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Analysis of cause and mechanism for injection-induced seismicityat the Geysers Geothermal Field, California

Description: We analyzed relative contributions to the cause andmechanism of injection-induced seismicity at The Geysers geothermalfield, California, using coupled thermal-hydrological-mechanicalmodeling. Our analysis shows that the most important cause forinjection-induced seismicity is injection-induced cooling and associatedthermal-elastic shrinkage that changes the stress state in such a waythat mechanical failure and seismicity can be induced. Specifically, thecooling shrinkage results in unloading and associated loss of shearstrength in critically shear-stressed fractures, which are thenreactivated. Thus, our analysis shows that cooling-induced shear slipalong fractures is the dominant mechanism of injection-induced seismicityat The Geysers.
Date: June 14, 2007
Creator: Rutqvist, Jonny & Oldenburg, Curtis
Partner: UNT Libraries Government Documents Department

Research in the Geysers-Clear Lake Geothermal Area, Northern California

Description: From abstract: The Geysers-Clear Lake geothermal area lies within the central belt of the Franciscan assemblage in northern California. The structure of this terrane is characterized by northeast-dipping imbricate thrust slices that have been warped and cut by steeply dipping strike-slip and normal faults. Introduction of magma into the crust beneath the Geysers-Clear Lake area can be related to eastsoutheast extension accompanying northward propagation of the San Andreas transform system between the Clear Lake region and Cape Mendocino within the last 3 million years. The initiation of strike-slip faulting during this time terminated subduction of elements of the Farallon plate beneath North America as strike-slip motion was taken up along the Pacific-North American plate boundary. The mechanism for magma generation appears to require a heat source in the mantle that mixed mantle-derived melts with various crustal rocks. These crustal rocks may have included the Franciscan central and coastal belts, ophiolite, Great Valley sequence, and possibly middle and late Tertiary rocks subducted before initiation of strike-slip faulting.
Date: 1981
Creator: McLaughlin, Robert J. & Donnelly-Nolan, Julie M.
Partner: UNT Libraries Government Documents Department

Integrated modeling and field study of potential mechanisms forinduced seismicity at The Geysers Goethermal Field, California

Description: In this paper, we present progress made in a study aimed atincreasing the understanding of the relative contributions of differentmechanisms that may be causing the seismicity occurring at The Geysersgeothermal field, California. The approach we take is to integrate: (1)coupled reservoir geomechanical numerical modeling, (2) data fromrecently upgraded and expanded NCPA/Calpine/LBNL seismic arrays, and (3)tens of years of archival InSAR data from monthly satellite passes. Wehave conducted a coupled reservoir geomechanical analysis to studypotential mechanisms induced by steam production. Our simulation resultscorroborate co-locations of hypocenter field observations of inducedseismicity and their correlation with steam production as reported in theliterature. Seismic and InSAR data are being collected and processed foruse in constraining the coupled reservoir geomechanicalmodel.
Date: June 7, 2006
Creator: Rutqvist, Jonny; Majer, Ernie; Oldenburg, Curt; Peterson, John & Vasco, Don
Partner: UNT Libraries Government Documents Department

Southeast Geyers Cooperative Tracer Evaluation and Testing Program for the Purpose of Estimating The Efficiency of Injection

Description: The Southeast Geysers Cooperative Tracer Evaluation Program has been a joint project located in the SE part of the Geysers geothermal field, in Lake and Sonoma Counties, California. A new generation of environmentally benign vapor-phase tracers has been used to estimate the varying degrees to which injectate is being recovered following the significant increase of injected volumes within the Southeast Geysers.
Date: February 12, 2001
Creator: Smith, J.L. (Bill)
Partner: UNT Libraries Government Documents Department

A Feasibility Study of H{sub 2}S Abatement by Incineration of Noncondensable Gases in Vented Steam Flow from Davies-State 5206-1 Geothermal Steam Well, Geysers Geothermal Steam Field, Lake County, California

Description: Determine feasibility of using an incineration-type device to accomplish the required reduction in vent steam H{sub 2}S content to meet ICAPCO rules. This approach is to be the only method considered in this feasibility study.
Date: August 25, 2006
Partner: UNT Libraries Government Documents Department

PG and E Geysers Retrofit Project, Units 1-12. Draft Condensed Report

Description: The purpose of this work is to demonstrate whether there is a cost benefit to Pacific Gas and Electric Company in replacing the present iron catalyst/caustic/peroxide system used in the direct contact condenser units versus an alternative approach using surface condensers and the Stretford System.
Date: August 3, 1979
Partner: UNT Libraries Government Documents Department

