Simulation of early karstification by synergistic mixing corrosion and retrograde solubility in carbonate reservoirs

Abstract

The mixing of groundwater with varying carbon dioxide content and temperature plays a crucial role in karst evolution in carbonate reservoirs, driving both mixing corrosion and retrograde solubility. Research on karst evolution has primarily focused on independent mixing corrosion (MC), while the synergistic effect of mixing corrosion and retrograde solubility (MR) has received limited attention. This study employs a previously developed hydro-thermal-chemical coupled model to analyze the early karstification of a limestone basin system recharged by meteoric and cross-formational waters, varying in $P\left({\text{CO}}_2\right)$, Ca²⁺ concentrations, and temperatures. The model incorporates structural heterogeneity and inflow aggressiveness to simulate two scenarios: MC and MR, for comparison. The results show that MC is more likely to occur in shallow aquifers, promoting preferential pathways along the water table. In contrast, MR not only accelerates dissolution at the water table but also increases flow fluxes and the extent of karstification at greater depths. As the decreasing aggressiveness of meteoric water weakens the nonlinear kinetics of dissolution, the duration of early karstification by MC is significantly longer than that of MR. In the shorter karst evolution process driven by MR, increased flow fluxes and conduit diameters at greater depths facilitate the development of longer vertical permeable tunnels along the faults, while hindering conduits enlargement at the water table. These findings reveal distinct modes of karstification for MC and MR, highlighting the significant role of heat and chemistry heterogeneity in karst evolution. This study provides deeper insights into carbonate reservoirs and offers practical implications for improving the efficiency of hydrothermal resource exploitation and geological CO₂ storage.