| Abstract |
Because they are natural phenomena, no two geothermal resources are identical; they all have some features that make for easy development and some that are a disadvantage, and the range of features differs from resource to resource. The features themselves can be recognised because they crop up in many geothermal resources; it is the mix of features that differs from one resource to another. In essence, a geothermal development is relatively simple; geothermal fluid is taken from the ground, heat is extracted and the cooled fluid is disposed of, normally by injecting back into the ground. The resource to be used is the thermal energy, which is contained in the body of rock that has been heated over a geological time period either by conduction or by hot geothermal fluid rising from depth. The rate of hot upflow is impossible to estimate accurately, and while it can be tapped by wells, it is the energy stored in the rock and the water or steam within them that is usually considered to be the resource, not necessarily the upflow. The thermal energy is transported to the surface by the fluid flowing through the reservoir to geothermal wells which have been drilled into the resource. The fluid may be single phase water, single phase steam or a mixture of steam and water. The actual quantities of the phases will be governed by the heat content or enthalpy of the fluid in the resource local to the wells. |