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Locating an Active Fault Zone in Coso Geothermal Field by Analyzing Seismic Guided Waves From Microearthquake Data

Description: Active fault systems usually provide high-permeability channels for hydrothermal outflow in geothermal fields. Locating such fault systems is of a vital importance to plan geothermal production and injection drilling, since an active fault zone often acts as a fracture-extensive low-velocity wave guide to seismic waves. We have located an active fault zone in the Coso geothermal field, California, by identifying and analyzing a fault-zone trapped Rayleigh-type guided wave from microearthquake data. The wavelet transform is employed to characterize guided-wave's velocity-frequency dispersion, and numerical methods are used to simulate the guided-wave propagation. The modeling calculation suggests that the fault zone is {approx} 200m wide, and has a P wave velocity of 4.80 km/s and a S wave velocity of 3.00 km/s, which is sandwiched between two half spaces with relatively higher velocities (P wave velocity 5.60 km/s, and S wave velocity 3.20 km/s). zones having vertical or nearly vertical dipping fault planes.
Date: January 26, 1995
Creator: Lou, M.; Malin, P. E. & Rial, J. A.
Partner: UNT Libraries Government Documents Department

Interpretation of pre- and post-fracturing well tests in a geothermal reservoir

Description: Pre- and post-fracturing well tests in TG-2 well drilled next to the Matsukawa field are interpreted for evaluating effects of a massive hydraulic fracturing treatment. The interpreted data include multiple-step rate tests, a two-step rate test, and falloff tests. Pressure behaviors of massive hydraulic fracturing are matched by a simulator of dynamic fracture option. Fracture parting pressures can be evaluated from the multiple-step rate test data. The multiple-step rates during the massive hydraulic fracturing treatment show that multiple fractures have been induced in sequence. Although the pre-fracturing falloff tests are too short, fracture propagation can be evaluated qualitatively from the falloff data. Interpretation of the falloff test immediately after the MHF suggests that extensive fractures have been created by the MHF, which is verified by simulation. The post-fracturing falloff tests show that the fractures created by the MHF have closed to a great degree.
Date: January 26, 1995
Creator: Arihara, Norio; Fukagawa, Hiroshi; Hyodo, Masami & Abbaszadeh, Maghsood
Partner: UNT Libraries Government Documents Department

An investigation of radial tracer flow in naturally fractured reservoirs

Description: This study presents a general solution for the radial flow of tracers in naturally fractured reservoirs. Continuous and finite step injection of chemical and radioactive tracers are considered. The reservoir is treated as being composed of two regions: a mobile region where longitudinal dispersion and convection take place and a stagnant region where only diffusion and adsorption are allowed. Radioactive decay is considered in both regions. The model of this study is thoroughly compared to those previously presented in literature by Moench and Ogata, Tang et al., Chen et al., and Hsieh et al. The solution is numerically inverted by means of the Crump algorithm. A detailed validation of the model with respect to solutions previously presented and/or simplified physical conditions solutions (i.e., homogeneous case) or limit solutions (i.e., for short times) was carried out. The influence of various dimensionless parameters that enter into the solution was investigated. A discussion of results obtained through the Crump and Stehfest algorithm is presented, concluding that the Crump method provides more reliable tracer concentrations.
Date: January 1, 1991
Creator: Jetzabeth, Ramirez-Sabag; Fernando, Samaniego V.; Jesus, Rivera R. & Rodriguez, Fernando
Partner: UNT Libraries Government Documents Department

Experimental study of two-phase flow in rough fractures

Description: Two-phase (air-water) flow experiments were conducted in horizontal artificial fractures. The fractures were between glass plates (1 x 0.5 m) artificially roughened by gluing a layer of glass beads of Imm diameter. Three rough fractures were studied: one with the two surfaces in contact, and two without contact. Videotape observations revealed flow structures similar to those observed in two-phase flow in pipes, with structures depending upon the gas and liquid flow rates. The data of flow rates, pressure gradients and saturations were interpreted using the generalized Darcy's law. Relative permeabilities curves were found to be similar to classical curves in porous medium, but not unique functions of saturations. The sum of gas and liquid relative permeabilities were found to be less than one at all saturations.
Date: January 1, 1992
Creator: Fourar, M.; Bories, S. & Lenormand, R.
Partner: UNT Libraries Government Documents Department

