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A comprehensive study of fracture patterns and densities in the Geysers geothermal reservoir using microearthquake shear-wave splitting tomography. [Quarterly progress report 03/16/1998 - 06/15/1998]

Description: We completed the process of identifying shear-wave splitting in the Geyser area. A total of 2700 observations were recorded with about 1700 observations from the 1988 data and about 1000 observations from 1994. Fast polarization direction map in Figure 1 shows that most of the stations in the Geyser area display consistent direction throughout the main field, between 0{degree} azimuth to 40{degree} azimuth. Some exemptions to the consistent crack alignment (fast polarization direction) can be seen in stations 9 and station 3, and also in stations 13 and 14 outside the field. Since the stations are in boreholes it is possible that some of the station orientations, calculated using P-wave arrivals from located events, are erroneous. If we treat measurements of polarization direction as a statistical process, same as deep of layer measurement, we can say that in the small area of the station we have aligned cracks. Figures 2 and 3 show results of the crack density inversion assuming regional crack azimuth of 20{degree}. Almost 2400 raypaths were used to perform this tomographic inversion. There is weak dependency of the results on the regional crack direction, but the main areas of high and low crack density are the same. The changes are mainly in the size of the anomalies. Since the amplitudes of those anomalies depend mainly on the damping parameter we use in the inversion, exact regional crack direction is not a critical parameter of the inversion. The map in figure 2 and cross-sections in Figure 3 show two areas of high crack density at the top 1 km one at station 8 and the other between stations 6 and 5. At greater depth of 1 to 2 km those two area converge to one high crack density anomaly between stations 3, 4, 11, and 10.
Date: March 17, 1999
Creator: Malin, P.E. & Shalev, E.
Partner: UNT Libraries Government Documents Department

A comprehensive study of fracture patterns and densities in the Geysers geothermal reservoir using microearthquake shear-wave splitting tomography [Quarterly progress report 06/16/1998 - 09/15/1998]

Description: We completed the process of locating events and identifying shear-wave splitting in the mammoth area. A total of 2250 split shear wave observations were recorded in the four month period that our network was in place. Fast polarization direction map in Figure 1 shows that most of the stations in the mammoth area display consistent direction throughout the main field, between 300{degree} azimuth to 0{degree} azimuth. Some exemptions to the consistent crack alignment (fast polarization direction) can be seen in station M19, and some stations display inconsistent trend as can be observed in stations M25, M18, and M07. It is possible that station M19 was misaligned during installment. Figure 2 shows the cumulative rose diagram for all observations with a clear preferred direction. Figure 3 also shows that most of the observations of fast split shear wave are in the same direction and that those observation are distributed throughout the target area. If we treat measurements of polarization direction as a statistical process, same as deep of layer measurement, we can say that in the small area of the station we have aligned cracks. Figures 4 and 5 show results of the crack density inversion assuming regional crack azimuth of 340{degree}. Almost 2000 raypaths were used to perform this tomographic inversion. There is weak dependency of the results on the regional crack direction, but the main areas of high and low crack density are the same. The changes are mainly in the size of the anomalies. Since the amplitudes of those anomalies depend mainly on the damping parameter we use in the inversion, exact regional crack direction is not a critical parameter of the inversion. The map in figure 4 and cross-sections in Figure 5 show two areas of high crack density: one northeast of the Casa Diablo area at ...
Date: March 26, 1999
Creator: Malin, P.E. & Shalev, E.
Partner: UNT Libraries Government Documents Department

Hydrologic characterization of four cores from the Geysers Coring Project

Description: Results of hydrologic tests on 4 representative core plugs from Geysers Coring Project drill hole SB-15-D were related to mineralogy and texture. Permeability measurements were made on 3 plugs from caprock and one plug from the steam reservoir. Late-stage microfractures present in 2 of the plugs contributed to greater permeability, but the values for the 2 other plugs indicate a typical matrix permeability of 1 to 2 {times} 10{sup {minus}21}m{sup 2}. Klinkenberg slip factor b for these plugs is generally consistent with the inverse relation between slip factor and permeability observed by Jones (1972) for plugs of much more permeable material. The caprock and reservoir samples are nearly identical metagraywackes with slight mineralogical differences which appear to have little effect on hydrology. The late stage microfractures are suspected of being artifacts. The capillary pressure curves for 3 cores are fit by power-law relations which can be used to estimate relative permeability curves for the matrix rocks.
Date: January 1, 1996
Creator: Persoff, P. & Hulen, J.B.
Partner: UNT Libraries Government Documents Department

