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PROCEEDINGS, Thirty-Ninth Workshop on Geothermal Reservoir Engineering
Stanford University, Stanford, California, February 24-26, 2014
SGP-TR-202
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Testing the Application of Low Amplitude Seismic Emission Analysis for Detection of
Microseisms Generated by Geothermal Fluid Flow Through Fractures Underlying the
Western Flank of Newberry Volcano, Oregon
Albert F. Waibel1 and Zachary S. Frone
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awaibel@hevanet.com1, zfrone@smu.edu2
Keywords: Newberry Volcano, seismic
ABSTRACT
Davenport Resources was awarded a DOE grant 109 in 2010 to conduct a combination of traditional and innovative geothermal
exploration tools on Newberry Volcano. An important component of this grant was the testing the application of Low Amplitude
Seismic Emission Analysis (LASEA) for detecting and locating low amplitude noise generated by geothermal fluid flowing
through formation fractures. Davenport Resources engaged Apex HiPoint (now Sigma3) to deploy two arrays of seismometers in
cased shallow wells on the western flank of Newberry Volcano. The first array was deployed in December of 2011. The second
array was deployed in September, 2013, and was coordinated with flowing well NWG 46-16. Final analysis is not available, as
processing of data is still on-going. Results to date, however, show signals from the vicinity of NWG 46-16. Additional analysis of
the large data base should show a correlation or lack of correlation between the signals and the timing of the well discharge.
1. INTRODUCTION
Davenport Resources (Davenport) was awarded a DOE grant 109 to test a combination of traditional and innovative exploration
tools for the identification of blind geothermal targets in a volcanic terrain. The test location was the western flank of Newberry
Volcano in central Oregon (Figure 1). Data from drill holes had identified a large thermal anomaly underlying the west flank. Four
deep exploration test wells had been drilled in the northern portion of the western flank. Three of the four holes intersected rock
with measured temperatures from 288°C to greater than 315°C, though no evidence of fracture interconnectivity (wells CE 86-21
and CE 23-22, drilled by California Energy Company and well NWG 55-29, drilled by Davenport). The fourth well, NWG 46-15,
drilled by Davenport, intersected geothermal fluid-bearing fractures with comparable temperature/depth values as the three other
deep wells. This well was not fully tested due to formation problems near the 5,000 ft. depth, below the casing (Waibel et a., 2012;
Waibel, 2013). However this well flowed on its own without stimulation when opened in September 2013.
Zucca and Evans (1992) identified areas within the Newberry Volcano caldera and under the western flank they inferred to host
two-phase geothermal fluid (Figure 2). The inference of boiling geothermal fluid was based on interpretations of seismic velocity
and attenuation. Davenport's geothermal discovery well, 46-16, complements the conclusions of Zucca and Evans.
A critical question for the Davenport scientific team was: What is the geometry of the hydrothermal fracture system identified by
this one-well-point discovery? Results of the MT survey provided no insight into the resolution of this question, as the location of
this hydrothermal cell intersected by well 46-16 was not identified by the MT data. The efforts by Zucca and Evans lead the team to
consider seismic techniques as a possible solution. As part of the Davenport DOE Grant 109 program the team proposed a trial
adaptation of a passive seismic tool used in the oil and gas industry for the location and geometry imagery of fractures hosting fluid
flow. Apex HiPoint (now Sigma3) worked with the Davenport team to design a test program using their newly patented Low
Amplitude Seismic Emission Analysis (LASEA) program. The low-amplitude seismic emission array had been successfully
deployed by Apex Highpoint/Sigma3 in the oil and gas industry to identify the location and geometry of fluid flow within natural
and induced fractures. This experimental program was designed as a test effort to adapt technology from the oil and gas industry to
hydrothermal exploration. Initial questions regarding transferring this tool to a volcanic geothermal environment were: (1) would
the array be able to pick up deeper signals at reasonable distances from each monitoring hole to be useful, and (2) would surface
microseismic noise drowned out any deeper low amplitude signal sources?
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Figure 1: Location Map showing Newberry Volcano in central Oregon. Also shown are the locations of major volcanoes of
the Cascade Range.
Figure 2: Zucca and Evans inferred two-phase hydrothermal location under the caldera and the west flank of Newberry
Volcano (Figure from Zucca and Evans, 1992).
2. METHODOLOGY
Davenport rotary-drilled the upper 700 ft. of proposed temperature gradient wells and cemented casing in each. The location of
these wells were originally picked and permitted to resolve subsurface temperature anomaly boundary questions, and were adapted
for the seismic monitoring test. One additional well site, to the north of NWG 46-16 was proposed and permitted for seismic
monitoring. Funding for this hole was never provided. The Sigma3 LASEA survey deployed three-component 4.5 Hz digital
geophone sondes within the cases wells. Each observation well contained 11, 12, or 13 3-component digital geophone sondes
spaced at 50 ft. The geophones sondes (Figure 3) were manufactured by GeoSpace of Houston, Texas, and are the digital
instruments used by Sigma3 for passive microseismic work in the oil and gas industry. The survey data were continuously
recorded every 0.5 milliseconds but were broken up into records of 10-second units. Each 10-second unit contains all data from
each of the geophones for that time period.