PGandE Geysers Retrofit Project, Units 1-12: Final Report, Technical Data, Volume I - Sections 1-8

Description: The purpose of this work is to demonstrate whether there is a cost benefit to Pacific Gas and Electric Company in replacing the present iron catalyst/caustic/peroxide system used in the direct contact condenser units with an alternative approach using surface condensers and the Stretford System for hydrogen sulfide abatement.
Date: August 24, 1979
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

Challenges in determining b value in the Northwest Geysers

Description: Past analyses of the Gutenberg-Richter b-value in the Geysers and other geothermal settings have revealed a deviation from the assumed linear relationship in log space between magnitude and the number of earthquakes. In this study of the Northwest Geysers, we found a gently-sloping discontinuity in the b-value curve. This is especially apparent when comparing the least-squares fit (LSQ) of the curve to the fit obtained by the maximum likelihood estimation (MLE), a widely-respected method of analyzing magnitude-frequency relationships. This study will describe the assumptions made when using each of these two methods and will also explore how they can be used in conjunction to investigate the characteristics of the observed b-value curve. To understand whether slope-fit differences in the LSQR and MLE methods is due to physical properties of the system or due to artifacts from errors in sampling, it is extremely important to consider the catalog completeness, magnitude bin size, number of events, and differences in source mechanisms for the events comprising the study volume. This work will hopefully lead to informative interpretations of frequency-magnitude curves for the Northwest Geysers, a geothermal area of ongoing high-volume coldwater injection and steam production. Through this statistical investigation of the catalog contents, we hope to better understand the dominant source mechanisms and the role of injected fluids in the creation of seismic clustering around nearly 60 wells of varying depths and injection volumes.
Date: February 1, 2011
Creator: Saltiel, S.; Boyle, K. & Majer, 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 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

X-ray evidence for capillary pressure driven flow in preserved core from The Geysers

Description: Improved understanding of fluid storage and transport mechanisms relevant to The Geysers reservoir is fundamental to efficient and economic long term production of steam. X-ray computed tomographs of core from research borehole SB-15D made within 72 hours of drilling show characteristic x-ray attenuation profiles that can only be explained by imbibition of drilling fluid at reservoir conditions. The shape of the profile is highly diagnostic. Early time scans, when interpreted taking into account independent measurements of pore size distribution, permeabilities and capillary pressures for the rock matrix sampled by SB-15D, are consistent with strong capillary suctions for the recovered rocks. This indirect indication of imbibition under reservoir conditions, along with detailed analysis of x-ray attenuation in recovered core, suggests that water content was low in much of the preserved core. These measurements are part of a series of laboratory experiments monitored by x-ray methods intended to evaluate movement of various fluids to determine the relative importance capillarity, Darcy flow and vapor phase diffusion.
Date: March 1, 1997
Creator: Bonner, B.P.; Roberts, J.J. & Schneberk, D.J.
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

Induced seismicity associated with enhanced geothermal system

Description: Enhanced Geothermal Systems (EGS) offer the potential to significantly add to the world energy inventory. As with any development of new technology, some aspects of the technology has been accepted by the general public, but some have not yet been accepted and await further clarification before such acceptance is possible. One of the issues associated with EGS is the role of microseismicity during the creation of the underground reservoir and the subsequent extraction of the energy. The primary objectives of this white paper are to present an up-to-date review of the state of knowledge about induced seismicity during the creation and operation of enhanced geothermal systems, and to point out the gaps in knowledge that if addressed will allow an improved understanding of the mechanisms generating the events as well as serve as a basis to develop successful protocols for monitoring and addressing community issues associated with such induced seismicity. The information was collected though literature searches as well as convening three workshops to gather information from a wide audience. Although microseismicity has been associated with the development of production and injection operations in a variety of geothermal regions, there have been no or few adverse physical effects on the operations or on surrounding communities. Still, there is public concern over the possible amount and magnitude of the seismicity associated with current and future EGS operations. It is pointed out that microseismicity has been successfully dealt with in a variety of non-geothermal as well as geothermal environments. Several case histories are also presented to illustrate a variety of technical and public acceptance issues. It is concluded that EGS Induced seismicity need not pose any threat to the development of geothermal resources if community issues are properly handled. In fact, induced seismicity provides benefits because it can be used as a ...
Date: September 26, 2006
Creator: Majer, Ernest; Majer, Ernest L.; Baria, Roy; Stark, Mitch; Oates, Stephen; Bommer, Julian et al.
Partner: UNT Libraries Government Documents Department

Characterization of Fracture Patterns in the Geysers Geothermal Reservoir by Shear-wave Splitting

