Sulfate reduction persists under carbon dioxide storage conditions in depleted oil reservoir microbial communities

Geological carbon capture and storage (CCS) is widely recognised as a critical strategy for mitigating climate change through the long-term sequestration of carbon dioxide in deep subsurface formations, including saline aquifers and depleted oil and gas reservoirs. Oil reservoirs host diverse and metabolically active microbial communities that are shaped by long-term production practices and secondary recovery operations, including seawater injection. Previous field and laboratory studies have shown that carbon dioxide injection can significantly alter subsurface microbial activity, in some cases stimulating metabolic pathways such as methanogenesis or carbon dioxide fixation, with potential consequences for storage security. However, the extent and direction of microbial responses remain site-specific and poorly constrained.This study investigated the response of mature oilfield microbial communities to carbon dioxide rich conditions representative of geological storage environments using 12 month microcosm experiments.