Why do enhanced geothermal systems inject water into fractured underground rock?

Enhanced geothermal systems (EGS) inject water into fractured underground rock primarily to overcome the lack of natural permeability in hot, dry rock formations.12

In many locations, geothermal resources are trapped in rock that contains little to no water and is insufficiently permeable for natural fluid flow. To harness this energy, EGS technology employs high-pressure water injection to create new fissures or force open existing fractures within the deep, hot rock. This process, which mirrors techniques used in fracking, transforms the rock into a permeable reservoir.123

Once the fracture system is established, the injected water acts as a heat transfer fluid. As it circulates through the hot, fractured rock, it absorbs thermal energy and is then returned to the surface to drive turbines for electricity generation. This method allows for the extraction of geothermal energy in non-volcanic and non-seismic regions where traditional, naturally occurring steam or hot water reservoirs are unavailable. However, it is important to note that these high-pressure injection techniques carry the environmental risk of inducing seismic activity.123