Geoscience Reference
In-Depth Information
Paradox Valley Unit
Saltwater 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 U.S. Department of the
Interior, Bureau of Reclamation. Due to concerns of induced seismicity, seismic data for
this project have 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 nine 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 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 20 stations.
Earthquakes were recorded almost immediately after the beginning of injection in July
1996 with the first seismic event measured in November 1996. Minor earthquakes con-
tinued through mid-1999, and two magnitude 3.5 events occurred in June and July 1999.
In response to the higher-magnitude earthquakes, the Bureau of Reclamation initiated a
program to cease injection for 20 days every 6 months. Prior to these events they had noted
the rate of seismicity had decreased during the shutdowns following unscheduled main-
tenance. 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
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