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The field execution of the LASEA test was divided into two arrays in order to accommodate other activities in the area and to
accommodate equipment availability. The southern array with four monitoring wells is located in the southern portion of the
western flank (Figure 4). This is a "blind test" area with no evidence of subsurface fluid flow. Only one temperature gradient well
had been drilled to depth in the area prior to Davenport's work. Equipment deployment and monitoring in the southern array was
conducted in December of 2011. The northern array with five monitoring wells is located in the northern portion of the western
flank (Figure 4). The northern array is located in the vicinity of the two deep exploration wells drilled by Davenport in 2008 (Figure
4, NWG 46-16 and NWG 55-29). It was anticipated by the Davenport scientific team that the northern array would be a true
controlled test of the LASEA microseismic experiment. NWG 46-16 had intersected geothermal fractures (Waibel et al., 2012) and
had a closed-in well-head pressure of 600 psi. During deployment of the geophones in the northern array NWG 46-16 would be
opened at specific intervals to create controlled-timing fluid flow within formation fractures intersected by the well and fluid flow
up the well and through the venturi created by the formation bridge at 5,000 ft. within the well. The fluid flow into and up the well
bore, and the fluid pressure and velocity changes at the venturi would provide subsurface fluid flow signals from known source
points at known times.
Figure 3: One of the high-grade digital geophones, manufactured by GeoSpace of Houston, Texas, deployed by the Sigma3
field team in the monitoring wells.
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Figure 4: Map of the upper western flank of Newberry Volcano, with seismic monitoring holes and deep exploration holes
identified.
3. RECORDING AND ANALYSIS
Microseismic monitoring within the four wells of the southern array (Figure 4) began on the 23rd of December 2011 and continued
through the 30th of December 2011. The data were processed over the following three months with a grid spacing of 100 m in both
north-south and east-west directions. Concerns regarding the ability of the array to receive signals from more than one or two km
were alleviated by the data set showing cultural industrial noise from sources at least 10 km distance (Figure 5). The data set also
showed that processing was dealing with an extremely large volume of signals rather than too few signals. The dominant
microseismic signals that were identified on a recurring basis, with a duration period of near 27 hours, clustered around a north-
northwest strike (Figure 6).
Figure 5: The four highest-amplitude energy clusters are outlined here with start and end times of 0900 to 1600. Given the
regularity of the start and end times of these periods they are almost certainly man-made cultural noise related to daily
business operating heavy equipment somewhere in the area. (from Apex Highpoint/Sigma3 report to Davenport)
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Figure 6: Southern array shows a dominant trend of episodic micro-seismic signals observed in the processed data. The
four larger dots identify the four monitoring well locations. The smaller dots represent resolved signal sites. The grid
spacing is 100 m. Figure from Apex HiPoint, 2012.
Microseismic monitoring of the wells in the northern array occurred from the 8th to the 15th of September 2013. The geophones
were deployed on the 7th and the morning of the 8th of September. Cyclic flowing of NWG 46-16 occurred on the 8th, 9th and
10th. Monitoring continued until the afternoon of the 15 to watch background signals from the NWG 46-16 area, and to monitor
testing that Alta Rock was conducting for their EGS efforts in well NWG 55-29. NWG 46-16 was expected to flow non-
condensable gas during the test. The team was pleasantly impressed that the well also flowed liquid, dominated by drilling mud that
had been left in the hole (Figure 7).
Table 1, 46-16 flow cycle timing:
Date Time Comments
8 September 2013 1410 opened well, flowing gas phase
1605 well started flowing liquid phase
1835 shut well in
9 September 2013 0845 Opened well, flowing gas phase
1122 mixed liquid and gas flow
1144 liquid phase flow
1700 shut well in
10 September 2013 0936 Opened well, flowing gas phase
1017 Oscillating gas and liquid phase flow
1515 Shut well in.
The initial seismic energy computations were made for a single horizontal plane at an elevation of -1250 m (-4101 ft) relative to
mean sea level. This corresponds to approximately 10,000 ft below the mean surface elevation in the area of interest. The size of
the grid spacing for the northern array data processing is 200m in both north-south and east-west directions (the spacing for the
southern array was 100m). The grid plane was 6 km by 6 km centered near the middle of the 5 observation wells, placing well
NWG 46-16 at the northern boundary of the grid.
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Figure 7: Fluid flowing from well 46-16 through a four-inch bleed line, approximately 45 minutes after the liquid-phase
flow commenced. (8 September 2013).
Figures 8, 9 and 10 have been prepared by Sigma3 for an interim report. Figure 8 shows high amplitude signals identified during an
8 hour slice prior to opening well NWG 46-16 the first time. Figure 9 shows the distribution of low amplitude signals during a 12
hour slice which includes the 4 hour 25 minute flowing of well NWG 46-16. Figure 10 shows the distribution of very low
amplitude signals during a 14 hour slice, 5 days after well NWG 46-16 flowed.
