Summary
Hydraulic fracturing is an essential technology for hydrocarbon extraction
from both conventional and unconventional reservoirs around the world.
Recently, concern has developed regarding induced seismicity generated in
association with multistage fracturing of horizontal wells in shale reservoirs.
Microseismic monitoring of hydraulic fractures, which has been a routine
service for over a decade, can provide information about the levels of seismic
activity commonly found during fracturing. A review of thousands of fracture
treatments that have been microseismically monitored shows that the induced
seismicity associated with hydraulic fracturing is very small and not a problem
under any normal circumstances. Results are presented for six major shale
basins in North America in which hundreds to thousands of fracture treatments
have been conducted in predominatly gas reservoirs. This paper reviews the
methodology, the data, and the interpretation of the microseismicity.
In unconventional reservoirs, such as the ultralow-permeability shales that
are now being regularly exploited, it is absolutely essential to hydraulically
fracture a well to obtain economic levels of production (Sutton et al.
2010).
Contrary to media and general public perception, hydraulic fracturing is not
a "new" technology, having been applied since the late 1940s (Montgomery and
Smith 2010). There is also a perception that hydraulic fractures are much
larger than ever, but the "massive hydraulic fractures" that were performed in
the 1970s (Fast et al. 1977; Gidley et al. 1979; Strubhar et al. 1980) were of
similar size to many of the fracture treatments that are conducted in
horizontal wells today. In addition, these large treatments were performed in
shales in the eastern United States (Jennings et al. 1977), with some of the
work supported by the United States government (Overby 1978; Duda et al. 2002)
to prove up the resources in the Devonian shales of Appalachia and the western
tight-gas sandstones of the Rocky Mountains.
A previous paper (Fisher and Warpinski 2011) presented data from
microseismic monitoring that showed fractures are not a threat to propagate
into aquifers. Results from thousands of monitored fractured treatments
demonstrate that fractures will not propagate thousands of feet vertically and
intersect potable water sources. In all of the shale basins studied, fractures
remain several thousand feet below the deepest water source. Hydraulic
fracturing is a safe technology as applied in these shale basins.
Recently, however, there has been considerable attention focused on
earthquakes associated with hydraulic fracturing. Here, as well, microseismic
monitoring is a valuable technology for assessing the earthquake potential of
fracturing operations. The objective of this paper is to present the very large
suite of microseismic measurements available to the authors in the major shale
basins of North America that show that earthquakes are not a threat in any
normal situation involving hydraulic fracturing. Most of the results provided
here are for reservoirs that are predominantly gas, but there are also some
data for reservoirs with greater liquid content; no attempt was made to
separate the two.
© 2012. Society of Petroleum Engineers
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History
- Original manuscript received:
4 November 2011
- Meeting paper published:
7 February 2012
- Manuscript approved:
20 March 2012
- Published online:
25 July 2012
- Version of record:
7 August 2012
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