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Description: Development of enhanced geothermal systems (EGS) will require creation of a reservoir of sufficient volume to enable commercial-scale heat transfer from the reservoir rocks to the working fluid. A key assumption associated with reservoir creation/stimulation is that sufficient rock volumes can be hydraulically fractured via both tensile and shear failure, and more importantly by reactivation of naturally existing fractures (by shearing) to create the reservoir. The advancement of EGS greatly depends on our understanding of the dynamics of the intimately coupled rock-fracture-fluid system and our ability to reliably predict how reservoirs behave under stimulation and production. In order to increase our understanding of how reservoirs behave under these conditions, we have developed a physics-based rock deformation and fracture propagation simulator by coupling a discrete element model (DEM) for fracturing with a continuum multiphase flow and heat transport model. In DEM simulations, solid rock is represented by a network of discrete elements (often referred as particles) connected by various types of mechanical bonds such as springs, elastic beams or bonds that have more complex properties (such as stress-dependent elastic constants). Fracturing is represented explicitly as broken bonds (microcracks), which form and coalesce into macroscopic fractures when external load is applied. DEM models have been applied to a very wide range of fracturing processes from the molecular scale (where thermal fluctuations play an important role) to scales on the order of 1 km or greater. In this approach, the continuum flow and heat transport equations are solved on an underlying fixed finite element grid with evolving porosity and permeability for each grid cell that depends on the local structure of the discrete element network (such as DEM particle density). The fluid pressure gradient exerts forces on individual elements of the DEM network, which therefore deforms and fractures. Such deformation/fracturing in turn changes ...
Date: February 1, 2010
Creator: Podgorney, Robert; Huang, Hai & Gaston, Derek
Partner: UNT Libraries Government Documents Department


Description: A two-dimensional conceptual model of the East Mesa geothermal system is developed on the basis of the existing geological, geophysical geochemical, heat flux, and borehole logging data. A fault called the Mesa Fault is assumed to charge the reservoir, which is overlaid by a clay-rich cap. The mathematical model :is based on the flow of liquid water in a saturated porous medium. To obtain temperature-depth distributions similar to those measured at the site, we assume that the liquid is convecting at a high Rayleigh number. In this approximation, liquid rises up the fault and spreads into the near regions of the reservoir isothermally. The cooling effect of the surface on the flow in the reservoir is confined to a thin layer adjacent to the cap-reservoir interface near the fault. This layer grows with the distance from the fault. Eventually, the full depth of the reservoir is cooled by the surface. Results are obtained for the velocities, pressures, and temperatures of the entire system (fault zone, aquifer and clay cap). Finally we compare the heat flux predicted for the surface to that measured at the site in shallow wells.
Date: March 1980
Creator: Goyal, K. P. & Kassoy, D. R.
Partner: UNT Libraries Government Documents Department

Life Cycle Water Consumption and Water Resource Assessment for Utility-Scale Geothermal Systems: An In-Depth Analysis of Historical and Forthcoming EGS Projects

Description: This report is the third in a series of reports sponsored by the U.S. Department of Energy Geothermal Technologies Program in which a range of water-related issues surrounding geothermal power production are evaluated. The first report made an initial attempt at quantifying the life cycle fresh water requirements of geothermal power-generating systems and explored operational and environmental concerns related to the geochemical composition of geothermal fluids. The initial analysis of life cycle fresh water consumption of geothermal power-generating systems identified that operational water requirements consumed the vast majority of water across the life cycle. However, it relied upon limited operational water consumption data and did not account for belowground operational losses for enhanced geothermal systems (EGSs). A second report presented an initial assessment of fresh water demand for future growth in utility-scale geothermal power generation. The current analysis builds upon this work to improve life cycle fresh water consumption estimates and incorporates regional water availability into the resource assessment to improve the identification of areas where future growth in geothermal electricity generation may encounter water challenges. This report is divided into nine chapters. Chapter 1 gives the background of the project and its purpose, which is to assess the water consumption of geothermal technologies and identify areas where water availability may present a challenge to utility-scale geothermal development. Water consumption refers to the water that is withdrawn from a resource such as a river, lake, or nongeothermal aquifer that is not returned to that resource. The geothermal electricity generation technologies evaluated in this study include conventional hydrothermal flash and binary systems, as well as EGSs that rely on engineering a productive reservoir where heat exists, but where water availability or permeability may be limited. Chapter 2 describes the approach and methods for this work and identifies the four power plant ...
Date: November 5, 2013
Creator: Clark, Corrie E.; Harto, Christopher B.; Schroeder, Jenna N.; Martino, Louis E. & Horner, Robert M.
Partner: UNT Libraries Government Documents Department

Idaho Geothermal Handbook

Description: Idaho's energy problems have increased at alarming rates due to their dependency on imports of gas and oil. The large hydroelectric base developed in Idaho has for years kept the electric rates relatively low and supplied them with energy on a consumer demand basis. However, this resource cannot be 4expected to meet their growing demands in the years to come. Energy alternatives, in whatever form, are extremely important to the future welfare of the State of Idaho. This handbook addresses the implications, uses, requirements and regulations governing one of Idaho's most abundant resources, geothermal energy. The intent of the Idaho Geothermal Handbook is to familiarize the lay person with the basis of geothermal energy in Idaho. The potential for geothermal development in the State of Idaho is tremendous. The authors hope this handbook will both increase your knowledge of geothermal energy and speed you on your way to utilizing this renewable resource.
Date: July 1, 1979
Creator: Hammer, Gay Davis; Esposito, Louis & Montgomery, Martin
Partner: UNT Libraries Government Documents Department

