A Comprehensive Review of Geothermal Reservoirs: Current Understanding and Future Outlook

Underground geothermal resources as clean energy have gained global attention to fulfill energy needs and contribute towards the carbon net zero goal. However, energy extraction from geothermal resources is not straightforward due to complex underground geological conditions. This review study focuses on key aspects associated with the geothermal energy system, its development, associated challenges, and global projects. The study highlights various stimulation techniques which can be used for the development of geothermal resources. The CO₂ based fracturing method offers dual benefits of fracturing at reduced breakdown pressure and carbon sequestration, while utilization of abandoned oil and gas wells can significantly reduce drilling costs. Additionally, this study discuss about the key operational challenges for the geothermal development including formation damage, cementing failure, and high-temperature drilling constraints, emphasizing the need for advanced materials and monitoring techniques. From an economic perspective, drilling remains the most capital-intensive phase, particularly in EGS projects. Global project analyses further show that, while geothermal adoption is growing, wider scalability requires targeted policy support and technology innovation. This comprehensive review covers geothermal extraction from its exploration to production, enhancing knowledge about these resources and their significant contribution to a sustainable energy future. Our findings emphasize the need for continued innovation in drilling and extraction technologies as well as a deeper understanding of geomechanical properties of geothermal reservoirs. Future research should focus on optimizing these systems to enhance their efficiency and reduce environmental impacts, for broader adoption and integration into the overall energy supply.