Enhanced/Engineered Geothermal Systems
Enhanced or Engineered Geothermal Systems is the contemporary name for non-hydrothermal reservoirs formerly termed as Hot Dry Rock (HDR) reservoirs. They differ from hydrothermal resources as the reservoir may be "engineered" where needed, and therefore utilize a resource that ubiquitously available - the reservoir is created by drilling to access suitably hot rock at depth, and to then extract heat from this through some mechanism. The usual method is to circulate cold water from the surface to the deep reservoir, that is then heated, and then returned to the ground surface where the thermal energy is converted to electrical energy via a turbine.
HDR or EGS is distinct from hydrothermal resources as little fluid is usually present within the reservoir. Instead, water is circulated as a heat transfer medium, using the ground as a large geological heat exchanger. Although attractive as a low carbon heat energy source, important issues remain in reducing the expense of EGS. These include substantially reducing drilling costs, to access the reservoir, and in ensuring that a long-lived and high-throughput reservoir may be developed.
Our interests in HDR/EGS have been related to developing an understanding of the mechanisms of permeability enhancement that develop in these reservoirs, how this affects the longevity of heat supply. These investigations have been both analytical, and experimental, the latter to define the role of rates of dissolution and precipitation on the evolution of permeability on critically stressed fractures.
Elsworth, D. (1990). A comparative evaluation of the parallel flow and spherical reservoir models of HDR geothermal systems. J. Volcanology and Geothermal Res., Vol. 44, pp. 283 - 293. [pdf]
Elsworth, D. (1989). Thermal recovery from a multiple stimulated HDR reservoir. Geothermics, Vol. 18, No. 5/6, pp. 761-774. [pdf]
Elsworth, D. (1989). Theory of thermal recovery from a spherically stimulated HDR reservoir. J. Geophys. Res., Vol. 94, No. B2, pp. 1927 - 1934. [pdf]
Elsworth, D. and Xiang, J. (1989). A reduced degree of freedom model for permeability enhancement in blocky rock. Geothermics, Vol. 18, No. 5/6, pp. 691-709. [pdf]
Elsworth, D. (1989). Thermal permeability enhancement of blocky rocks: plane and radial flow. Proceedings E.E.C. and C.N.R.S. Workshop of Fluid Flow Through Strong Fractured Rocks, Garchy, France, April. 24 pages. and Int. J. R. Mech. Min. Sci., Vol. 26, No. 3/4, pp. 329 - 339. [pdf]