Public Workshop, Staff Technical Meeting with Applicant on Geysers Unit 17

Description: The overall purpose of this meeting is to discuss the report that was sent to PG and E on February 1st discussing Geysers 17. The Commission has reviewed all of the existing data, the majority of the existing data that have gone through both Lake County and through the CPUC regarding 17, looked at the existing data to see what, if any, additional would be required to file and expeditiously process a Notice of Intention on Geysers Unit 17.
Date: February 21, 1978
Creator: Schiller, Wendy E.
Partner: UNT Libraries Government Documents Department

X-ray tomography of preserved samples from the Geysers scientific corehole

Description: Approximately 800 ft. of continuous core was recovered from borehole SB-15 D (on unit 15, near the site of the abandoned Geysers Resort) during a recently completed drilling operation. Sections of this core were collected at 50 ft intervals for subsequent examination as drilling proceeded. Five foot sections were not removed at the drill site, but were sealed in the innermost sleeve of a triple tube coring system to minimize drying and disturbance of the core. All cores remained sealed and were radiographed within 72 hours of drilling: the five foot core from near 1400 ft. was scanned within 18 hours of drilling. A third generation x-ray scanner, which uses high energy radiation to penetrate the aluminum sleeve and 3.5 inch cores, was used to make preliminary radiographs and to collect multiple views of the sample as the core is rotated in front of the beam. True three dimensional tomographs are then reconstructed from the data. The images have a spatial resolution of approximately 140 micrometers and can resolve contrast differences of 0.2%. The tomographs clearly show differences in lithology with depth in the reservoir. Partially filled fractures, vein selvage and vuggy porosity are all evident in parts of the core. A principle goal is to determine the fluid content of the reservoir. Important questions to investigate include water loss during core recovery, infiltration of drilling fluid, and the heterogeneous distribution of pore fluid. Images show that radial gradients in x-ray attenuation commonly occur in jacketed cores. Regions of excess attenuation extend about halfway into the 3.5 in. core, and are probably caused by mud invasion induced by capillarity of the small scale porosity of the graywacke matrix. X-ray measurements will be coordinated with other independent measurements of fluid content underway in separate studies, particularly NMR spectroscopy of frozen `pressure ...
Date: January 23, 1995
Creator: Bonner, B.P.; Roberts, J.J.; Schneberk, D.J.; Marsh, A.; Ruddle, C. & Updike, E.
Partner: UNT Libraries Government Documents Department

Heat flow and hot dry rock geothermal resources of the Clearlake Region, northern California

Description: The Geysers-Clear Lake geothermal anomaly is an area of high heat flow in northern California. The anomaly is caused by abnormally high heat flows generated by asthenospheric uplift and basaltic magmatic underplating at a slabless window created by passage of the Mendocino Triple Junction. The Clear Lake volcanic field is underlain by magmatic igneous bodies in the form of a stack of sill-form intrusions with silicic bodies generally at the top and basic magmas at the bottom. The tabular shape and wide areal extent of the heat sources results in linear temperature gradients and near-horizontal isotherms in a broad region at the center of the geothermal anomaly. The Hot Dry Rock (HDR) portion of The Geysers-Clear Lake geothermal field is that part of the geothermal anomaly that is external to the steamfield, bounded by geothermal gradients of 167 mW/m2 (4 heat flow units-hfu) and 335 mW/m2 (8 hfu). The HDR resources, to a depth of 5 km, were estimated by piece-wise linear summation based on a sketch map of the heat flow. Approximately, the geothermal {open_quotes}accessible resource base{close_quotes} (Qa) is 1.68E+21 J; the {open_quotes}HDR resource base{close_quotes} (Qha) is 1.39E+21 J; and the {open_quotes}HDR power production resource{close_quotes} (Qhp) is 1.01E+21 J. The HDR power production resource (Qhp) is equivalent to 2.78E+ 11 Mwht (megawatt hours thermal), or 1.72E+11 bbls of oil.
Date: August 1, 1996
Creator: Burns, K.L.
Partner: UNT Libraries Government Documents Department

