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Abstract

In this study, we report results from a surface microseismic monitoring of a 21-stage hydraulic fracturing of a shale gas reservoir along a horizontal well. The depths of hydraulic fracturing range from 2500m to 3020m. A surface array consisting of 45 sensors was deployed around the well, with 27 L22E short-period and 18 CMG-6TD broadband seismometers. For analyzing the continuously recorded microseismic data, we adopted the following steps: (1) event detection, (2) event location, (3) event focal mechanism determination, and (4) microseismic imaging. The double-difference seismic tomography method of Zhang and Thurber [2003] is applied to determine the Vp and Vs anomalies due to the fracturing process. In total, more than 700 events were detected. The events can be categorized into two groups: group I near the wellbore and group II about 500 meters to the east of the wellbore. The group II events are likely induced by the pore pressure increase directly caused by fluid migrated from the fracturing spot or the pressure perturbation caused by undrained response of fluid injection. The velocity tomography shows that the fracturing process causes lower Vp and Vs anomalies around the fracturing zone.

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/content/papers/10.3997/2214-4609.20140575
2014-06-16
2024-03-28
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