Micro-earthquake Analysis for Reservoir Properties at the Prati-32 Injection Test, The Geysers, California

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1 PROCEEDINGS, Fourtieth Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, January 26-28, 2015 SGP-TR-204 Micro-earthquake Analysis for Reservoir Properties at the Prati-32 Injection Test, The Geysers, California Lawrence Hutchings 1, Brian Bonner 1, Steve Jarpe 2, and Ankit Singh 1 1 Lawrence Berkeley National Laboratory, Berkeley, California Data Solutions, Inc. Prescott Valley, AZ ljhutchings@lbl.gov ABSTRACT We demonstrate an analysis of micro-earthquake data in a geothermal environment to model reservoirs. The goal is to identify fractures, the state of fluids, and permeable zones. The approach is to extract as much information as possible from micro-earthquake recordings. We obtain earthquake source properties (hypocenters, magnitudes, stress drops, and moment tensors), 3D isotropic velocity (Vp and Vs) and attenuation (Qp and Qs, seismic quality factors), derived elastic moduli (Lambda, Bulk and Young's moduli), and Poisson's ratio. We then utilize rock physics in interpretation to identify reservoir properties. We also test an approach where reservoir properties are determined rapidly, with high resolution, and cheaply. To this end, we have developed an inexpensive, automated micro-earthquake data collection and processing system and computational capability necessary to record and process large numbers of micro-earthquake recordings and obtain tomographic images at lower costs and in a shorter time frame than has been previously possible. Such information provides the basis for reservoir analysis. The easily deployable nature of our system allows for potential large-scale assessment of resources in regions throughout the world. Further, the system s low hardware cost, simple operation, and automated data processing make it attractive to small companies and developing countries with little money and few trained personnel to process and analyze data. We apply the system to the Enhanced Geothermal System (EGS) demonstration project at the northwest part of The Geysers, California (Figure 1). 1. INTRODUCTION Micro-earthquakes with magnitude (M<~3) often occur naturally or due to fluid injection or production in geothermal, CO2 sequestration, hydrocarbon, and natural gas reservoirs. In geological environments where sufficient numbers occur, micro-earthquakes offer a source of energy that can provide information not often achieved by other methods. In this paper we demonstrate an analysis of micro-earthquake data in a geothermal environment. The goal is to identify fractures, state of fluids, and permeable zones. Our approach is to extract as much information as possible from micro-earthquake recordings. We obtain earthquake source properties (hypocenters, magnitudes, stress drops, and moment tensors), 3D isotropic velocity (Vp and Vs) and attenuation (Qp and Qs, seismic quality factors), derived elastic moduli (Lambda, Bulk and Young's moduli), and Poisson's ratio. Further, we examine how rock physics can be used in interpretation of micro-earthquake recordings to identify reservoir properties. Figure 1. The Geysers study area, north of San Francisco, California. 1

2 Figure 2. The study area and instrument locations. "white" symbols are permanent LBNL network stations; "yellow" are temporary DOE monitoring sites; and, "red" are supplementary instruments installed by LBNL for the Prati-32 test. Only instruments located within the study area were used for the tomography, except C08 was also used. We also test an approach where reservoir properties are determined rapidly, with high resolution, and cheaply. To this end, we have developed an inexpensive, automated micro-earthquake data collection and processing system and computational capability necessary to record and process large numbers of micro-earthquake recordings and obtain tomographic images at lower costs and in a shorter time frame than has been previously possible. Such information provides the basis for reservoir analysis. The easily deployable nature of our system allows for potential large-scale assessment of resources in regions throughout the world. Further, the system s low hardware cost, simple operation, and automated data processing make it attractive to small companies and developing countries with little money and few trained personnel to process and analyze data. We apply the system to the Enhanced Geothermal System (EGS) demonstration project at the northwest part of The Geysers, California (Figure 1). We examine a 6 x 6 km lateral and 5 km deep volume. Figure 2 shows this study area and locations of seismic recording stations. The Geysers geothermal field located in the Coastal Ranges, just north of Napa Valley. The region is dominated by the plate boundary motion along the San Andreas Fault. The