Qualitative Dissolution Modeling of Etch‐Pit Formation on the K‐Feldspar Surface Through Phase‐Field Approach

Abstract

AbstractReservoir quality of sandstones can be controlled by the dissolution of minerals such as K‐feldspar. The present work investigates the impact of dissolution of K‐feldspar (Orthoclase) on the resulting porosity and permeability of sandstones using a thermodynamically consistent multiphase‐field model. Two novel aspects of this research are: (a) identification and calibration of interfacial surface energy and kinetics related model parameters based on existing literature, to account for the formation and growth of diamond‐shaped etch‐pits during dissolution, and (b) the workflow for three‐dimensional modeling of dissolution at sub‐micrometer scale within individual feldspar grains, followed by up‐scaling the phenomenon to a multigrain pack analogous to sandstone. The simulated dissolution, when visualized in the relevant planes, show clear similarities with microphotographs of natural samples and previous numerical works, in terms of facet‐formation and merging of the etch‐pit morphologies. For the computation of permeability, computational fluid dynamics analysis was performed for grain packs at different stages of dissolution. Finally, the generated data‐sets were analyzed to study the impact of rock properties including a fraction of feldspar grains and their crystallographic orientation on the porosity, permeability and their correlations, for sandstones undergoing K‐feldspar dissolution. At the same porosity, sandstones containing a greater proportion of K‐feldspar grains are expected to have greater permeabilities. The devised workflow for model calibration and up‐scaling complimented by the innovative post‐processing and visualization techniques can be adapted to study dissolution of other minerals in different rocks.