A comprehensive study of fracture patterns and densities in the Geysers geothermal reservoir using microearthquake shear-wave splitting tomography. Quarterly report for Sep-Dec 1998

Description: We start organizing the computer programs needed for crack density inversion into an easy to follow scripts. These programs were collection of bits and pieces from many sources and we want to organize those separate programs into coherent product. We also gave a presentation (enclosed) in the Twenty-Fourth Workshop on Geothermal Reservoir Engineering in Stanford University on our Geyser and Mammoth results.
Date: March 31, 1999
Creator: Malin, Peter E. & Shalev, Eylon
Partner: UNT Libraries Government Documents Department

Geothermal regimes of the Clearlake region, northern California

Description: The first commercial production of power from geothermal energy, at The Geysers steamfield in northern California in June 1960, was a triumph for the geothermal exploration industry. Before and since, there has been a search for further sources of commercial geothermal power in The Geysers--Clear Lake geothermal area surrounding The Geysers. As with all exploration programs, these were driven by models. The models in this case were of geothermal regimes, that is, the geometric distribution of temperature and permeability at depth, and estimates of the physical conditions in subsurface fluids. Studies in microseismicity and heat flow, did yield geophysical information relevant to active geothermal systems. Studies in stable-element geochemistry found hiatuses or divides at the Stoney Creek Fault and at the Collayomi Fault. In the region between the two faults, early speculation as to the presence of steamfields was disproved from the geochemical data, and the potential existence of hot-water systems was predicted. Studies in isotope geochemistry found the region was characterized by an isotope mixing trend. The combined geochemical data have negative implications for the existence of extensive hydrothermal systems and imply that fluids of deep origin are confined to small, localized systems adjacent to faults that act as conduits. There are also shallow hot-water aquifers. Outside fault-localized systems and hot-water aquifers, the area is an expanse of impermeable rock. The extraction of energy from the impermeable rock will require the development and application of new methods of reservoir creation and heat extraction such as hot dry rock technology.
Date: June 1, 1998
Creator: Amador, M.; Burns, K.L. & Potter, R.M.
Partner: UNT Libraries Government Documents Department

Vertical arrays for fracture mapping in geothermal systems

Description: In collaboration with UNOCAL Geothermal Operations, Los Alamos National Laboratory assessed the feasibility of using vertical arrays of borehole seismic sensors for mapping of microseismicity in The Geysers geothermal field. Seismicity which arises from minute displacements along fracture or fault surfaces has been shown in studies of seismically active oil reservoirs to be useful in identifying fractures affected by and possibly contributing to production. Use of retrievable borehole seismic packages at The Geysers was found to reduce the threshold for detection of microearthquakes by an estimated 2--3 orders of magnitude in comparison to surface-based sensors. These studies led to the design, materials selection, fabrication, and installation of a permanent array of geophones intended for long term seismic monitoring and mapping of fractures in the vicinity of the array at The Geysers.
Date: December 1, 1998
Creator: Albright, J.N.; Rutledge, J.T.; Fairbanks, T.D.; Thomson, J.C. & Stevenson, M.A.
Partner: UNT Libraries Government Documents Department

