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R Reactor seepage basins soil moisture and resistivity field investigation using cone penetrometer technology, Savannah River Site, Aiken, South Carolina

Description: The focus of this report is the summer 1999 investigation of the shallow groundwater system using cone penetrometer technology characterization methods to determine if the water table is perched beneath the R Reactor Seepage Basins (RRSBs).
Date: February 17, 2000
Creator: Harris, M.K.
Partner: UNT Libraries Government Documents Department

Multifrequency crosshole EM imaging for reservoir characterization. FY 1994 annual report

Description: Electrical conductivity of sedimentary rocks is controlled by the porosity, hydraulic permeability, temperature, saturation, and the pore fluid conductivity. These rock parameters play important roles in the development and production of hydrocarbon (petroleum and natural gas) resources. For these reasons, resistivity well logs have long been used by geologists and reservoir engineers in petroleum industries to map variations in pore fluid, to distinguish between rock types, and to determine completion intervals in wells. Reservoir simulation and process monitoring rely heavily on the physical characteristics of the reservoir model. Over a period of three years (1991-1993) there was an initial phase of crosshole EM technique development via an informal partnership between LLNL and LBL. Researchers developed field instrumentation to apply to oil field for monitoring EOR thermal processes. Specifically, a prototype single-frequency instrumentation was developed and with this system we have conducted field surveys in four separate locations. Theory and software were developed to interpret these data by providing subsurface images of the electrical conductivity. In spite of our initial success in developing practical EM techniques, we still had severe instrumentation limitations and shortcomings in interpretation for other than simple structures. The field equipment was designed to work only at a single frequency at a time and the transmitter must be opened to change frequencies. The equipment was also significantly noiser at higher frequencies. For high-resolution applications we need to take full advantage of the resolution inherent in the data. The development of a high-resolution subsurface conductivity imaging methods would have benefits far beyond the petroleum application. Such techniques would be very useful in environmental applications, mineral and geothermal exploration and for civil engineering applications.
Date: June 1, 1995
Creator: Lee, K.H.
Partner: UNT Libraries Government Documents Department

Telluric and D.C. Resistivity Techniques Applied to the Geophysical Investigation of Basin and Range Geothermal Systems, Part II: A Numberical Model Study of the Dipole-Dipole and Schlumberger Resistivity Methods

Description: This paper is a two-dimensional numerical model study and comparison of the polar dipole-dipole and Schlumberger resistivity arrays. A catalog of dipole-dipole and Schlumberger apparent resistivity pseudo-sections is presented. It is concluded that: for the Schlumberger array, data can be accurately interpreted only if the resistivity structure is horizontally layered, and conductive bodies having a depth of burial greater than their width are not observed; for the dipole-dipole array, complex anomaly patterns unrelated in appearance to the causative structure result from simple models, hence, a familiarity with model results is essential to interpretation of these data.
Date: June 1, 1977
Creator: Beyer, J.H.
Partner: UNT Libraries Government Documents Department

Proof of concept of moving thru casing resistivity apparatus. Annual report, October 1, 1990--September 30, 1991

Description: This is a continuing research effort into the new field of measuring the resistivity of geological formations from within cased wells. Original research objectives are summarized as follows: Additional data confirming the feasibility of technology is to be taken in a test well with the existing stophold-and-lock apparatus which is called the Through Casing Resistivity Apparatus (``TCRA``). the already existing TCRA will then be modified mechanically and new electronic components will be fabricated to test the concept of a moving apparatus called the Moving Through Casing Resistivity Apparatus (``MTCRA``); Additional data confirming the feasibility of the technology has been obtained with the existing stop-hold-and-lock Through Casing Resistivity Apparatus (``TCRA``). Data was obtained at the frequency of 1 Hz. The vertical spacing of each voltage measurement electrode pair was approximately 57 inches. The data proves the following: the technology works as generally outlined in various patents on the subject; the cement surrounding the well does not cause substantial measurement difficulties in formations having resistivities above 10 ohm-meters; and the data shows that thin beds can be resolved. The Moving Test Jig is a laboratory instrument which realistically simulates measurements to be done later downhole. It was designed, built, and has undergone many months of testing. The Moving Test Jig has electrodes which engage the interior of a rusty, piece of test casing. It is pulled through the rusty piece of test casing at various speeds of up to about 5 feet per minute. Electrical resistors on the outside of the casing allow conduction of A.C. current off the outside of the test pipe which can be directly measured. The Moving Test Jig then measures these currents independently with the technology developed under the DOE Grant. Agreement among these measurements means that we are properly measuring the parameters necessary to calculate the ...
Date: December 31, 1991
Creator: Vail, W.B.
Partner: UNT Libraries Government Documents Department