Description: The authors have analyzed the splitting of shear waves from microearthquakes recorded by a 16-station three-component seismic network at the Northwest Geysers geothermal field, Geysers, California, to determine the preferred orientation of subsurface fractures and cracks. Average polarization crack directions with standard deviation were computed for each station. Also, graphical fracture characterizations in the form of equal-area projections and rose diagrams were created to depict the results. The main crack orientations within the steam field are predominantly in the N10{degree}E to N50{degree}E direction, consistent with expected fracture directions in a pull-apart basin created by sub-parallel right-lateral strike-slip faults related to the San Andreas fault system. Time delays range from 15--60 ms, similar to the time delays from previous studies at geothermal reservoirs. They have detected a significant increase in time delays between 1988 and 1994, which they attribute to widening of the cracks or filling of the cracks with fluid. Increase in production activities during this time also could have influenced this widening.
Date: September 15, 1999
Creator: Erten, D. & Rial, J. A.
Partner: UNT Libraries Government Documents Department

Santa Rosa Geysers Recharge Project: GEO-98-001. Final Report

Description: The Geysers steamfields in northern Sonoma County have produced reliable ''green'' power for many years. An impediment to long-term continued production has been the ability to provide a reliable source of injection water to replace water extracted and lost in the form of steam. The steamfield operators have historcially used cooling towers to recycle a small portion of the steam and have collected water during the winter months using stream extraction. These two sources, however, could not by themselves sustain the steamfield in the long term. The Lake County Reclaimed Water Project (SEGEP) was inititated in 1997 and provides another source of steamfield replenishment water. The Santa Rosa Geysers Recharge Project provides another significant step in replenishing the steamfield. In addition, the Santa Rosa Geysers Recharge Project has been built with capacity to potentially meet virtually all injection water requirements, when combined with these other sources. Figure 2.1 graphically depicts the combination of injection sources.
Date: October 1, 2002
Creator: Brauner, Edwin Jr. & Carlson, Daniel C.
Partner: UNT Libraries Government Documents Department

PG and E Geysers Retrofit Project: Milestone Report No. 1

Description: Rogers Engineering was contracted to determine the technical feasibility and cost/benefit ratios for Pacific Gas and Electric Company to replace the iron-catalyst/peroxide/ caustic systems with surface condensers and Stretford H{sub 2}S abatement systems for Units 1 through 12 at the Geysers. This Milestone No.1 Report is a 6 week progress report and will not have the cost benefit analyses which is planned for in the Final Report. This report will focus only on Units 1 and-3, which are thought of as typical to Units 2 and 4 in our contract. The work performed analyzes the cooling water cycle for both units and determines the turbine operating back pressure as a function of cold water from the existing cooling towers to the new surface condensers. Any power penalty is noted and assessed to the respective turbine-generator with necessary definition for the reason in heat rate deterioration. The direction of Rogers Engineering Co.'s efforts was the conceptual system analysis for Units 1 and 3. But cooling tower performance differences between Units 1 and 2 influenced the similarity of, the cycle thermodynamics and power output at the generator for these two units. We therefore are reporting on Units One and Two. Units Three and Four are identical with some minor location and piping.
Date: June 4, 1979
Partner: UNT Libraries Government Documents Department

PGandE Geysers Retrofit Project, Milestone Report No. 2 (Units 5-12)

Description: Milestone Report No. 1 was delivered on June 1, 1979 and related to the conversion of Units 1-4. Milestone Report No. 2 describes the conversion of Units 5-12 from direct contact condensers which use the iron-catalyst/peroxide/caustic systems to surface condensers and H{sub 2}S abatement with the Stretford Process Unit. This Report is a 10 week progress report that specifically addresses itself to the differences that are encountered between Units 5-6, 7-10 and 11-12. The task schedule shown in the Summary Section was originally presented to PG and E at the Project Kick-Off Meeting on Monday, April 23. Units 11 and 12 retrofit concept which appears in this report was evaluated with a two pass surface condenser running parallel to the turbine shaft. This concept requires the relocation of the turbine lube oil tank, instrument air compressor and battery storage rack facilities. On Wednesday, June 27, the condenser supplier notified Rogers Engineering that it was feasible to design and install a four pass, two tube bundle condenser at right angle condenser to the turbine-generator shaft. The four pass condenser concept will eliminate the need of relocating equipment sensitive to turbine operation. However, schedule requirements for Milestone Report No. 2 left no time to incorporate the benefits of the concept they believe will be recommended by Rogers. It will appear in the Final Milestone Report No. 4.
Date: June 29, 1979
Partner: UNT Libraries Government Documents Department