Pore network modelling of reactive permeability evolution during simultaneous mineral dissolution and precipitation

Abstract:

Mineral dissolution and precipitation reactions in porous media can impact the porosity and permeability in complex ways. Predicting changes in permeability is challenging where currently macroscopic empirical equations such as the Kozeny- Carman equation are often used. These equations fail to reflect the impacts of pore scale variations on permeability. This work seeks to understand the evolution of permeability in systems with varying spatial distributions of simultaneous mineral dissolution and precipitation using a MATLAB pore network model. The model consists of a network of pores on a regular cubic lattice connected by pore throats where pore and pore-throat sizes and connectivity were previously determined from analysis of X-ray CT images of a Paluxy sandstone sample. Various spatial distributions of mineral dissolution and precipitation are simulated including occurring randomly throughout the network, isolated near the inlet or outlet, and controlled by pore and pore-throat sizes. Each reaction alters respective pore and pore-throats sizes to an extent of the original radii (i.e. 15%). 1000 simulations are run for each sub-scenario and the resulting porosity and permeability values plotted and compared with the commonly used macroscopic equations. When dissolution and precipitation reactions are randomly distributed throughout the network, an overall increase in porosity occurs with little change in permeability. This scenario does not follow any of the empirical equations’ representation of porosity and permeability. In the scenarios where dissolution occurs at the inlet and precipitation at the outlet, and the respective opposite, porosity increases while permeability decreases. This is also not captured by existing porosity-permeability equations. When dissolution occurs in small pores and pore-throats and precipitation in large pores and pore-throats, porosity and permeability decrease. In the opposite system, porosity and permeability increase. Both of these scenarios are well described by the Verma-Pruess porosity-permeability equation.