Geothermal energy is the naturally occurring energy source under the Earth’s crust in the form of heat. It is used in heating, cooling and electricity generation around the world. Recently, the desire to decrease carbon emissions and curb climate change has inspired the development of energy efficient geothermal energy storage systems. Carbon sequestration, groundwater exploitation and mineral extraction are attempted while extracting geothermal energy. A number of different Thermal Energy Storage (TES) systems have been developed, the most common of which is the Aquifer Thermal Energy Storage (ATES) system. The ATES system is a large-scale geothermal system with complex Thermo-Hydrological-Mechanical-Chemical (THMC) processes determining its rock-fluid interaction. THMC processes also affect wellbore and cement/rock integrity. Coupled THMC modeling is the newest development in characterization and prediction of geothermal systems. In this paper, developments in THMC modeling and their applications in geothermal energy production, Enhanced Geothermal Systems (EGS) and ATES are discussed. Depending upon the scale, and processes studied in the geothermal system, different methodologies in numerical modeling may be adopted.