Laboratory measurements on reservoir rocks from The Geysers geothermal field

Description: A suite of laboratory measurements have been conducted on Geysers metagraywacke and metashale recovered from a drilled depth of 2599 to 2602 meters in NEGU-17. The tests have been designed to constrain the mechanical and water-storage properties of the matrix material. Various measurements have been made at a variety of pressures and at varying degrees of saturation. Both compressional and shear velocities exhibit relatively little change with effective confining pressure. In all of the samples, water saturation causes an increase in the compressional velocity. In some samples, saturation results in a moderate decrease in shear velocity greater in magnitude than would be expected based on the slight increase in bulk density. It is found that the effect of saturation on the velocities can be quantitatively modeled through a modification of Biot-Gassmann theory to include weakening of the shear modulus with saturation. The decrease is attributed to chemo-mechanical weakening caused by the presence of water. The degree of frame weakening of the shear modulus is variable between samples, and appears correlated with petrographic features of the cores. Two related models are presented through which we can study the importance of saturation effects on field-scale velocity variations. The model results indicate that the saturation effects within the matrix are significant and may contribute to previously observed field anomalies. The results help to define ways in which we may be able to separate the effects of variations in rock properties, caused by phenomena such as degree of fracturing, from similar effects caused by variations in matrix saturation. The need for both compressional and shear velocity data in order to interpret field anomalies is illustrated through comparisons of model results with the field observations.
Date: January 26, 1995
Creator: Boitnott, G.N.
Partner: UNT Libraries Government Documents Department

Laboratory measurement of sorption in porous media

Description: A new apparatus for measuring steam adsorption-desorption isothermally on rock samples has been installed and initial runs made for rock samples from geothermal reservoirs. The amounts adsorbed measured in these experiments are the same order of magnitude as previous experiments.
Date: January 1, 1992
Creator: Harr, M. S.; Pettit, P. & Ramey, J. J., Jr.
Partner: UNT Libraries Government Documents Department

Proceedings of the Workshop on Geothermal Reservoir Engineering: 1977

Description: The Third Workshop on Geothermal Reservoir Engineering convened at Stanford University on December 14, 1977, with 104 attendees from six nations. In keeping with the recommendations expressed by the participants at the Second Workshop, the format of the Workshop was retained, with three days of technical sessions devoted to reservoir physics, well and reservoir testing, field development, and mathematical modeling of geothermal reservoirs. The program presented 33 technical papers, summaries of which are included in these Proceedings. Although the format of the Workshop has remained constant, it is clear from a perusal of the Table of Contents that considerable advances have occurred in all phases of geothermal reservoir engineering over the past three years. Greater understanding of reservoir physics and mathematical representations of vapor-dominated and liquid-dominated reservoirs are evident; new techniques for their analysis are being developed, and significant field data from a number of newer reservoirs are analyzed. The objectives of these workshops have been to bring together researchers active in the various physical and mathematical disciplines comprising the field of geothermal reservoir engineering, to give the participants a forum for review of progress and exchange of new ideas in this rapidly developing field, and to summarize the effective state of the art of geothermal reservoir engineering in a form readily useful to the many government and private agencies involved in the development of geothermal energy. To these objectives, the Third Workshop and these Proceedings have been successfully directed. Several important events in this field have occurred since the Second Workshop in December 1976. The first among these was the incorporation of the Energy Research and Development Administration (ERDA) into the newly formed Department of Energy (DOE) which continues as the leading Federal agency in geothermal reservoir engineering research. The Third Workshop under the Stanford Geothermal Program was supported ...
Date: December 15, 1977
Creator: Ramey, H. J., Jr. & Kruger, P. (eds.)
Partner: UNT Libraries Government Documents Department