Geysers is nested between the Southwest-bounding Maacama Fault and the northeastbounding Collayami Fault, and includes a mixture of strike-slip and thrust faults [McLaughlin, 1981]. The subduction of the Farallon plate beneath the North American plate led to Pliocene-Holocene volcanism, which left enough heat to metamorphose the graywacke of the overlying Franciscan mélange to biotite [Moore and Gunderson, 1995]. On October 6, 00:00:01.0 injection into P32 began with an initial rate of gallons per minute for 12 hours that was then reduced to 400 gallons per minute (gpm). The rate was maintained for 54 days until November 30, 2011, when it was raised to 1000 gmp. We analyze data recorded in the study area surrounding the Prati-32 well for a period of one month prior to injection (September 06 through October 05, 2011) and two months after injection (October 06 to December 05, 2011). The basic premise of this paper is that this injection of water provides good knowledge of the spacial and temporal parameters of a created reservoir, which offers the opportunity to validate tomographic inversion techniques and test rock physics theories to identify reservoir properties in a geothermal environment. 2. CRACKS, FRACTURES AND FAULTS We are primarily interested in identifying the state of fluids and permeability from fluid flow through cracks, fractures or faults. The coupling between fluid flow and cracks and fractures depends on the micro-structure of rocks. Cracks are presumed to be associated with weak grain boundaries, fractures are in the scale of multiple cracks, and faults are dislocations from earthquakes. In the most general case, the nucleation and propagation of cracks associated with brittle deformation may increase the connectivity between cracks and fractures, and thus permeability. Faults are considered tectonic in nature and aligned with regional stress patterns. Microearthquakes themselves occur on new or preexisting fractures or faults, and in general, create permeability. Therefore, accurate location of micro-earthquakes can identify possible permeable zones, and their moment tensors can identify the orientation and type of fractures being formed. In some environments permeability is contained in large cracks, as in the Salton Sea (Daley, 1984). O Connell and Budiansky (1974) relates the crack density parameter to the effective Poisson s ratio. 2

3 We assume micro-earthquakes associated with fractures to rupture the entire length of a preexisting alignment of cracks or fractures, and micro-earthquakes on faults to rupture only part of a larger feature created by previous earthquakes. The rupture process and resulting permeability from micro-earthquakes may not be identical at all scales. Micro-earthquakes that rupture the entire crack or fracture may have an end effect, i.e. there has to be deformation at the end of the fracture to accommodate the slip (Johnson, 2014). Following Simpson et al. (2001) frictional sliding along preexisting cracks gives rise to tensile wings to accommodate dislocations at the end of fractures. Johnson (2013) interpreted moment tensor solutions to indicate the existence of wing fractures at The Geysers. Guilhem et al (2013) intrepreted a combination of istropic movemt at the beginning of fractue (from first motion soltutios) to be followed by deviatoric slip (from full moment tensr soutions). Rocks that contain aligned single cracks system will cause anisotropic wave propagation. If cracks are aligned in parallel shear-wave splitting will occur. In geothermal environments, high heat flow may cause shear-wave velocity anisotropy to be higher than normal and to potentially reach values as high as 10 per cent (Crampin & Booth 1989, Elkibbi, 2005). 3. ROCK PHYSICS Rock physics applied to the interpretation of micro-earthquake recordings describes the effects of fluids, fractures, mineralogy, porosity, pore pressures, and permeability on seismic velocity, attenuation, and elastic parameters. Rock physics has been used in interpretation of recordings of active seismic sources, primarily for oil and gas studies (Berryman, 2007; Mavko,et al, 1998). Few studies have made an attempt to obtain a fundamental understanding of the relationship between micro-earthquake recordings and material and fluid properties. Several authors have previously interpreted micro-earthquake studies with rock physics (Julian et al., 1996; Foulger et al., 1997; Berryman et al., 2002; Foulger et al., 2003; Hatchell and Bourne, 2005; Grechka et al., 2010). 