Reservoir technology research at the INEL

Description: Reservoir engineering research at INEL was aimed at developing a better understanding of The Geysers and developing better tools with which to study flow in fractured geothermal reservoirs in general. Two specific topics were studies in the last year: matrix fracture interactions and decline curve analysis. A third project, revisiting the behavior of the `high-temperature reservoir` (HTR), was started near the end of 1995. These projects are being conducted in collaboration with other researchers and/or private industry. For example, our HTR studies are motivated in part because of new isotopic analyses conducted elsewhere (Walters et al., in preparation). The ultimate goal of these projects is to improve predictive capabilities and reservoir management practices and to extend the commercial life of The Geysers. In addition to conducting engineering research for the Reservoir Technology Program, INEL also continued to assist the Geothermal Technology Organization (GTO) with the development and execution of cooperative research projects. In support of the overall mission of the Reservoir Technology program, INEL also entered into a broad program of subcontracts with industrial groups and universities. These programs support the Reservoir Technology mission by providing support for research topics considered particularly important by the geothermal industry. The GTO projects are summarized below.
Date: May 1, 1996
Creator: Renner, J. L.; Shook, G. M. & Faulder, D. D.
Partner: UNT Libraries Government Documents Department


Description: The large Thermal Landslide overlies the initial area of geothermal development at The Geysers. The landslide is waterbearing while the underlying Franciscan formation bedrock units are essentially non-waterbearing except where affected by hydrothermal alteration. Perched ground water moving through the landslide is heated prior to discharge as spring flow.
Date: January 22, 1985
Creator: Vantine, J.
Partner: UNT Libraries Government Documents Department

Seismic monitoring at the Geysers Geothermal Field

Description: This report summarizes the efforts of LBL to utilize MEQ data in reservoir definition as well as in evaluating its performance. Results of the study indicate that the velocity and attenuation variations correlate with the known geology of the field. At the NW Geysers, high velocity anomalies correspond to metagraywacke and greenstone units while low velocity anomalies seem to be associated with Franciscan melanges. Low Vp/Vs and high attenuation delineate the steam reservoir suggesting undersaturation of the reservoir rocks. Ongoing monitoring of Vp/Vs may be useful in tracking the expansion of the steam zone with time. Spatial and temporal patterns of seismicity exhibit compelling correlation with geothermal exploitation. Clusters of MEQs occur beneath active injection wells and appear to shift with changing injection activities. High resolution MEQ locations hold promise for inferring fluid flow paths, especially in tracking injectate. This study has demonstrated that continuous seismic monitoring may be useful as an active reservoir management tool.
Date: September 1, 1994
Creator: Romero, A. E. Jr.; Kirkpatrick, A.; Majer, E. L. & Peterson, J. E. Jr.
Partner: UNT Libraries Government Documents Department

Permeability-thickness determination from transient production response at the southeast geysers

Description: The Fetkovich production decline curve analysis method was extended for application to vapor-dominated geothermal reservoirs for the purpose of estimating the permeability-thickness product (kh) from the transient production response. The analytic dimensionless terms for pressure, production rate, decline rate, and decline time were derived for saturated steam using the real gas potential and customary geothermal production units of pounds-mass per hour. The derived terms were numerically validating using ``Geysers-line`` reservoir properties at initial water saturation of 0 and at permeabilities of 1, 10, and 100 mD. The production data for 48 wells in the Southeast Geysers were analyzed and the permeability-thickness products determined from the transient production response using the Fetkovich production decline type curve. The kh results were in very good agreement with the published range at the Southeast Geysers and show regions of high permeability-thickness.
Date: August 1, 1996
Creator: Faulder, D.D.
Partner: UNT Libraries Government Documents Department

Literature survey on cements for remediation of deformed casing in geothermal wells

Description: Brookhaven National Laboratory was requested to conduct a literature survey for the best available cement to use in the proposed casing patch as part of the Geothermal Drilling Organization (GDO) project on remediation of deformed casings. A total of 50 wells have been identified with deformed production casing in Unocal`s portion of The Geysers geothermal field. A procedure to address the casing deformation and avoid abandonment of these wells has been developed as described in the Geysers Deformed Casing Remediation Proposal. The proposed remediation procedure involves isolation of the zone of interest with an inflatable packer, milling the deformed casing and cementing a 7 inch diameter liner to extend approximately 100 ft above and 100 ft below the milled zone. During the milling operation it is possible that the original cement and surrounding formation may slough away. In order to specify a suitable cement formulation for the casing patch it is first necessary to identify and understand the deformation mechanism/s operating in The Geysers field. Subsequently, the required cement mechanical properties to withstand further deformation of the repaired system must be defined. From this information it can be determined whether available cement formulations meet these requirements. In addition to The Geysers, other geothermal fields are at possible risk of casing deformation due to subsidence, seismic activity, lateral and vertical formation movement or other processes. Therefore, the proposed remediation procedure may have applications in other fields.
Date: December 31, 1998
Creator: Allan, M.L. & Philippacopoulos, A.J.
Partner: UNT Libraries Government Documents Department

