Carbon capture and storage for long-term and safe sealing with constrained natural CO2 analogs

Carbon capture and storage for long-term sealing is one of the most promising approaches to mitigate global climate change. However, maximum capture amount and long-term safety of carbon dioxide storage in geological scenarios must be ensured. A case of a natural CO2 storage analog of the Huangqiao CO2-oil reservoir in the northern Jiangsu Basin, eastern China, is presented that can safely preserve carbon for millions of years, despite the mantle CO2-rich fluid having substantially altered the sandstone reservoirs. The calcite in the sandstone was significantly reduced by dissolution, thereby improving the CO2 storage capacity. Meanwhile, the mantle CO2-rich fluid advanced the precipitated calcite cement in the fractures of the mudstone caprock as it migrated upward, serving to self-seal the fractures and enhance the sealing capacity of CO2 storage. We numerically simulated artificial CO2 injection for 30 years in the depleted oil reservoir of Jurong near the Huangqiao CO2-oil reservoir; the maximum amount of CO2 injected into a single well can reach 5.43 x 106 t and increase the formation pressure by up to 95 bar. After injection, the saturation of gas-phase CO2 did not decrease remarkably over the following 300 years. No projected rapid CO2 leaked through fractures, owing to the selfsealing of fractures through calcite cement. This suggests that the depleted petroleum reservoir with an assemblage of sandstone reservoirs and overlying mudstone caprocks could be suitable for long-term and safe carbon capture and storage in geological formations.