3.1 Vp, Vs, Qp, Qs and Their Gradients with Depth Q is the seismic coefficient and has reciprocal effect as attenuation; i.e. high Q is low attenuation. Attenuation is both extrinsic whereby energy is lost due to scattering along small fractures or at interfaces; and intrinsic, whereby energy is lost due to fluid moving between pores as the fluid pressure attempts to equilibrate by diffusion (Berryman, 1977). In the presence of fractures both Vp and Vs will decrease due to a decrease in rigidity, and both Qp and Qs will decrease due to an increase in extrinsic attenuation. In addition to small cracks, faulting and fracturing increases extrinsic attenuation. Therefore, an indication of faulting or fractures at depth is the drop in Q relative to surrounding rock. Partial saturation increases intrinsic attenuation due to fluids moving between pores. Intrinsic attenuation generally ceases at full saturation. Although there can be some movement between pores. These effects are different for different geology, and can vary significantly with different conditions within the same geology. Vp, Vs, Qp and Qs generally increase monotonically with increasing depth due to the close of fractures from the lithostatic load. Therefore, a fractured geologic material is predicted to have low velocities and Q near the surface, with velocities and Q increasing with depth, where fewer thin cracks remain open as pressure increases (Tarif et al., 1988; Boitnott and Bonner,1994). Once crack are closed, velocity and Q will no longer increase rapidly with depth. Intrinsic attenuation is unaffected by lithostatic load, unless pores are also closed. Work in the laboratory suggests that using attenuation and velocity in combination can improve discrimination of pore fluid content. Winkler and Nur (1979) measured moduli and attenuations for longitudinal and trosional modes in porous and cracked rock near one khz where intrinsic attenuation dominates scattering. Plotting the data in Qp/Qs, Vp/Vs coordinates separates dry, partially saturated and fully saturated conditions. These data can not be used quantitatively until more measurements are done, using currently available methods for low frequency measurements (Hofman et al., 1999; Nakagawa, 2011, and references). However, the strong trends in the Winkler data suggest that field data should reflect similar effects. Further, geochemical reactions at grain scale can cement fractures and stiffen the rock, and diminish the effect of grain scale fractures on the velocity. This is observed in laboratory measurements of velocities for recovered core from The Geysers (Boitnott and Bonner, 1994). This suggests that much of the observed velocity depth dependence in Vp and Vs in the Geysers reservoir rocks is likely due to closure of larger scale fractures. Ito et al., (1979) showed that that as steam dominated porous rock converts to fluid, due lower pressure or temperatures, Vs will decrease due to increain density, but Vp will increase due to an increae in bulk moduli. Interpretations of these observations include: (1) decreased velocities and decreased Q are an indication of dry fractures at depths due to decrease in rigidity and an increase in extrinsic attenuation; (2) increased veleocity and Q, as conmparred to surrouonding rock, is an indication of dry unfractured rock; (3) decreased Vs and increased Vp along with an increase in Q, relative to surrounding rock, is an indicationi of fully sturated fractured rock; this is due to the decrease in intrinsic Q and reduction of shear modui and increase in bulk modulus; (4) increased Vp and slightly decrease Vs and increased Q is an indication of fully saturated relatively unfractured material when comparred to surroundign rock; this is due to increased bulk moduli, increase in density and increase in intrinsic Q; (5) increased velocity and increased attenuation with depth is an indication of either fully saturated or fully gas-filled pores; where the defining difference would then be the difference between velocities with surrounding rock, where fully saturated material has a lower Vp/Vs ratio. These relationship and others are used intrepret tomographjic inversin resutls for reservoir properities. 3.2 Temperature and Pressure Rocks subjected to high temperatures and pressures undergo a transition from brittle to crystalline plastic behavior. The temperature of this transition ranges from around 300 C, for quartz to around C for feldspar; the transition temperature also depends on pressure and strain rate (Scholtz, 1990). As temperature increases, the shear modulus decreases, affecting both Vp an d Vs. As it approaches liquid the shear modulus approaches zero and no shear wave propagate. 3