Decline curve analysis of vapor-dominated reservoirs

Description: Geothermal Program activities at the INEEL include a review of the transient and pseudosteady state behavior of production wells in vapor-dominated systems with a focus on The Geysers field. The complicated history of development, infill drilling, injection, and declining turbine inlet pressures makes this field an ideal study area to test new techniques. The production response of a well can be divided into two distinct periods: transient flow followed by pseudo-steady state (depletion). The transient period can be analyzed using analytic equations, while the pseudo-steady state period is analyzed using empirical relationships. Yet by reviewing both periods, a great deal of insight can be gained about the well and reservoir. An example is presented where this approach is used to determine the permeability thickness product, kh, injection and production interference, and estimate the empirical Arps decline parameter b. When the production data is reinitialized (as may be required by interference effects), the kh determined from the new transient period is repeatable. This information can be used for well diagnostics, quantification of injection benefits, and the empirical estimation of remaining steam reserves.
Date: May 1, 1997
Creator: Faulder, D.D.
Partner: UNT Libraries Government Documents Department

Microearthquake source mechanism studies at the Geysers geothermal field

Description: In this paper the authors discuss moment tensors obtained from inversion of MEQ waveform data recorded at the Southeast (SE) and Northwest (NW) Geysers geothermal areas by the high-resolution seismic networks operated by Lawrence Berkeley National Laboratory (Berkeley Lab) and the Coldwater Creek Geothermal Company (now CCPA). The network in the SE Geysers consists of 13 high-frequency (4.5 Hz), digital (480 samples), three-component, telemetered stations deployed on the surface in portions of the Calpine, Unocal-NEC-Thermal (U-N-T), and Northern California Power Agency (NCPA) leases. The network in the NW Geysers is a 16-station borehole array of three-component geophones (4.5 Hz), digital at 400 samples/sec, and telemetered to a central site. One of the main objectives of Berkeley Lab`s program at the Geysers is to assess the utility of MEQ monitoring as a reservoir management tool. Discrimination of the mechanisms of these events may aid in the interpretation of MEQ occurrence patterns and their significance to reservoir processes and conditions of interest to reservoir managers. Better understanding of the types of failure deduced from source mechanism studies, and their relations to production parameters, should also lead to a better understanding of the effects of injection and withdrawal.
Date: April 1, 1996
Creator: Kirkpatrick, A.; Romero, A. Jr.; Peterson, J. Jr.; Johnson, L. & Majer, E.
Partner: UNT Libraries Government Documents Department

Volatility of HCl and the thermodynamics of brines during brine dryout

Description: Laboratory measurements of liquid-vapor partitioning (volatility) of chlorides from brines to steam can be used to indicate the potential for corrosion problems in geothermal systems. Measurements of volatilities of solutes in chloride brines have established a possible mechanism for the production of high-chloride steam from slightly acidic high temperature brines. Questions concerning the fate of NaCl in the steam production process have been addressed through extensive measurements of its volatility from brines ranging in concentration from dilute solutions to halite saturation. Recent measurements of chloride partitioning to steam over brines in contact with Geysers rock samples are consistent with our concept of the process for production of high-chloride steam.
Date: April 1, 1997
Creator: Simonson, J.M. & Palmer, D.A.
Partner: UNT Libraries Government Documents Department

Relating x-ray attenuation measurements to water content and distribution in SB-15D core