A resolution analysis of two geophysical imaging methods for characterizing and monitoring hydrologic conditions in the Vadose zone.

Description: This research project analyzed the resolution of two geophysical imaging techniques, electrical resistivity tomography (ERT) and cross-borehole ground penetrating radar (XBGPR), for monitoring subsurface flow and transport processes within the vadose zone. The study was based on petrophysical conversion of moisture contents and solute distributions obtained from unsaturated flow forward modeling. This modeling incorporated boundary conditions from a potable water and a salt tracer infiltration experiment performed at the Sandia-Tech Vadose Zone (STVZ) facility, and high-resolution spatial grids (6.25-cm spacing over a 1700-m domain) and incorporated hydraulic properties measured on samples collected from the STVZ. The analysis process involved petrophysical conversion of moisture content and solute concentration fields to geophysical property fields, forward geophysical modeling using the geophysical property fields to obtain synthetic geophysical data, and finally, inversion of this synthetic data. These geophysical property models were then compared to those derived from the conversion of the hydrologic forward modeling to provide an understanding of the resolution and limitations of the geophysical techniques.
Date: June 1, 2007
Creator: Brainard, James Robert; Hammond, Gary.; Alumbaugh, David L. (University of Wisconsin-Madison, Madison, WI) & La Brecque, D.J. (Multi-Phase Technologies, LLC, Sparks, NV)
Partner: UNT Libraries Government Documents Department

Resistivity Lows Near Paeroa Fault (TVZ, NZ) Caused by Topographic Effects

Description: Modeling of two-dimensional resistivity structures has been undertaken using a finite elements scheme that allows for accurate matching of the elevation of the ground surface. With this modeling program, interpretations were made of apparent resistivities measured with the multiple-source bipole-dipole array along several lines crossing the northern part of the Paeroa Fault. On a line crossing the Paeroa Scarp near its highest point, where the throw is 425 m, the topographic effect is inferred to cause the apparent resistivities to be lowered by about 40%, which accounts for the measured resistivity anomaly at the fault scarp. At the north-west of the Waikite-Puakohurea thermal region on another line, the topographic effect of a 100 m high ridge on Mt Waikorapa causes the apparent resistivities to be reduced by about 15%. This is insufficient to explain the measured low-resistivity anomaly. Thus, low-resistivity rock is inferred to underlie the site, suggesting that the thermal region extends about 1 km further to the north-westward than previously thought.
Date: January 1, 1995
Creator: Risk, G.F. & Bibby, H.M.
Partner: UNT Libraries Government Documents Department

Proof-of-concept of moving through casing resistivity apparatus. Final report, October 1, 1989--January 31, 1993

