Constraining fluid-rock interactions during eogenetic karst and their impacts on carbonate reservoirs: Insights from reactive transport modeling.

Eogenetic karst has been regarded as a dominant origin of hydrocarbon reservoirs, whereas quantifying the fluid-rock interactions and their impacts on porosity evolution during the palaeokarst process remain persistent challenges that limit the accuracy of reservoir quality prediction. This study investigates the dissolution of carbonate rocks with potential controlling factors by reactive transport modeling that couples fluid flow, mineral reactions and porosity changes in a one-dimensional vadose meteoric water-rock system. Simulation results of base case scenario and sensitivity analyses show that the duration of subaerial exposure and recharge capacity of rainwater significantly determine the karst-affected depth and porosity increment. The amount of calcite dissolution is also affected by a downward decrease in calcite solubility (temperature-dependent) and the enrichment of Ca2+ and HCO 3 − in the lower part. The atmospheric carbon dioxide concentration has a minor impact on the vertical extent of karst, while it facilitates the dissolution rate under high pCO 2 conditions. The influence of atmospheric pCO 2 variation over geological time on the porosity increment was reconstructed under hydrogeological conditions of the base case scenario (exposure time = 130 ka; rainfall = 628 mm/a). The differences in the dissolution rates and extent of karst between limestone and dolostone can be interpreted as the results of different rate-determining reaction mechanisms, i.e., thermodynamically controlled calcite and kinetically controlled dolomite. • Key factors affecting eogenetic karst are semi-quantitatively evaluated using reactive transport modeling. • The influence of atmospheric pCO 2 variation over geological time on the porosity increment is reconstructed. • Different rate-determining reaction mechanisms result in higher dissolution rate of calcite than dolomite. [ABSTRACT FROM AUTHOR]