Seismic Technology Adapted to Analyzing and Developing Geothermal Systems Below Surface-Exposed High-Velocity Rocks Final Report

Description: The objective of our research was to develop and demonstrate seismic data-acquisition and data-processing technologies that allow geothermal prospects below high-velocity rock outcrops to be evaluated. To do this, we acquired a 3-component seismic test line across an area of exposed high-velocity rocks in Brewster County, Texas, where there is high heat flow and surface conditions mimic those found at numerous geothermal prospects. Seismic contractors have not succeeded in creating good-quality seismic data in this area for companies who have acquired data for oil and gas exploitation purposes. Our test profile traversed an area where high-velocity rocks and low-velocity sediment were exposed on the surface in alternating patterns that repeated along the test line. We verified that these surface conditions cause non-ending reverberations of Love waves, Rayleigh waves, and shallow critical refractions to travel across the earth surface between the boundaries of the fast-velocity and slow-velocity material exposed on the surface. These reverberating surface waves form the high level of noise in this area that does not allow reflections from deep interfaces to be seen and utilized. Our data-acquisition method of deploying a box array of closely spaced geophones allowed us to recognize and evaluate these surface-wave noise modes regardless of the azimuth direction to the surface anomaly that backscattered the waves and caused them to return to the test-line profile. With this knowledge of the surface-wave noise, we were able to process these test-line data to create P-P and SH-SH images that were superior to those produced by a skilled seismic data-processing contractor. Compared to the P-P data acquired along the test line, the SH-SH data provided a better detection of faults and could be used to trace these faults upward to the boundaries of exposed surface rocks. We expanded our comparison of the relative value of S-wave and ...
Date: February 28, 2013
Creator: Hardage, Bob A.; DeAngelo, Michael V.; Ermolaeva, Elena; Hardage, Bob A.; Remington, Randy; Sava, Diana et al.
Partner: UNT Libraries Government Documents Department

Sampling Geopressured Fluids: Design Considerations Based on Properties of the H{Sub 2}O-Ch{Sub 4} System

Description: This paper discusses how we can quantitatively estimate, in both the sampler and the wellbore, the geopressured fluid properties that occur during the sampling process. A simple model (an "equation of state") is presented that allows us to estimate thermophysical properties of geopressured fluids. The "equation of state" is applied to compute and discuss fluid properties associated with the different stages of the sampling process.
Date: November 1, 1980
Creator: Iglesias, Eduardo R.
Partner: UNT Libraries Government Documents Department

Subsidence Due to Geothermal Fluid Withdrawal

Description: Single-phase and two-phase geothermal reservoirs are currently being exploited for power production in Italy, Mexico, New Zealand, the U.S. and elsewhere. Vertical ground displacements of upto 4.5 m and horizontal ground displacements of up to 0.5 m have been observed at Wairakei, New Zealand that are clearly attributable to the resource exploitation. Similarly, vertical displacements of about 0.13 m have been recorded at The Geysers, California. No significant ground displacements that are attributable to large-scale fluid production have been observed at Larderello, Italy and Cerro Prieto, Mexico. Observations show that subsidence due to geothermal fluid production is characterized by such features as an offset of the subsidence bowl from the main area of production, time-lag between production and subsidence and nonlinear stress-strain relationships. Several plausible conceptual models, of varying degrees of sophistication, have been proposed to explain the observed features. At present, relatively more is known about the physical mechanisms that govern subsidence than the relevant thermal mechanisms. Although attempts have been made to simulate observed geothermal subsidence, the modeling efforts have been seriously limited by a lack of relevant field data needed to sufficiently characterize the complex field system.
Date: October 1, 1982
Creator: Narasimhan, T. N. & Goyal, K. P.
Partner: UNT Libraries Government Documents Department

Investigation of the Availability of Geothermal Energy for the Demineralization of Saline Water

Description: From Introduction: "The purpose of this investigation was to examine the question of the availability of geothermal energy and in particular the availability of geothermal energy from the Black Hills of South Dakota.
Date: July 1959
Creator: Research and Development Association. School of Mines.
Partner: UNT Libraries Government Documents Department

Geothermal Energy

Description: Geothermal Energy Technology (GET) announces on a bimonthly basis the current worldwide information available on the technologies required for economic recovery of geothermal energy and its use as direct heat or for electric power production.
Date: February 1, 1996
Creator: Steele, B.C.; Harman, G. & Pitsenbarger, J.
Partner: UNT Libraries Government Documents Department

United States geothermal technology: Equipment and services for worldwide applications

Description: This document has two intended audiences. The first part, ``Geothermal Energy at a Glance,`` is intended for energy system decision makers and others who are interested in wide ranging aspects of geothermal energy resources and technology. The second part, ``Technology Specifics,`` is intended for engineers and scientists who work with such technology in more detailed ways. The glossary at the end of the document defines many of the specialized terms. A directory of US geothermal industry firms who provide goods and services for clients around the world is available on request.
Date: May 1, 1995
Partner: UNT Libraries Government Documents Department