Chemically Induced Evolution of Morphological and Connectivity Characteristics of Pore Space of Complex Carbonate Rock via Digital Core Analysis

Abstract

We study the impact of reactive flow on a complex carbonate rock whose pore space was resolved by X-ray μ-CT. A small core plug was imaged in the original and chemically altered states. The morphology of the resolved pore space was quantified using various approaches, such as sample-spanning cluster analysis, capillary drainage transform (CDT), and Minkowski functionals. In particular, we carefully evaluated the changes in macropore connectivity by calculating the fraction of percolated cluster, the Euler characteristic of macroporous phase, and the critical pore diameter in pre- and post-alteration states. We observed that the reactive flow mainly affected larger pores in the macropore region of the sample. More importantly, a huge increase in macropore connectivity, as indicated majorly by the CDT measurements and the Euler characteristic, was observed such that the poorly connected original macropore phase was converted to well-connected ones after the reactive flow. In addition, the increases in the macropore surface area and integral mean curvature indicated that the oomoldic and interooidal pores of the rock were dominantly enlarged by the reactive fluid. Based on direct numerical simulations on the main flow paths (i.e., the macro-connected pore phase), strong correlations were found between changes in transport properties and the evolution of connectivity and length scales of the macropore phase, such that simple power-law models could be used to predict with acceptable accuracy. This suggests that the evolution of transport properties of the rock was mainly controlled by the changes in the macro-connected porosity and the critical pore diameter.