6,032 Matching Results

Search Results

Advanced search parameters have been applied.

A PLAUSIBLE TWO-DIMENSIONAL VERTICAL MODEL OF THE EAST MESA GEOTHERMAL FIELD, CALIFORNIA, U.S.A

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

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

Microbial impacts on geothermometry temperature predictions

Description: Conventional geothermometry approaches assume that the composition of a collected water sample originating in a deep geothermal reservoir still reflects chemical equilibration of the water with the deep reservoir rocks. However, for geothermal prospecting samples whose temperatures have dropped to <120°C, temperature predictions may be skewed by the activity of microorganisms; microbial metabolism can drastically and rapidly change the water’s chemistry. We hypothesize that knowledge of microbial impacts on exploration sample geochemistry can be used to constrain input into geothermometry models and thereby improve the reliability of reservoir temperature predictions. To evaluate this hypothesis we have chosen to focus on sulfur cycling, because of the significant changes in redox state and pH associated with sulfur chemistry. Redox and pH are critical factors in defining the mineral-fluid equilibria that form the basis of solute geothermometry approaches. Initially we are developing assays to detect the process of sulfate reduction, using knowledge of genes specific to sulfate reducing microorganisms. The assays rely on a common molecular biological technique known as quantitative polymerase chain reaction (qPCR), which allows estimation of the number of target organisms in a particular sample by enumerating genes specific to the organisms rather than actually retrieving and characterizing the organisms themselves. For quantitation of sulfate reducing genes using qPCR, we constructed a plasmid (a piece of DNA) containing portions of two genes (known as dsrA and dsrB) that are directly involved with sulfate reduction and unique to sulfate reducing microorganisms. Using the plasmid as well as DNA from other microorganisms known to be sulfate reducers or non-sulfate reducers, we developed qPCR protocols and showed the assay’s specificity to sulfate reducers and that a qPCR standard curve using the plasmid was linear over >5 orders of magnitude. As a first test with actual field samples, the assay was applied to DNA ...
Date: February 1, 2013
Creator: Fujita, Yoshiko; Reed, David W.; Nowak, Kaitlyn R.; Thompson, Vicki S.; McLing, Travis L. & Smith, Robert W.
Partner: UNT Libraries Government Documents Department

Heat and Mass Transfer in a Fault-Controlled Geothermal Reservoir Charged at Constant Pressure

Description: A two-dimensional mathematical model of a fault controlled geothermal reservoir has been developed. Heated lighter water, rising in the fault, is assumed to charge a reservoir which, in turn, is overlain by a thin impermeable, thermally conducting cap rock. The mass flow rate or the pressure associated with the charging process at the fault inlet is unknown and can only be estimated. Thus, in this paper, the pressure in the fault at the bottom of the reservoir is assumed to be prescribed. Quasi-analytic solutions for the velocity, pressure, and temperature are obtained in the fault-reservoir system for a high Rayleigh number flow. In this approximation, the upwelling fluid does not cool off appreciably until it reaches the cold upper boundary of the reservoir and encounters conductive heat loss. This thermal boundary layer, which is thin at the top of the fault, grows outward laterally and occupies the full thickness of the aquifer far away from the fault. The mathematical model is based on the flow of liquid water in a saturated porous medium. The solution techniques involve the combination of perturbation methods, boundary layer theory and numerical methods. The analysis of this generic model can be applied to liquid dominated geothermal systems where the thickness of the impermeable caprock is very small compared to the depth of the reservoir.
Date: December 1, 1981
Creator: Goyal, K.P. & Narasimhan, T.N.
Partner: UNT Libraries Government Documents Department