The Paris Agreement and COP28 decision summary clearly emphasize the innovation in renewable energy technologies and the transition away from fossil fuels to meet the net zero target practically. In this regard, microbial metabolism provides a green and eco-friendly solution for the mitigation of notorious greenhouse gas (carbon dioxide) and producing biofuel in the form of energy-dense biomethane. However, this biological conversion of carbon dioxide into biomethane requires a bioreactor that can provide the optimum reaction boundary conditions. The depleted petroleum reservoirs, given favorable ecological conditions such as temperatures below 80°C, pH levels ranging from 3 to 8, salinity within 3-7%, and pressure up to 500 bar, have substantial potential to function as excellent geo-bioreactors for microbial metabolism process. The primary motivation for this study is to explore the utilization of depleted hydrocarbon reservoirs as a geo-bioreactor for biomethanation. This study will further focus on important technical issues like the impact of physicochemical factors of the reservoir on reaction rates, nutrient supply, gas injection and recovery efficiency, reservoir mineralogy and porosity, and mechanisms of gas losses through adsorption, absorption, and dissolution

Microbial methanogenesis,depleted petroleum reservoir,CO2 biological conversion,geo-bioreactor