4 The effect of temperature can occur in opposition to the pressure effect (Tarif et al., 1988). At The Geysers, Prati-32 well temperatures have been measured to near 350 o C, so these effects could be significant. In a dynamic situation heating or cooling of fluids within pores can cause fractures. Experiments where granite was cooled from different high temperatures up to 646 o C showed permeability increased up to a 1000 times over original values (Darot et al., 1992). Darot et al. also found permeability decreased rapidly with confining pressure, being effectively zero for confining pressures over 30 MPa. 3.3 Permeability and Saturation The effect of fluids on observations of seismic wave propagation can be significant. Fluids cannot support shear stress, and therefore don't affect the shear modulus at low frequency, but the inclusion of fluids increases the density and stiffness of pores to compression (bulk modulus, Gassmann,1951). Therefore, the effect of saturation on Vp is the result of competing effects of lowering it due to increased density, but increasing it due to increased resistance to compression (increase bulk modulus). Vs should decrease only do to increased density because rigidity is not affect by the incompressible fluids. Both Qp and Qs should increase due to full saturation due to decrease of fluid flow between pores (intrinsic attenuation). Monitoring the migration in time and space of the micros-seismic cloud associated with fluid injection can be used to estimate permeability from diffusivity (Grechk Vs as the density increases with saturation, in the absence of chemical interactions. However, there is a compensating effect between λ and density, so that there is less of a change in Vp. Therefore, relative to surrounding rock, for example, Vs will decrease more than Vp with saturation under these conditions. Thus, another indication of the reservoirs is a diminished value Poisson's ratio, by the same argument. In general, permeable zones cannot be differentiated from saturated non-permeable zones by observations of micro-earthquake recording alone. However, saturation can be identified. There are five primary interpretations of permeability and saturation from observable micro-seismic data: (1) permeability may be inferred from high attenuation (low Qp and Qs) in fluid bearing rock if the loss mechanism is intrinsic as discussed above. Lower Qp and Qs due to extrinsic attenuation and lower Vp and Vs due to decreased rigidity can identify high fracture density, which in turn implies high permeability if the fractures intersect and are sufficiently open (Kachanov and Grechka, 2006,TLE); and (3) monitoring the migration in time and space of the microsseismic cloud associated with fluid injection can be used to estimate permeability from diffusivity (Grechka, et al., 2011); (4) Regions of high velocity gradients in field data may well be associated with high density of compliant, and thus permeable, fractures. This may be particularly true in geothermal areas where healed micro-fractures will contribute less to observed gradients (Boitnott and Bonner, 1994 and Boitnott, 1995); (5) the nucleation and propagation of cracks associated with brittle deformation may increase the permeability by increasing the connectivity between cracks. Therefore, focal mechanism of micro-earthquakes can identify whether newly created cracks are aligned or randomly oriented and help in identifying permeable zones. 4. INSTRUMENTATION AND DATA PROCESSING The automated micro-earthquake data collection and processing system includes: (1) an inexpensive micro-earthquake recorder that requires very little time and no technician input to install, (2) an automated data processing program to manage data, one that requires merely placing flash memory chips (or telemetry) into a computer, (3) automated creation of meta-data that provides preliminary earthquake locations, moments, magnitudes, and input files for tomography and earthquake source studies, (4) an interactive program for testing micro-earthquake network designs for accuracy and resolution, and (5) and easy to use graphical user interface for a trained professional to examine and update seismogram P- and S-wave picks (Hutchings et al., 2011a). The automation and inexpensive cost for field deployment and maintenance and instrument costs allows for a large number of stations to be used in the analysis, and thus high resolution results can be obtained in shorter amount of time. Also, the increased number of recorders can offset need for borehole instrumentation that can provide an increase in signal to noise ratio (SNR). Figure 3 shows a comparison of the instrument response of the Oyo-11D to a Guralp broadband sensor. 5. TOMOGRAPHY We perform tomography to obtain Vp, Vs, Qp and Qs. We modified SimulPS (Thurber, 1984) to perform double difference tomography for earthquake location and velocity structure and for inversion of pulse widths to obtain a three-dimensional Q models (Hutchings et al., 2014). The inversion for Q is linear and is performed after earthquakes have been located and the velocity model is calculated. We separated data into three time periods: one month prior, one month after, and second month after injection began. 