Enhanced (or engineered) geothermal systems (EGS) have evolved from the hot dry rock concept, implemented for the first time at Fenton Hill in 1977. This paper systematically reviews all of the EGS projects worldwide, based on the information available in the public domain. The projects are classified by country, reservoir type, depth, reservoir temperature, stimulation methods, associated seismicity, plant capacity and current status. Thirty five years on from the first EGS implementation, the geothermal community can benefit from the lessons learnt and take a more objective approach to the pros and cons of ‘conventional’ EGS systems.

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A systematic review of enhanced (or engineered) geothermal systems: past, present and future

9 7 8 3 5 4 0 6 7 3 1 6 3 Mining the Earth’s Heat: Hot Dry Rock Geothermal Energy describes the work carried out by the Los Alamos National Laboratory to turn an idealistic concept – that of drawing useful amounts of energy from the vast underground store of hot rock at reachable depths – into a practical reality. This book provides comprehensive documentation of the over two decades of experiments carried out at the test site at Fenton Hill, New Mexico, where the feasibility of accessing and extracting this vast natural resource was finally demonstrated. It also discusses the numerous technical, administrative, and financial hurdles that had to be overcome along the way. This publication will no doubt prove invaluable to researchers around the world as they strive to move this now-proven technology toward commercial viability. In addition, it is a valuable source of relevant information for anyone interested in the world energy outlook for the 21st century and beyond.

Mining the Earth's Heat: Hot Dry Rock Geothermal Energy

As a new procedure for modeling geothermal energy extraction systems, a two-dimensional modeling technique for subsurface fracture networks on the basis of `fractal geometry` is presented. Models of fracture networks are generated by distributing fractures randomly in space and by using the fractal relation between fracture length r and the number of fractures N expressed with a fractal dimension D as N = Cr(exp -D), where C is a constant that signifies the fracture density within the rock mass. This procedure makes it possible to characterize geothermal reservoirs by parameters measured from field data, such as from core sampling. In this characterization the fracture density parameter C of a geothermal reservoir is used as a parameter to model the subsurface fracture network. Using this fracture network model, the connectivities of the water flow paths between wells are calculated by means of a Monte Carlo simulation, and the result is then compared with that derived from a percolation model. We show that many fewer fractures are required to connect two wells for the fracture network model than for the percolation model. The transmissivities between wells for the fracture network model are also obtained as a function of the fracture density parametermore » C. The results show that the transmissivities in geothermal reservoirs are significantly dependent upon the fracture density of rock mass, and they can be predicted from the fracture density parameter C of the reservoirs.« less

Fractal geometry characterization of geothermal reservoir fracture networks

▪ Abstract Geothermal energy technology is reviewed in terms of its current impact and future potential as an energy source. In general, the geothermal energy resource base is large and well distributed globally. Geothermal systems have a number of positive social characteristics (they are simple, safe, and adaptable systems with modular 1–50 MW [thermal (t) or electric (e)] plants capable of providing continuous baseload, load following, or peaking capacity) and benign environmental attributes (negligible emissions of CO2, SOx, NOx, and particulates, and modest land and water use). Because these features are compatible with sustainable growth of global energy supplies in both developed and developing countries, geothermal energy is an attractive option to replace fossil and fissile fuels. In 1997, about 7,000 MWe of base-load generating capacity and over 15,000 MWt of heating capacity from high-grade geothermal resources are in commercial use worldwide. A key question is whether these levels can grow to ...

Geothermal energy from the earth : Its potential impact as an environmentally sustainable resource

Coupled thermo-hydro-mechanical analysis of stimulation and production for fractured geothermal reservoirs

Hot Dry Rock (HDR) geothermal energy, which utilizes the natural heat contained in the earth's crust, can provide a widely available source of nonpolluting energy. It can help mitigate the continued warming of the earth through the ''greenhouse effect,'' and the accelerating destruction of forests and crops by acid rain, two of the major environmental consequences of our ever-increasing use of fossil fuels for heating and power generation. In addition, HDR, as a readily available source of indigenous energy, can reduce our nation's dependence on imported oil, enhancing national security and reducing our trade deficit. The earth's heat represents an almost unlimited source of energy that can begin to be exploited within the next decade through the HDR heat-mining concept being actively developed in the United States and in several other countries. On a national scale, we can begin to develop this new energy source, using it directly for geothermal power or indirectly in hybrid geothermal/fossil-fueled systems, in diverse applications such as: baseload power generation, direct heat use, feedwater heating in conventional power plants, and pumped storage/load leveling power generation. This report describes the nature of the HDR resource and the technology required to implement the heat-mining concept in severalmore » applications. An assessment of the requirements for establishing HDR feasibility is presented in the context of providing a commercially competitive energy source. 37 refs., 6 figs.« less

J.W. Tester

Papers

Hot Dry Rock geothermal energy--- A new energy agenda for the twenty-first century