Hydraulic Fracturing in Eola Field, Garvin County, Oklahoma, and Potential Link to Induced Seismicity - Induced Seismicity Potential in Energy Technologies - page 211

Hydraulic Fracturing in
Eola Field, Garvin County,
Oklahoma, and Potential
Link to Induced Seismicity
A hydraulic fracture treatment in January 2011 in Eola field, Oklahoma, coincided with
a series of earthquakes. Eola field is located in central Oklahoma, southwest of Oklahoma
City (Figure J.1). Felt seismicity was reported on the evening of January 18 from one resi-
dent near Elmore City, Oklahoma. Further analysis showed 50 earthquakes occurred that
evening, 43 of which were large enough to be located, ranging in magnitude from M 1.0
to M 2.8. The earthquakes are coincident in location and timing with a hydraulic fracture
in the Eola field, Picket Unit B well 4-18. The events all occurred within 24 hours of the
first activity. The deepest hydraulic fracture in the Picket Unit B well 4-18 occurred 7 hours
before the first earthquake was detected. Most of the events appear to be about 3.5 km
(2.2 miles) from the hydraulic fracture well (Figure J.2).
Accurate event locations were difficult to establish; the closest seismic station was
35 km (22 miles) away from the locus of the events. Errors in location are estimated to be
100-500 m (~100 to more than 500 yards) in ground distance and twice that for depth. The
hypocenter depths are approximately 1 to 5 km in depth, similar to the injection depth for
the 4-18 well (Figure J.3).
Other cases of suspected induced activity in Oklahoma have been reported in the past.
For example, in June 1978, 70 earthquakes occurred in 6.2 hours in Garvin County after
a hydraulic fracture treatment. In May 1979, a well was stimulated over a 4-day period,
where three different formations were hydraulically fractured over at depths of 3.7, 3.4,
and 3.0 km (2.2 to 1.8 miles). The first and deepest hydraulic fracture stage was followed
by 50 earthquakes over the next 4 hours. The second stage was followed immediately by
40 earthquakes in 2 hours; no activity was associated with the third and shallowest hydraulic
fracture (Nicholson and Wesson, 1990). The largest event in the sequence was M 1.9. Just
two of the earthquakes were felt. The activity was 1 km (0.6 miles) away from the Wilson
seismic station in Oklahoma.
South central Oklahoma has experienced historical seismicity (Figure J.4) and has been
the most seismically active part of the state since 1977. A series of Earthscope Transport-
able Array stations were located near the events by coincidence; without these stations, a
majority of the earthquakes could not be located.