Figure 8: Large amplitude signals detected, with a bandpass filter of 15 to 52 HZ, by the northern array prior to opening
well NWG 46-16. The activity detected are likely related to EGS water injection tests run by Alta Rock. Figure from Sigma3
interim report.
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18© SIGMA3 Integrated Reservoir, LLC. All Rights Reserved.
Lowest Amplitudes: September 09 – General activity increases throughout the area and in particular near observation well nn07 which had previously been a particularly quiet location.
nn07
nn09 nn21nn24
nn19
55-29
46-16
Sept 9: 12 AM
Sept 9: 12 PM
Figure 9: Low amplitude signals detected, with a bandpass filter of 15 to 52 HZ, by the northern array during and
subsequent to flowing of well NWG 46-16. Figure from Sigma3 interim report.
Figure 10: Very low amplitude signals, with a bandpass filter of 15 to 52 HZ, detected by the northern array 5 days after the
last flowing of well NWG 46-16. Figure from Sigma3 interim report.
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Figure 11: Grid nodes for this calculation were within the red boundaries shown with a 100 m grid. Seismic data had a
bandpass filter of 40 to 135 Hz. Please note signal pattern in figure 9 which includes this time frame.
4. CONCLUSIONS
The results of the southern array are inconclusive with regard to fluid flow. A dominant recurring pattern of signals with a north-
northwest strike were recorded. The interpretation of this pattern, however, is open speculation. This strike and location do not
match any observed physical surface trends, and does not show up on the gravity, aeromagnetic or MT surveys. There is no obvious
unique interpretation of this signal pattern that is supported by corroborating evidence. Fluid movement along a permeable plane is
possible. A more favored interpretation is that of a planer structure which is capable of reflecting signals from unknown sources.
This structural interpretation is sympathetic to the strike of a volcanic vent trend which passes through the caldera and extends well
to the NNW on the flank of the volcano. The strike is also similar to the strike of the structural boundary between the La Pine
graben along the western edge of the volcano (Waibel et al., 2012).
The northern array should have been a good controlled source test for evaluation of LASEA as a potential hydrothermal exploration
tool. Key to the test was to have monitoring wells located to provide good geometric coverage around well NWG 46-16. Important
monitoring to the north of the well did not happen. All of the completed monitoring wells are to the south of the well, providing
coverage for only a 120 degree arc, leaving a 240 degree arc around the well uncovered. Seismic signals in the vicinity of well
NWG 55-29, particularly the high amplitude signals, are clearly identified and are likely related to EGS fluid injection efforts
designed to induce formation shearing (Figure 8).
The products of data processing to date do not show unique evidence that the array has been able to identify unambiguous signals
generated by movement of hydrothermal fluid within the well bore or in fractures feeding fluid to the well bore. Figure 11 shows
the signal distribution during the second flow episode of well NWG 46-16, though processing data from only the area immediately
in the vicinity of NWG 46-16. Figure 9, which includes the time frame of figure 11, shows signals in the vicinity of NWG 46-16
indistinguishable from a more regional pattern. The high amplitude results prior to flowing well NWG 46-16 shown in figure 8
identify no signals in the vicinity of well NWG 46-16. Low amplitude signals from 5 days after the well had been flowed (Figure
10) show similar signal patterns covering broad areas, including in the vicinity of well NWG 46-16. Comparative processing of
data from non-well-flowing periods, or of the other two flow events, has yet to be completed, leaving the empirical evaluation of
this test incomplete.
A number of issues cannot be addressed until the complete data processing is available. The preliminary results shown in figures 8,
9 and 10 are not encouraging. The results shown in Figure 11 may be encouraging, though the uniqueness of this pattern to NWG
46-16 flow events has yet to be demonstrated. Additional data processing by Sigma3 will cover a depth range from 5,000 ft. to
15,000 ft. with more constrained timing blocks. For now the scientific team eagerly awaits the final data processing results.
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REFERENCES
Apex HiPoint, 2012, Data processing Results: Davenport Newberry Volcano Project. Unpublished report submitted to Davenport
Newberry.
Sigma3, 2014, An Interim Report for the 2013 Newberry Low-Amplitude Passive Seismic Monitoring Project. Unpublished report
to Alta Rock Energy.
Waibel, A., Frone, Z and Jaffe, T.: Geothermal Exploration at Newberry Volcano, Central Oregon, Geothermal Resources Council
Transactions (2012).
Waibel, A., Beard, L., and Oppliger, G.: The Evolving Role of MT in Geothermal Exploration at Newberry Volcano, Oregon,
Proceedings, 38th Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, CA (2013).
Zucca, J. and Evans,J.: Active High-Resolution Compressional Wave Attenuation Tomography at Newberry Volcano, Central
Cascade Range, Jour. Geophys. Res., vol. 97, no. B7, (1992), 11047-11055.