Modeling the impact of evaporites on burial fluid-rock interactions in carbonate reservoirs

Abstract

Carbonate-evaporite successions can serve as important hydrocarbon reservoirs. However, the unique petrophysical properties of evaporites and various carbonate-evaporite lithological associations have impeded understanding of the complex fluid-rock interactions and diagenetic evolution of these reservoirs. Here we present numerical modeling of the diagenetic mineral-porosity evolution in various fluid‑carbonate-evaporite systems and compare them with those in carbonate only strata. The high thermal conductivity and low permeability of thick evaporites (e.g., salt and anhydrite) could result in elevated temperature in supra-salt environment and decreased temperature and overpressure in pre-salt environment. These conditions promote carbonate precipitation from in situ pore fluids in supra-salt formations and dissolution in pre-salt formations. Besides, evaporite interlayers can function as pressure and fluid seals, limiting the influence of diagenetic geochemical reactions. Mineral dissolution-precipitation primarily occurs near the first set of dense evaporite layer in the direction of fluid transport. From the perspective of porosity preservation, the cementation pattern (type and intensity) and porosity distribution are jointly controlled by carbonate-evaporite lithological associations, fluid properties, and flow paths. High-quality reservoirs may form in all three burial environments: pre-salt, inter-salt, and supra-salt strata. The results contribute to a better understanding of burial fluid-rock interactions and the mechanisms behind reservoir formation and preservation in carbonate-evaporite systems.