Energy Technologies: How They Work and Their Induced Seismicity Potential - Induced Seismicity Potential in Energy Technologies - page 62

Shallowest/youngest
Intermediate depth/age
Deepest/oldest
FIGURE 3.11 Location of areas of active exploration and/or production for shale hydrocarbons (oil
and gas) in the contiguous United States. Light pink areas are major sedimentary basins; dark pink areas
(e.g., Eagle Ford, Barnett) are under active development and production for gas or oil from shale; orange
areas are prospective regions currently being explored for potential oil or gas development from shale.
Several shale units of different ages may overlie one another, and these units are outlined in thick red,
blue, and purple lines representing youngest to oldest shale units, respectively. A "play" is a set of oil or
gas accumulations that share similar geologic, geographic, and time characteristics. SOURCE: EIA (2011).
Available at www.eia.gov/pub/oil_gas/natural_gas/analysis_publications/maps/maps.htm.
occurred in the late 1990s and continues to the present day; estimates suggest that today
approximately 60 percent of the wells drilled are hydraulically fractured (Montgomery
and Smith, 2010).
A typical production well in shale is drilled vertically to an appropriate depth and
then turned horizontally to extend the well bore through the target shale formation. The
horizontal segment (or “lateral”) of the well typically extends over 1-2 miles (~1.8-3 km)
(Box 3.5). To facilitate the flow of the gas or oil into the well bore, the permeability through
the shale reservoir is increased by the creation of artificial fracture networks in the shale
around the horizontal portion of the well bore through the process of hydraulic fracturing
(Box 3.5). Microseisms generally of M < 0 are induced during a hydraulic fracture treat-
ment, and the locations of these microseisms are used to help understand the location of