Numerical Simulation of Reactive Transport on Micro-CT Images

Abstract

Reactive transport is a key issue in hydrocarbon reservoirs, hydrogeological and environmental applications. A numerical model is presented to predict alteration of porous medium structure due to the dissolution mechanisms. The model includes the coupling of mass transport, chemical reactions and solid modification. It is validated by comparing reactive flow in a fracture geometry with previously published results and analytical expressions. Flow, transport, and chemical reaction are simulated directly on three-dimensional micro computed tomography images of rocks with increasing degree of heterogeneity: a sand pack, Berea sandstone, and limestone carbonate. Different regimes of transport and reaction are characterised by the dimensionless Peclet and Damkohler numbers. Dissolution patterns and geometrical evolutions of the solid phases obtained from imaging are investigated for different Peclet and Damkohler numbers and the effects of heterogeneity are included. The porosity profiles are presented in different classes of porous media after reaction. The results demonstrate different mechanisms such as uniform and face dissolution at transport- and reactive-limited regimes. The relationships between permeability and porosity are also explored. At high Peclet and Damkohler numbers, high-permeability channels are uniformly dissolved leading to significant increases in permeability. The largest changes in permeability are observed for the most heterogeneous sample, the carbonate, in all Peclet and Damkohler regimes. For low Damkohler but high Peclet numbers, a uniform dissolution occurs over the entire porous medium. The complex correlation for permeability in different porous structures is explained based on connectivity and morphological properties of the porous media obtained from porosity profiles and dissolution patterns. The exponent n in the power-law correlation between permeability and porosity is measured in different samples and our findings are consistent with experimental observations. This study helps improve the understanding of reactive flow at pore scale in porous media highlighting the interplay of Peclet and Damkohler numbers as well as the rock heterogeneity.