Seventeenth workshop on geothermal reservoir engineering: Proceedings

Description: PREFACE The Seventeenth Workshop on Geothermal Reservoir Engineering was held at Stanford University on January 29-31, 1992. There were one hundred sixteen registered participants which equaled the attendance last year. Participants were from seven foreign countries: Italy, Japan, United Kingdom, France, Belgium, Mexico and New Zealand. Performance of many geothermal fields outside the United States was described in the papers. The Workshop Banquet Speaker was Dr. Raffaele Cataldi. Dr. Cataldi gave a talk on the highlights of his geothermal career. The Stanford Geothermal Program Reservoir Engineering Award for Excellence in Development of Geothermal Energy was awarded to Dr. Cataldi. Dr. Frank Miller presented the award at the banquet. Thirty-eight papers were presented at the Workshop with two papers submitted for publication only. Dr. Roland Horne opened the meeting and the key note speaker was J.E. ''Ted'' Mock who discussed the DOE Geothermal R. & D. Program. The talk focused on aiding long-term, cost effective private resource development. Technical papers were organized in twelve sessions concerning: geochemistry, hot dry rock, injection, geysers, modeling, and reservoir mechanics. Session chairmen were major contributors to the program and we thank: Sabodh Garg., Jim Lovekin, Jim Combs, Ben Barker, Marcel Lippmann, Glenn Horton, Steve Enedy, and John Counsil. The Workshop was organized by the Stanford Geothermal Program faculty, staff, and graduate students. We wish to thank Pat Ota, Ted Sumida, and Terri A. Ramey who also produces the Proceedings Volumes for publication. We owe a great deal of thanks to our students who operate audiovisual equipment and to Francois Groff who coordinated the meeting arrangements for the Workshop. Henry J. Ramey, Jr. Roland N. Horne Frank G. Miller Paul Kruger William E. Brigham Jean W. Cook -vii
Date: January 31, 1992
Creator: Ramey, H.J. Jr.; Kruger, P.; Miller, F.G.; Horne, R.N.; Brigham, W.E. & Cook, J.W. (Stanford Geothermal Program)
Partner: UNT Libraries Government Documents Department

Simulating wellflow of high-nonocondensable-gas geofluids using laboratory measurements on secondary fluids

Description: An experimental simulation of an actual steam-water geothermal well based on field data obtained in New Zealand is carried out in a two-phase flow facility using dichlorotetrafluoroethane, known commercially as refrigerant 114. The simulation of steam-water flow is accomplished by a similarity theory which is achieved by using appropriate dimensionless numbers; namely, the Mach, Froude, and Reynolds numbers at the flashing front. The theory is used to scale the flow properties from that of water to that of refrigerant 114 in the two-phase region, and permits the prediction of steam-water characteristics in a flowing well, under much reduced pressure and temperature levels. Two experimental series were conducted to confront the similarity theory with actual measurements from a flowing well with significant noncondensable gases. Experimental results using refrigerant 114 indicate that the pressure distribution along the pipe can be predicted accurately in the two-phase region of a geothermal well.
Date: January 1, 1991
Creator: Laoulache, R.N. & Dipippo, R.
Partner: UNT Libraries Government Documents Department

Study of desorption in a vapor dominated reservoir with fractal geometry

Description: This paper is an attempt to model well decline in a vapor dominated reservoir with fractal geometry. The fractal network of fractures is treated as a continuum with characteristic anomalous diffusion of pressure. A numerical solver is used to obtain the solution of the partial differential equation including adsorption in the fractal storage space. The decline of the reservoir is found to obey the empirical hyperbolic type relation when adsorption is not present. Desorption does not change the signature of the flow rate decline but shifts it on the time/flow rate axis. Only three out of six model parameters can be estimated from field data, due to the linear correlation between parameters. An application to real well data from The Geysers field is presented together with the estimated reservoir, fractal space and adsorption parameters. Desorption dominated flow is still a questionable approximation for flow in fractal objects.
Date: January 26, 1995
Creator: Tudor, Monica; Horne, Roland N. & Hewett, Thomas A.
Partner: UNT Libraries Government Documents Department

Simulating a challenging water dominated geothermal system: The Cerro Prieto field, Baja California, Mexico

Description: A three dimensional, multiphase, numerical simulation model of the Cerro Prieto field was developed and used to verify that the present installed capacity (620 MW) can be sustained for 30 years and to evaluate the impact of an 80 MW addition to the installed capacity in the NE-E of the field on the present production areas. Cerro Prieto is the largest known water-dominated geothermal reservoir in the world, with more than 175 wells drilled to date and 17 years of production history. Wells here produce fluids of varying enthalpy, from moderate-temperature water to dry steam. The varying enthalpy and a complex interaction between the reservoir and the surrounding aquifer posed a real simulation challenge. The simulation approach used to reproduce the major features of the initial-state and the production history of the field is discussed in this paper. From this study it was concluded that the field is capable of sustaining its present 620 MW total installed capacity for 30 years and the addition of the proposed 80 MW should have a negligible effect on the present production area.
Date: January 1, 1991
Creator: Antunez, E.U.; Menzies, A.J. & Sanyal, S.K.
Partner: UNT Libraries Government Documents Department