5.1 Velocity Model Results The velocity inversion is simultaneous with locating earthquakes. We allowed events within two kilometers of the exterior nodes to be considered for the first iteration. This allowed events to move into our study area. This included 879, 833, and 985 events with magnitudes M= 0.8, 0.8 and 1.0, respectively; the latter magnitude was used to keep the number of earthquakes and ray paths to be close to the other two time periods. After the initial iteration, we then limited events to be within one node spacing of the study area. Only a few events are outside the tomography volume, and only a small part of the ray paths, at a deep portion of of the volume, are within the constrained extreme nodes. So, the error from events outside the study volume is minimal and worth the increased resolution at the edges of the study area. The final tomography was performed with 303, 394 and 409 earthquakes, respectively, for the three time periods. We achieved a root-mean-square residual of travel times of , and , respectively; and a reduction from the starting model over 80% for each run, albeit with fewer earthquakes. Figures 4 and 5 show a cross section of the final P- and S-wave velocity models near the well bottom for the three time periods. It is apparent that velocity anomalies appear at the bottom of the well after one and two months of injection. The anomaly increase n size for 4

5 the second month. The proximity of the anomalies to the well, the fact that the earthquakes just after injection occur around the well bottom both indicate that the inversion is provides reasonably accurate results. Figure 3. Comparison of recordings with a Guralp sensor and a Reftek recorder response removed (red) to recordings with the Oyo-11D sensor and Jarpe Data Solution's recorder response removed (black). Note, the figure on the right focuses on the the details of the shapes of seismic arrivals. Figure 4. Cross-section of P-wave velocity results for one month before (a), one month after (b), and the second month after Figure 5. Cross-section of S-wave velocity results for one month before (a), one month after (b), and the second month after 5

6 5.2 Rock Physics Interpretation In rock physics interpretation, we look for changes in structure as compared to surrounding rock. Figure 6 shows a cross section through wells Prati-32 and nearby Prati-9 of four parameters before injection. There is no apparent alteration near Prati-32. Also, notice that no earthquakes were located near the bottom of the well. Figure 6. Cross-section of for one month before (a) top left, Vp, (b) top right, Poisson's ratio, (c) bottom left, Qs, and (d) Lambda. Injection has been occurring at Prati-9 for years and it is apparent that the structure at some depth below this well has been altered. Vp and Qs have decreased significantly, Poisson's ratio decreased slightly, and Lambda is unchanged. We interpret these and other parameters not shown to indicate that the fluid injected for Prati-9 has moved down below the well and turned to steam. The drop in Vp and Vs (not shown) is due to fractures where fluids would have increased Vp, but not change Vs. This also results in little change in Poisson's ratio. The lower Qs is another indication of fractures. Another indication of lack of fluid is that Lambda is unchanged. Figure 7 shows changes in parameters after one month of injection. Notice that changes in structure from injection at Prati-32 occur right at the bottom of the well. This confirms the accuracy of the tomography and that the effects of injection at Prati-9 well below the well are accurate. Bulk modulus, Poisson's ratio, and Lambda increased. Vs decreased. Qp and Vp increased slightly and Qs did not change (not shown). We interpret this observation to indicate that there is fluid saturation along with fracturing around the well bottom. Fracturing would decrease Vs, while saturation would not affect Vs. Whereas, saturation would increase Vp, even with fracturing. Saturation and fracturing should have competing effect of intrinsic and extrinsic Q. Saturation should increase intrinsic Qp, but not affect extrinsic Qp. We can't explain the unchanged Qs, unless the effect of increasing intrinsic Qs is offset by a decrease in extrinsic Qs. Poisson's ratio, and Lambda increased, which is another indication of saturation. 6

7 Figure 7. Changes in (a) top left, Bulk modulus; (b) top right, Vs, (c) bottom left, Poisson's ratio, and (d) Lambda after one month of injection. Figure 8 shows changes in parameters after two months of injection, as compared to one month before injection. Bulk modulus and Vp have returned to values comparable to before injection for the volume around the well bottom. A new anomaly in Vp has moved below the well. Vs continues to be low and Lambda and Poisson's ratio continue to be high compared to before injection. These changes have not moved, but increased in size. Qs shows no change for either one or two months after. We interpret these observations to indicate continued saturation, but with increased fracturing. Only Vp and bulk modulus have changed significantly and this is due to the increased fracturing offsetting the saturation. Figure 8. Changes in (a) top left, Vp, (b) top right, Vs, (c) bottom left, Lambda, and (d) Bulk modulus after two months of injection. 7

