The role of reservoir modelling in feasibility studies for HDR geothermal energy exploitation

• Published in: Geothermics 1995-06, Vol.24 (3), p.301-305
• Main Authors: Parker, R.H., Jupe, A.J.
• Format: Article
• Language: English
• ISSN: 0375-6505; 1879-3576
• DOI: 10.1016/0375-6505(95)00022-I

The heat exchanger created from the hot rock formation in the development of the HDR system has been called a geothermal "reservoir". The natural permeability of some rock formations may be sufficient to create a suitable heat exchanger, but it has been found, in the experiments carried out so far, that it has been necessary to enhance the permeability of the rock locally in the heat exchanger by "stimulating" the naturally-occurring rock joints. This stimulation process has involved pumping fluid at high pressure into the joints, thus causing a permanent increase in joint aperture, and thereby increasing the permeability of the stimulated rock mass. Ultimately, the operation of the heat exchanger or reservoir must be cost-effective, and this implies that it must satisfy the following requirements. 1) The temperature and volume of water produced must be high enough for economic exploitation. 2) Resistance to flow through the reservoir (commonly called the reservoir "impedance") must not require too high a consumption of energy to pump water through the system. 3) Water losses from the system to the surrounding rock must be minimised. 4) The rate of cooling of the reservoir rock must be low enough to give the reservoir an economic life. 5) The use of heat from "natural" water flow into the reservoir must be maximised. 6) Chemical and physical degradation of the rock-water interface must not inhibit the economic operation of the system. 7) The chemical composition of the water produced from the system must not adversely affect the operation of surface plant, underground pipework, and if production fluids enter neighbouring systems, unacceptable environmental pollution must be avoided. 8) The risk of physical environmental damage must be minimised. An example of this could be the risk of earthquakes resulting from high pressure injection of water into rock formations.