Measurements of Hydraulic-Fracture-Induced Seismicity in Gas Shales
- Norman Raymond Warpinski (Pinnacle) | Jing Du (Halliburton) | Ulrich Zimmer (Pinnacle Technologies)
- Document ID
- Society of Petroleum Engineers
- SPE Hydraulic Fracturing Technology Conference, 6-8 February, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 5.4.2 Gas Injection Methods, 4.6 Natural Gas, 3 Production and Well Operations, 1.2.3 Rock properties, 5.1.2 Faults and Fracture Characterisation, 1.10 Drilling Equipment, 2.5.2 Fracturing Materials (Fluids, Proppant), 2.5.4 Multistage Fracturing, 5.8.1 Tight Gas, 1.2.2 Geomechanics, 4.1.2 Separation and Treating, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 5.8.2 Shale Gas, 4.1.5 Processing Equipment, 4.3.4 Scale, 5.4.1 Waterflooding, 5.9.2 Geothermal Resources
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Hydraulic fracturing is an essential technology for hydrocarbon extraction from both conventional and unconventional reservoirs. Recently, concern has developed regarding induced seismicity generated in association with multistage fracturing of horizontal wells in shale reservoirs. 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.
Hydraulic fracturing is an important technology for the extraction of hydrocarbons from many reservoirs throughout the world. 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 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 much 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 aquifer. 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.
It is well-understood that long-term injection of fluids in the deep subsurface can induce earthquakes in some circumstances. Nicholson and Wesson (1990) documented numerous cases of minor earthquakes that were likely induced by local injection operations, the most notable of which was the US Army's injection of chemical waste into a 12,000-ft deep interval at the Rocky Mountain Arsenal in Colorado in the 1960s. Similarly, geothermal injections are potential sources of induced seismicity (Fehler 1989; Majer 2005; Smith et al. 2000), often because the optimal geothermal sites are in areas where faults and tectonics are likely to be conducive to earth movement. Other long-term injection operations, such as solution mining, water disposal (Ake et al. 2005), and waterfloods, are potential sources in areas where the geologic conditions are favorable (Segall 1989; Zoback and Harjes 1997).
Simplistically, faults are "locked?? because of frictional forces that are primarily a result of the in situ stresses pressing on the fault plane. When the shear stress becomes great enough to overcome the friction, the fault can slip, resulting in an earthquake. Alternately, fluid injection can increase the pore pressure, which acts to neutralize the normal stress on the fault and cause a decrease in the frictional force, again allowing the fault or some other plane of weakness to slip.
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