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Seismic Hazard Associated with Shale-Gas-Fracking? The Bowland Shale Case Study
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 75th EAGE Conference & Exhibition - Workshops, Jun 2013, cp-349-00031
- ISBN: 978-90-73834-49-1
Abstract
The phenomenon of micro-earthquakes occurring in the course of shale gas fracking is well known and has been extensively used for fracture mapping. The aspect of a potential seismic hazard resulting from these earthquakes is fairly new and there exist only few documented cases of fracking induced seismicity strong enough to be perceptible on the Earth’s surface. Recent examples are two felt micro-earthquakes induced by fracking operations in the Bowland Shale (UK). Here we present the results of a geomechanical study explaining the circumstances under which such exceptionally strong earthquakes may occur. From observation data we find evidence that the treatment well in the Bowland Shale intersects a critically stressed (natural) fault or similar plane of weakness. Micro-earthquakes are induced on the existing fracture plane by fluid pressure diffusion and co-seismic stress redistribution. Based on these physical processes we have developed a numerical model of the induced seismicity yielding results which are consistent with observation data. Using the numerical model we estimate the maximum magnitude that could potentially occur by similar hydraulic treatment operations in the Bowland Shale. The resulting magnitude is considered to be too small to cause damage at the Earth’s surface. To account for parameter uncertainties, we have developed an additional traffic light system for controlling future fracking operations.