Decarbonation generates considerable CO2 in sedimentary basin environments: Implications for the formation of secondary pores

Carbon dioxide (CO₂) is a crucial acidic component in sedimentary basins, significantly influencing the formation and evolution of dissolution-type reservoirs. While carbonate decarbonation is a primary source of CO₂, its occurrence under basin conditions remains debated. To address this, we conducted high-temperature, high-pressure in situ and ex situ experiments on the CaCO₃-SiO₂-H₂O, CaMg(CO₃)₂-SiO₂-H₂O, and CaCO₃-SiO₂-H₂O-MgCl₂ systems to investigate decarbonation conditions and mechanisms. The results indicate that temperature is the dominant controlling factor: calcite decarbonation occurs above 275 °C, while magnesium-rich diagenetic systems react at temperatures as low as 100 °C. Pressure inhibits decarbonation, and system openness determines the solid-phases products. In nearly closed systems, kerolite forms and dehydrates into talc, while calcite undergoes dolomitization in the presence of Mg-rich fluids. In open systems, talc dominates, with less dolomitization, and the release of CO₂ promotes decarbonation. Based on these results and previous case studies of silica- and magnesium-rich hydrothermal fluids interacting with carbonate strata, we propose that carbonate decarbonation is a significant source of CO₂ in sedimentary basins, contributing to the development of dissolution-type reservoirs. Further research should explore the implications of these mechanisms for hydrocarbon reservoir formation.