ABSTRACT
This chapter explores new, promising means of developing geothermal systems. A main arena for this form of development centers on engineered or enhanced geothermal systems (EGSs). Unlike conventional hydrothermal systems, where the geothermal uid (either liquid or vapor) is naturally circulating in the reservoir and can be easily produced and reinjected due to good inherent permeability, in an EGS uid circulation must be stimulated articially. This is because the rock reservoir has little or no water or the permeability is so low that the water cannot be efciently removed to carry heat (energy) to the surface to support a power plant. As such, systems of low water and/or permeability are also referred to as hot dry rock (HDR) or petraheat. To develop them for possible use requires articial stimulation (enhancement or engineering). In EGSs, rock permeability is commonly enhanced by pumping cold water under pressure into the target region. This process has the effect of expanding any existing fractures and producing additional fractures due to thermal contraction. The injected water ows through the enhanced existing fractures, becoming heated as it moves toward production wells. It then ows to the surface to support either a ash or a binary geothermal power plant, depending on the uid’s attained temperature and ow rate (Figure 11.1).
