<p>Green energy sources, such as geothermal energy, have become more prevalent in recent years to combat global warming. Although numerous studies have been conducted on homogeneous geothermal reservoirs, little is known about the effects of heterogeneities on deep geothermal reservoir performance. In this study, the behavior of Hot Dry Rock (HDR) reservoirs is studied under the existence of various thermal, mechanical, and hydraulic heterogeneities. Thermo-hydro-mechanical (THM) analyses are carried out to analyze HDR reservoir behavior. HDR reservoirs are surrounded by impermeable rock that conveys heat, but no fluid flows. Firstly, the study proposes efficient dimensions for taking the surrounding unfractured rocks into account. Next, the model is used to analyze different types of mechanical, thermal, and hydraulic heterogeneities. While mechanical and thermal heterogeneities have negligible effects on HDR reservoir performance, hydraulic heterogeneity significantly impacts the system's performance. The obtained results demonstrate a decrease in geothermal system service life with increasing hydraulic heterogeneity. Deep geothermal energy extraction can also cause some impacts on the environment, such as surface deformations. According to the study, reservoir deformation increases as hydraulic heterogeneity increases, making it important to consider when modeling heat extraction from HDR reservoirs. It is also shown that drilling both types of wellbores down into the least permeable layer results in better heat extraction performance, which is identified based on analyzing several injection and production cases.</p>