Description: ParaMagnetic Logging, Inc. (PML) demonstrated for the first time during 1990 in a Test Well located in Forth Worth, Texas that formation resistivity could be measured, in-principle, from within cased wells with the Through Casing Resistivity Tool (TCRT) designed and built by PML. Early results from this first instrument provided the impetus to investigate measurements methods to increase data acquisition rates and mechanical designs to improve vertical resolution which were implemented in the second experimental version of the TCRT. PML investigated the design requirements for a tool that could continuously move upward within a cased well. It was found that although such measurements can be done, various interfering signals, including those identified as due to the Triboelectric Effect, would mask the weak borehole casing signals if standard wirelines and components from the industry are utilized which limit the amount of electrical current delivered to the well. Extensive laboratory measurements were performed with the Moving Test Jig to investigate the properties of the Triboelectric Effect. Successful methods of measurement were devised to achieve acceptable performance objectives and to overcome problems with the Triboelectric Effect. One such method is called the Slider Method of Measurement.
Date: March 1, 1997
Creator: Vail, W.B. & Momii, S.T.
Partner: UNT Libraries Government Documents Department

Electrical and electromagnetic methods for reservoir description and process monitoring. Annual report, October 1, 1992--September 30, 1993

Description: It is well known that electrical conductivity of rock is closely related to the porosity, hydrologic permeability, saturation, and the type of fluid in it. These rock parameters play important roles in the development and production of hydrocarbon (petroleum and natural gas) resources. For these reasons, resistivity well logs have long been used by geologists and reservoir engineers in petroleum industries to map variations in pore fluid, to distinguish between rock types, and to determine completion intervals in wells. Reservoir simulation and process monitoring rely heavily on the physical characteristics of the reservoir model. At the beginning of FY-91 a coordinated electrical and electromagnetic (EM) geophysical research program for petroleum reservoir characterization and process monitoring was initiated. Parties involved in this program include Lawrence Berkeley Laboratory (LBL), Lawrence Livermore Laboratory (LLNL), Sandia National Laboratory (SNL), and University of California at Berkeley (UCB). The overall objectives of the program were: to integrate research funded by DOE for hydrocarbon recovery into a focused effort to demonstrate the technology in the shortest time with the least cost; to assure industry acceptance of the technology developed by having industry involvement in the planning, implementation, and funding of the research; to focus the research on real world problems that have the potential for solution in the near term with significant energy payoff. Specific research activities conducted have been in the following areas: (1) EM modeling development; (2) data interpretation methods development; (3) hardware and instrumentation development; (4) EOR and reservoir characterization; (5) controlled field experiments. The primary focus of these activities was in the development of reliable inversion and imaging schemes that could yield conductivity distributions from measured electrical and EM field data.
Date: July 1, 1995
Creator: Morrison, H.F.; Lee, K.H. & Becker, A.
Partner: UNT Libraries Government Documents Department

Inductive resistivity logging in steel-cased boreholes. SBIR Phase 2 progress report

Description: SBIR Phase 2 project 40145-97-I calls for the design and construction of a prototype inductive logging device to measure formation resistivity from within a steel-cased borehole. The SCIL (Steel Casing Induction Logger) tool is intended for reservoir characterization and process monitoring in an oil field environment. This report summarizes findings from the initial project period. In this phase, bench model measurements were made to test casing compensation schemes, numerical models were calculated to optimize the tool configuration and associated formation sensitivity and the preliminary design of the tool was completed. The bench tests constitute fundamental research on determining the characteristics of steel well casing and on developing means of separating the effects of the casing and the formation. This technology is crucial to the success of the project and significant progress has been made towards the goal of recovering the formation resistivity from inside the casing. Next, a series of sensitivity and tool configuration studies have been completed through partner Dr. David Alumbaugh at Sandia National Laboratories. These numerical results help to optimize the tool configuration and allow one to calculate the expected formation sensitivity. These models are preliminary to data interpretation software to be developed in the next project period. The initial hardware design of the tool has been completed, and ordering parts has begun for later manufacture and assembly. The tool, which is designed for maximum flexibility of deployment, will have a powerful transmitter, an array of three component sensors and sufficient dynamic range to operate in standard oil field steel-cased boreholes.
Date: July 1, 1999
Creator: Wilt, M.
Partner: UNT Libraries Government Documents Department

Reservoir characterization and process monitoring with EM methods. 1994 Annual report

