Evolution of porosity and permeability during carbonate precipitation

Detailed characterization of how pore space is structurally modified during carbonate precipitation and dissolution can improve our understanding of how diagenesis impacts reservoir properties. Such knowledge is crucial for accurate estimation of rock permeability for many applications such as enhanced oil recovery, CO₂ sequestration, and groundwater remediation. In this study, we conducted controlled laboratory experiment and pore-scale numerical simulations to investigate the evolution of permeability of Bahamian oolitic sand during carbonate precipitation. We used packed natural ooids as the sample, and the calcium carbonate precipitation was realized by flowing CaCO₃ oversaturated fluids through the sample with different flow rate. Geochemistry conditions (carbonate mass loss, alkalinity, pH, and Ca²⁺ concentration) were monitored in outflow and geophysical measurements (spectral induced polarization) were taken along the column. The permeability k of the sample during the test was measured using the constant head method. The experimental data are compared with the simulated results to provide insights into the evolution of petrophysical properties during calcite precipitation and dissolution. It is revealed that the k evolution pattern during precipitation is closely related to the flow condition. At high flow rate, k varies roughly as a power function of porosity ϕ with a nearly-contact exponent. At low flow rate, however, k and ϕ do not follow a power relation. The different macroscopic responses can be explained by their relevant pore-scale precipitation patterns as revealed by the numerical simulation.