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Appendix K
Paradox Valley Unit Salt Water Injection Project
The Colorado River Basin Salinity Control Project is located in Montrose County, on the
western border of Colorado. The project diverts naturally occurring seepage of salt brine that
would normally flow into the Delores River (and then into the Colorado River) and injects the
brine underground. The project is operated by the United States Department of Interior, Bureau
of Reclamation. Due to concerns of induced seismicity, seismic data for this project has been
continuously recorded and analyzed since the project began in 1996 in order to understand and
mitigate the effects of any induced seismic events.
The Paradox Valley Unit (PVU) is a group of wells that are part of this project. The brine
is produced from 9 extraction wells before it can flow into the Delores River. The brine is then
injected into one disposal well. The well is located near the town of Bedrock, Colorado,
approximately 1 mile southwest of the extraction wells. The well injects the brine into a
limestone formation at a depth of approximately 14,100 feet to 15,750 feet. The project began in
July 1996 with an initial injection rate of 345 gallons per minute at a pressure of 4,900 psi.
Current injection rates are approximately 230 gallons per minutes at a pressure of 5,300 psi.
The possibility of induced seismicity was addressed during the planning stages of the
PVU injection program because the Paradox Valley Unit injection program was comparable to
both the injection programs at the Rocky Mountain Arsenal northeast of Denver and the water
injection program for improved oil recovery at Rangely, Colorado. Eight years before injection
was begun at the PVU site, the Bureau of Reclamation commissioned a seismic monitoring
network to measure the seismic activity in the Paradox Valley region. The original network
consisted of 10 seismic monitoring stations. The system was upgraded to 16 stations after the
injection began in 1996 and currently totals of 20 stations.
Earthquakes were recorded almost immediately after the beginning of injection in July
1996 with the first seismic event measured in November of 1996. Minor earthquakes continued
through mid-1999 and two magnitude 3.5 events occurred in June and July of 1999. In response
to the higher magnitude earthquakes, the Bureau of Reclamation initiated a program to cease
injection for 20 days every six months. Prior to these events they had noted the rate of seismicity
had decreased during the shutdowns following unscheduled maintenance. The Bureau of
Reclamation hoped stopping injection twice yearly would allow time for the injection fluid to
diffuse from the pressurized fractures into the rock matrix.
After a magnitude 4.3 earthquake occurred in May 2000, PVU stopped injection for 28
days to allow evaluation of the injection program and its relationship to induced seismic events.
After analysis the injection rate was decreased by one third from 345 gallons per minute to 230
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218 APPENDIX K
gallons per minute. The program of ceasing injection for 20 days twice per year was also
continued from June 2000 to January 2002 as were the lower injection rates.
In January 2002 the injection fluid was changed to 100% brine water from a mixture of
70% brine with 30% fresh water, which was the injection mixture from the start of the project.
This heavier fluid increased the hydrostatic pressure measured at the bottom of the injection well
but no difference in the rate of induced seismicity resulted from this change.
After monitoring injection into the Paradox Valley Unit injection well for almost 15
years, the Bureau of Reclamation has recorded over 4,600 induced seismic events. The largest
seismic event occurred on May 27, 2000 and had a magnitude of 4.3 (see Figure K.1). After
reviewing data on injection volume, injection rate, downhole pressure, and percent of days
injecting, the Bureau of Reclamation noted “Of the four injection parameters investigated, the
downhole pressure exhibits the best correlation with the occurrence of near-well seismicity over
time” (Bureau of Reclamation, 2009). The Bureau of Reclamation also noted the record of
seismic activity appears to be divided into three distinct clusters occurring from 1997 to Jan
2000, 2003 to 2005, and July 2008 to present. The Bureau of Reclamation concludes “There
appears to be a gross correlation between the three periods of increased near-well seismic
activity and periods of increased time-averaged injection pressures” (Bureau of Reclamation,
2010). These conclusions reiterate the results of other investigations into the cause of induced
seismicity initiated by underground injection.
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APPENDIX K 219
Figure K.1 Twenty-year dataset collected by the Bureau of Reclamation for the Paradox Valley project.
Upper figure shows the average daily injection flow rate in gallons per minute. Lower figure shows all
induced events and their magnitudes over the same period with distance from the injection well.
SOURCE: Block (2011).
The Bureau of Reclamation continues to inject saline fluids underground as part of the
Colorado River Basin Salinity Control Project and they continue to control induced seismicity by
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220 APPENDIX K
the biennial shutdown of injection activity and by limiting the volume of fluid injected. Both of
these actions minimize downhole injection pressure in an effort to limit induced seismic events.
REFERENCES
Block, L. 2011. “Paradox Valley Deep Disposal Well and Induced Seismicity.” Presentation to
the National Research Council Committee on Induced Seismicity Potential in Energy
Technologies, September 14, Dallas, TX.
Bureau of Reclamation. 2009. Overview of PVU-Induced Seismicity from 1996 to 2009 and
implications for Future Injection Operations. Technical Memorandum No. 86-68330-
2009-22.
Bureau of Reclamation. 2010. 2009 Annual Report Paradox Valley Seismic Network, Paradox
Valley Project, Colorado. Technical Memorandum No. 86-68330-2010-07.
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