Description: Making improved estimates of the water content of The Geysers reservoir is fundamental to efficient and economic long term production of steam power from the resource. A series of coordinated physical properties measurements form core recovered from the SB-15D, reported in this volume in a series of papers, have been made to better understand water storage and to relate water content and distribution to observable geophysical properties such as electrical conductivity and seismic velocities. A principal objective here is to report new interpretations of x-ray scans made within 72 hours of core recovery from SB-15D, which suggest, taking advantage of preliminary measurements of capillary suction for metagraywacke, that water content was low in much of the preserved core.
Date: September 30, 1996
Creator: Bonner, B.P.; Roberts, J.J. & Schneberk, D.J
Partner: UNT Libraries Government Documents Department

Southeast geysers effluent pipeline project. Final report

Description: The project concept originated in 1990 with the convergence of two problems: (1) a need for augmented injection to mitigate declining reservoir productivity at the Geysers; and (2) a need for a new method of wastewater disposal for Lake County communities near the The Geysers. A public/private partnership of Geysers operators and the Lake County Sanitation District (LACOSAN) was formed in 1991 to conduct a series of engineering, environmental, and financing studies of transporting treated wastewater effluent from the communities to the southeast portion of The Geysers via a 29-mile pipeline. By 1994, these evaluations concluded that the concept was feasible and the stakeholders proceeded to formally develop the project, including pipeline and associated facilities design; preparation of an environmental impact statement; negotiation of construction and operating agreements; and assembly of $45 million in construction funding from the stakeholders, and from state and federal agencies with related program goals. The project development process culminated in the system`s dedication on October 16, 1997. As of this writing, all project components have been constructed or installed, successfully tested in compliance with design specifications, and are operating satisfactorily.
Date: January 15, 1998
Creator: Dellinger, M.
Partner: UNT Libraries Government Documents Department

Induced seismicity. Final report

Description: The objective of this project has been to develop a fundamental understanding of seismicity associated with energy production. Earthquakes are known to be associated with oil, gas, and geothermal energy production. The intent is to develop physical models that predict when seismicity is likely to occur, and to determine to what extent these earthquakes can be used to infer conditions within energy reservoirs. Early work focused on earthquakes induced by oil and gas extraction. Just completed research has addressed earthquakes within geothermal fields, such as The Geysers in northern California, as well as the interactions of dilatancy, friction, and shear heating, on the generation of earthquakes. The former has involved modeling thermo- and poro-elastic effects of geothermal production and water injection. Global Positioning System (GPS) receivers are used to measure deformation associated with geothermal activity, and these measurements along with seismic data are used to test and constrain thermo-mechanical models.
Date: September 18, 1997
Creator: Segall, P.
Partner: UNT Libraries Government Documents Department

Water adsorption at high temperature on core samples from The Geysers geothermal field

Description: The quantity of water retained by rock samples taken from three wells located in The Geysers geothermal reservoir, California, was measured at 150, 200, and 250 C as a function of pressure in the range 0.00 {le} p/p{sub 0} {le} 0.98, where p{sub 0} is the saturated water vapor pressure. Both adsorption (increasing pressure) and desorption (decreasing pressure) runs were made in order to investigate the nature and the extent of the hysteresis. Additionally, low temperature gas adsorption analyses were performed on the same rock samples. Nitrogen or krypton adsorption and desorption isotherms at 77 K were used to obtain BET specific surface areas, pore volumes and their distributions with respect to pore sizes. Mercury intrusion porosimetry was also used to obtain similar information extending to very large pores (macropores). A qualitative correlation was found between the surface properties obtained from nitrogen adsorption and the mineralogical and petrological characteristics of the solids. However, there is in general no proportionality between BET specific surface areas and the capacity of the rocks for water adsorption at high temperatures. The results indicate that multilayer adsorption rather than capillary condensation is the dominant water storage mechanism at high temperatures.
Date: June 1, 1998
Creator: Gruszkiewicz, M.S.; Horita, J.; Simonson, J.M. & Mesmer, R.E.
Partner: UNT Libraries Government Documents Department