Description: During the past five years at Lawrence Livermore National Laboratory (LLNL) the authors have applied the EM induction method to the problem of petroleum reservoir characterization and enhanced oil recovery (EOR) monitoring. The goal is to develop practical tools for determining the electrical resistivity distribution between boreholes at a useful scale for reservoir characterization. During FY94 the authors conducted their largest field test to date. They applied crosshole and surface-to-borehole EM techniques to reservoir characterization at the Los Hills No. 3 oil field making three sets of measurements during the initial phase of the steam drive.From these data they were able to determine the resistivity and configuration of the oil sands, between the observation wells, and provide an image of the subsurface resistivity changes due to the steam drive. They also conducted a waterflood experiment at the Richmond Field Station facility using the borehole-to-surface EM technique. For this test they injected a small quantity of saltwater, and applied the Em technique to monitor the progress of the injected plume. Data collection for this experiment is complete but the results are yet to be interpreted. Finally, a project to understand EM propagation through steel casing was initiated in 1994. The goals of the experiment are to determine the limits and applications for crosswell EM surveys through steel well casing.
Date: May 1, 1995
Creator: Wilt, M.
Partner: UNT Libraries Government Documents Department

New Mexico State University geothermal production well. Technical completion report, January 1, 1978-December 31, 1979

Description: The detailed technical specifications for the production well, the lithologic sample analysis, and a suite of geophysical logs, consisting of electrical resistivity, spontaneous potential, gamma ray and neutron, are presented. (MHR)
Date: January 1, 1981
Creator: Chaturvedi, L.
Partner: UNT Libraries Government Documents Department

Formation evaluation in liquid-dominated geothermal reservoirs

Description: Studies relative to some formation evaluation aspects of geothermal reservoirs are reported. The particular reservoirs considered were the liquid dominated type with a lithology of the sedimentary nature. Specific problems of interest included the resistivity behavior of brines and rocks at elevated temperatures and studies on the feasibility of using the well log resistivity data to obtain estimates of reservoir permeability. Several papers summarizing the results of these studies were presented at various technical meetings for rapid dissemination of the results to potential users. These papers together with a summary of data most recently generated are included. A brief review of the research findings precedes the technical papers. Separate abstracts were prepared for four papers. Five papers were abstracted previously for EDB.
Date: April 1, 1981
Creator: Ershaghi, I.; Dougherty, E.E. & Handy, L.L.
Partner: UNT Libraries Government Documents Department

Natural-gas-hydrate deposits: a review of in-situ properties

Description: The Los Alamos hydrate project has concentrated on: evaluating techniques to produce gas from hydrate deposits to determine critical reservoir and production variables; predicting physical properties of hydrate-containing sediments both for their effects on production models and to allow us to develop geophysical exploration and reservoir characterization techniques; and measuring properties of synthetic hydrate cores in the laboratory. Exploration techniques can help assess the size of potential hydrate deposits and determine which production techniques are appropriate for particular deposits. So little is known about the physical properties of hydrate deposits that it is difficult to develop geophysical techniques to locate or characterize them; but, because of the strong similarity between hydrates and ice, empirical relationships between ice composition and seismic velocity, electrical resistivity, density, and heat capacity that have been established for frozen rocks may be used to estimate the physical properties of hydrate deposits. Resistivities of laboratory permafrost samples are shown to follow a variation of Archie's equation. Both the resistivities and seismic velocities are functions of the unfrozen water content (Sw); however, resistivities are more sensitive to changes in Sw, varying by as much as three orders of magnitude, which may allow the use of electrical resistivity measurements to estimte the amount of hydrate in place. We estimated Sw, assuming that the dissolved salt in the pore water is concentrated as a brine phase as the hydrates form, and the brine content as a function of depth, assuming several temperature gradients and pore water salinities. Hydrate-bearing zones are characterized by high seismic velocities and electrical resistivities compared to unfrozen sediments or permafrost zones.
Date: January 1, 1982
Creator: Halleck, P.M.; Pearson, C.; McGuire, P.L.; Hermes, R. & Mathews, M.
Partner: UNT Libraries Government Documents Department

