization of nonwetting phase fluid saturation, topology, and connectivity; imaging results are paired with externally measured capillary pressure data to provide a comprehensive description of fluid states. Fluid flow and nonwetting phase trapping behaviour is investigated as a function of system history, morphological metrics of the geologic media, and nonwetting phase fluid characteristics; and particular emphasis is devoted to the differences between ambient condition (air-brine) and reservoir condition (supercritical CO₂-brine) studies.

Preliminary results provide insight into the applicability of using ambient condition experiments to explore reservoir condition processes, and also elucidate the underlying physics of trapping and mobilization of nonwetting phase fluids.