ABSTRACT
The ow of uids, whether steam or liquid, is fundamental for the extraction of heat from the Earth that can be used by society. If no uids are present or the uids are prevented from owing, obtaining geothermal energy, regardless of how hot the rocks are, becomes complicated. It requires expensive technical intervention to introduce uids or make uids ow or both; this is the realm of engineered or enhanced geothermal systems (EGSs). To understand how uids move, we need to discuss the roles of porosity and permeability of rock materials.