FORTRAN algorithm for correcting normal resistivity logs for borehold diameter and mud resistivity

Description: The FORTRAN algorithm described was developed for applying corrections to normal resistivity logs of any electrode spacing for the effects of drilling mud of known resistivity in boreholes of variable diameter. The corrections are based on Schlumberger departure curves that are applicable to normal logs made with a standard Schlumberger electric logging probe with an electrode diameter of 8.5 cm (3.35 in). The FORTRAN algorithm has been generalized to accommodate logs made with other probes with different electrode diameters. Two simplifying assumptions used by Schlumberger in developing the departure curves also apply to the algorithm: (1) bed thickness is assumed to be infinite (at least 10 times larger than the electrode spacing), and (2) invasion of drilling mud into the formation is assumed to be negligible.
Date: unknown
Creator: Scott, J.H.
Partner: UNT Libraries Government Documents Department

Topical report on subsurface fracture mapping from geothermal wellbores. Phase I. Pulsed radar techniques. Phase II. Conventional logging methods. Phase III. Magnetic borehole ranging

Description: To advance the state-of-the-art in Hot Dry Rock technology, an evaluation is made of (i) the use of radar to map far-field fractures, (ii) the use of more than twenty different conventional well logging tools to map borehole-fracture intercepts, and (iii) the use of magnetic dipole ranging to determine the relative positions of the injection well and the production well within the fractured zone. It is found that according to calculations, VHF backscatter radar has the potential for mapping fractures within a distance of 50 +- 20 meters from the wellbore. A new technique for improving fracture identification is presented. Analyses of extant data indicate that when used synergistically the (1) caliper, (2) resistivity dipmeter, (3) televiewer, (4) television, (5) impression packer, and (6) acoustic transmission are useful for mapping borehole-fracture intercepts. Improvements in both data interpretation techniques and high temperature operation are required. The surveying of one borehole from another appears feasible at ranges of up to 200 to 500 meters by using a low frequency magnetic field generated by a moderately strong dipole source (a solenoid) located in one borehole, a sensitive B field detector that traverses part of the second borehole, narrow band filtering, and special data inversion techniques.
Date: September 1, 1980
Creator: Hartenbaum, B.A. & Rawson, G.
Partner: UNT Libraries Government Documents Department

Results of investigation at the Ahuachapan Geothermal Field, El Salvador

Description: The Ahuachapan Geothermal Field (AGF) is a 95 megawatt geothemal-sourced power-plant operated by the Comision Ejecutiva Hidroelectrica del Rio Lempa (CEL) of El Salvador. During the past decade, as part of an effort to increase in situ thermal reserves in order to realize the full generation capacity of the AGF, extensive surface geophysical coverage has been obtained over the AGF and the prospective Chipilapa area to the east. The geophysical surveys were performed to determine physical property characteristics of the known reservoir and then to search for similar characteristics in the Chipilapa area. A secondary objective was to evaluate the surface recharge area in the highlands to the south of the AGF. The principal surface electrical geophysical methods used during this period were DC resistivity and magnetotellurics. Three available data sets have been reinterpreted using drillhole control to help form geophysical models of the area. The geophysical models are compared with the geologic interpretations.
Date: April 1, 1990
Creator: Fink, J.B. (HydroGeophysics, Tucson, AZ (United States))
Partner: UNT Libraries Government Documents Department

Lithology and hydrothermal alteration determination from well logs for the Cerro Prieto Wells, Mexico