8 6. CONCLUSIONS High resolution tomography is key to imaging reservoir properties. We have outlined how rock physics can be used in interpretation of micro-earthquake recordings to identify reservoir properties. This is primarily based upon 3D-velocity (Vp and Vs) and attenuation structure (Qp and Qs). Interpretation is still work in progress. We will also utilize earthquake locations, moments, magnitudes, focal mechanism solutions, and laboratory studies for future analysis. We conclude that rock physics offers a means to increase to usefulness of micro-earthquake recordings for interpretation of reservoir properties. ACKNOWLEDGEMENT This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Geothermal Technologies, of the U.S. Department of Energy under Contract No. DE-EE REFERENCES Berryman, J. G. (1995) Mixture theories for rock properties, in Rock Physics & Phase Relations, a handbook of Physical Constants, AGU Reference Shelf 3, Thomas J. Ahrens, Editor, American Geophysical Union, Washington, DC, pp Berryman, James G., Seismic waves in rocks with fluids and fractures. Geophys. J. Int. 171, Berryman, J.G., P.A. Berge, and B.P. Bonner, Estimating Rock Porosity and Fluid Saturation Using Only Seismic Velocities. Geophysics, v. 67, No. 2, p Berge, Patricia, Lawrence Hutchings, Jeffrey Wagoner, and Paul Kasameyer (2001) Rock Physics Interpretation of P-wave Q and Velocity Structure, Geology, Fluids and Fractures at the Southeast Portion of The Geysers Geothermal Reservoir. Geothermal Res. Council, Transactions, 14, 2001 Annual Meeting, San Diego, CA. Bonner, Brian and Lawrence Hutchings, Rock Physics Interpretations for Reservoir Properties from Micro-earthquake Recordings. Geothermal Resources Council Transactions, 34, Bonner, Brian, Lawrence Hutchings, and Paul Kasameyer (2006) A Strategy for Interpretation of Microearthquake Tomography Results in the Salton Sea Geothermal Field Based upon Rock Physics Interpretation of State 2-14 Borehole Logs. Geothermal Res. Council, Transactions, 14, 2007 Annual Meeting, Reno, NV. LLNL, UCRL-PROC Boitnott, G. N. and B. P. Bonner, Characterization of rock for constraining reservoir scale tomography at the Geysers geothermal field, in press, Proceedings of the Stanford Workshop on Geothermal Reservoir Engineering. Boitnott, G. N. (1995) Laboratory Measurements on Reservoir Rocks from The Geysers Geothermal Field. proceedings, Twentieth Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, California, January 24-26, SGP-TR-150. Daley, T.M., T.V. McEvilly, and E.L. Majer, Analysis of P and S Wave Vertical Seismic Profile Data from the Salton Sea Scientific Drilling Project. J. Geophys. Res. v. 93, No. B11, p. 13,025 13,036. Darot, M., Gueguen, Y. and Baratin, M. (1992) Permeability of thermally cracked granite, Geophys. Res. Lett. 19, Elders, W.A., and J.H. Sass, The Salton Sea Scientific Drilling Project. J. Geophys. Res. v. 93, No. B11, p. 12,953 12,968. Foulger, G.R., Grant, C.C., Ross, A. and Julian, B.R. (1997) Industrially induced changes in Earth structure at The Geysers geothermal area, California. GRL, 24(2): Foulger, G. R., B. R. Julian, A. M. Pitt, D. P. Hill, P. Malin, and E. Shalev (2003) "Tomographic crustal structure of Long Valley caldera, California, and evidence for the migration of CO2 between 1989 and 1997", J. geophys. Res., 108(B3), /2000JB Gassmann, F. (1951) (translated, Berryman, Origin of Gassmann s Equationis. Geophysics , Grechka, Vladimir, Prajnajyoti Mazumdar, and Serge A. Shapiro, Predicting permeability and gas production of hydraulically fractured tight sands from microseismic data. GEOPHYSICS, VOL. 75, NO. 1; P. B1 B10. Gunderson (1989) The orientation of steam-bearing fractures at The Geysers Geothermal Field, Geothermal Res. Council, Transactions, 13, Hatchell. Paul and Stephen Bourne (2005) Strain-induced time-lapse time shifts are observed for depleting reservoirs. The Leading Edge; December 2005; v. 24; no. 12; p Ho-Liu, P., H. Kanamori, and R.W. Clayton (1988) Applications of attenuation tomography to Imperial valley and loso-indian well region, southern California. J. Geophys. Res. 93, Hutchings, Lawrence, Steve Jarpe, Katie Boyle, Gisela Viegas, and Ernest Majer (2011) Inexpensive, Automated Micro-Earthquake Data Collection and Processing System for Rapid, High-Resolution Reservoir Analysis. Geothermal Res. Council, Transactions, 2011 Annual Meeting, San Diego, CA. Hutchings, Lawrence, Katie Boyle, and Steve Jarpe (2010) Toward High Resolution Tomography and Rock Physics Interpretation for Reservoir Properties. Geothermal Res. Council, Transactions, 17, 2010 Annual Meeting, Sacramento, CA 8

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