Description: The purpose of this study is to examine the characteristics of geophysical well logs against the sand-shale series of the sedimentary column of the Cerro Prieto Geothermal Field, Mexico. The study shows that the changes in mineralogy of the rocks because of hydrothermal alteration are not easily detectable on the existing logs. However, if the behavior of clay minerals alone is monitored, the onset of the hydrothermally altered zones may be estimated from the well logs. The effective concentration of clay-exchange cations, Q/sub v/, is computed using the data available from conventional well logs. Zones indicating the disappearance of low-temperature clays are considered hydrothermally altered formations with moderate to high-permeability and temperature, and suitable for completion purposes.
Date: October 1, 1981
Creator: Ershaghi, I.; Ghaemian, S. & Abdassah, D.
Partner: UNT Libraries Government Documents Department

Interpretation of well log data from four drill holes at Roosevelt Hot Springs KGRA

Description: Well logs from four drill holes, Utah State Geothermal Wells 14-2, 52-21 and 72-16 and Geothermal Power Corporation's thermal gradient hole GPC-15 have been digitized, plotted and studied. This study had three objectives: (1) to present the well log data in a convenient format for easy study, (2) to determine the nature of the geothermal reservoir rock and fluid properties, and (3) to make some inference on fluid entry locations in the boreholes and their effect on heat flow. The temperature logs and gradients computed from these logs have been used to examine heat flow in the vicinity of the four drill holes. Assumed and calculated thermal conductivities have been used in the analyses, 4 mcal/cm /sup 0/C sec for the alluvium and 7 mcal/cm /sup 0/C sec for the crystalline rocks. The data indicate that 14-2 and 72-16 reside in a dominantly convective heat flow environment, whereas GPC-15 and 52-21 reside in a dominantly conductive heat flow environment. The convective regions are believed to be fracture controlled and only portions of each hole reside totally in a convective region; in each case it is the upper bedrock portion of the hole. In every case the alluvium or upper portion of the alluvium acts as a thermal blanket over the system. Maximum heat flow among the holes, 40 ..mu.. cal/cm/sup 2/ sec, occurs in the vicinity of 72-16 and the lowest heat flow, 4 ..mu.. cal/cm/sup 2/ sec, in the vicinity of GPC-15. (MHR)
Date: December 1, 1979
Creator: Glenn, W.E. & Hulen, J.B.
Partner: UNT Libraries Government Documents Department

Sonic and resistivity measurements on Berea sandstone containing tetrahydrofuran hydrates: a possible analogue to natural-gas-hydrate deposits. [Tetrahydrofuran hydrates]

Description: Deposits of natural gas hydrates exist in arctic sedimentary basins and in marine sediments on continental slopes and rises. However, the physical properties of such sediments are largely unknown. In this paper, we report laboratory sonic and resistivity measurements on Berea sandstone cores saturated with a stoichiometric mixture of tetrahydrofuran (THF) and water. We used THF as the guest species rather than methane or propane gas because THF can be mixed with water to form a solution containing proportions of the proper stoichiometric THF and water. Because neither methane nor propane is soluble in water, mixing the guest species with water sufficiently to form solid hydrate is difficult. Because THF solutions form hydrates readily at atmospheric pressure it is an excellent experimental analogue to natural gas hydrates. Hydrate formation increased the sonic P-wave velocities from a room temperature value of 2.5 km/s to 4.5 km/s at -5/sup 0/C when the pores were nearly filled with hydrates. Lowering the temperature below -5/sup 0/C did not appreciably change the velocity however. In contrast, the electrical resistivity increases nearly two orders of magnitude upon hydrate formation and continues to increase more slowly as the temperature is further decreased. In all cases the resistivities are nearly frequency independent to 30 kHz and the loss tangents are high, always greater than 5. The dielectric loss shows a linear decrease with frequency suggesting that ionic conduction through a brine phase dominates at all frequencies, even when the pores are nearly filled with hydrates. We find that the resistivities are strongly a function of the dissolved salt content of the pore water. Pore water salinity also influences the sonic velocity, but this effect is much smaller and only important near the hydrate formation temperature.
Date: January 1, 1983
Creator: Pearson, C.; Murphy, J.; Halleck, P.; Hermes, R. & Mathews, M.
Partner: UNT Libraries Government Documents Department

Study of the geothermal production potential in the Williston Basin, North Dakota

Description: Preliminary studies of geothermal production potential for the North Dakota portion of the Williston Basin have been carried out. Reservoir data such as formation depth, subsurface temperatures, and water quality were reviewed for geothermal brine production predictions. This study, in addition, provides important information about net pay thickness, porosity, volume of geothermal water available, and productivity index for future geothermal direct-use development. Preliminary results show that the Inyan Kara Formation of the Dakota Group is the most favorable geothermal resource in terms of water quality and productivity. The Madison, Duperow, and Red River Formations are deeper formations but because of their low permeability and great depth, the potential flow rates from these three formations are considerably less than those of the Inyan Kara Formation. Also, poor water quality and low porosity will make those formations less favorable for geothermal direct-use development.
Date: September 10, 1991
Creator: Chu, Min H.
Partner: UNT Libraries Government Documents Department

Analysis of geophysical logs from the Hawaii geothermal project well

Description: A 6445-foot test well was completed on April 27, 1976 in the Puna Area of Hawaii as part of an extensive project to investigate a geothermal reservoir for energy production. Because bottom hole temperatures exceeded 300/sup 0/C, it was possible to run geophysical logs in the upper 3500 feet only. Study of conventional and induction resistivity, self potential, neutron, gamma ray, caliper, temperature, temperature differential and drilling rate logs show that porosity, permeability and fluid flow are qualitatively identified on the logs. Lithologic logs of sample cuttings taken at five- to ten-foot intervals (together with cores taken at approximately 700-foot intervals) substantiate preliminary findings of the porous and permeable zones. Although the logs investigated are above many of the zones of production, new information was obtained about the in-situ nature of permeability in Hawaiian basalts.
Date: September 1, 1978
Creator: Rudman, A.J.
Partner: UNT Libraries Government Documents Department

Dipole-dipole resistivity survey of a portion of the Coso Hot Springs KGRA, Inyo County, California

Description: A detailed electrical resistivity survey of 54 line-km was completed at the Coso Hot Springs KGRA in September 1977. This survey has defined a bedrock resistivity low at least 4 sq mi (10 sq km) in extent associated with the geothermal system at Coso. The boundaries of this low are generally well defined to the north and west but not as well to the south where an approximate southern limit has been determined. The bedrock resistivity low merges with an observed resistivity low over gravel fill east of Coso Hot Springs. A complex horizontal and vertical resistivity structure of the surveyed area has been defined which precludes the use of layered-earth or two-dimensional interpretive models for much of the surveyed area. In general the survey data indicate that a 10 to 20 ohm-meter zone extends from near surface to a depth greater than 750 meters within the geothermal system. This zone is bordered to the north and west by bedrock resistivities greater than 200 ohm-meters and to the south by bedrock resistivities greater than 50 ohm-meters. A combination of observed increases in: (1) fracture density (higher permeability), (2) alteration (high clay content), and (3) temperatures (higher dissolved solid content of ground water) within the bedrock low explain its presence.
Date: May 1, 1978
Creator: Fox, R. C.
Partner: UNT Libraries Government Documents Department

Applications of geothermal well log data for evaluation of reservoir potential

Description: A great many geothermal reservoirs are naturally fractured stems with porosity supplied by both the macroscopic fracture system and by dispersed intergranular or vuggy porosity. Flow properties, the use of log data for well test interpretation in such systems, and the log derivable parameters that may be of most value for evaluation are discussed here. Parameters for describing behavior of two-phase geothermal systems are also mentioned. Determination of reservoir dimensions is another important problem aggravated in geothermal resource evaluation by our limited knowledge of the geophysics of geothermal systems. The use of resistivity log data to deduce constraints on the inversion of surface resistivity data is examined. Potentially valuable applications of resistivity log data in deducing reservoir dimensions and reaching decisions on exploratory drilling are indicated.
Date: March 1, 1981
Creator: Rigby, F.A.
Partner: UNT Libraries Government Documents Department