Passive seismic events (aka "microseismics" or "microearthquakes") are induced during hydrocarbon and geothermal fluid production and reservoir development operations. Microseismicity typically results from shear stress release on pre existing faults and fractures due to production/injection induced perturbations to the effective stress conditions. These stress changes may be due to reservoir depletion, water flooding or stimulation (ie hydraulic frac) operations.

Microseismic frac monitoring

After being a niche technology for many years microseismic monitoring has now emerged as a valuable tool for evaluating the effectiveness of hydraulic fracturing operations. In particular in the USA it is becoming a routine diagnostic technique in hydraulic frac monitoring. Specific examples include development of the;

• tight, unconventional-gas plays such as Barnett Shale and Fayettville Shale, where microseismic monitoring has had a direct impact on both hydraulic fracturing strategy and the reduction in horizontal well spacings
• tight-gas sand plays such as the Bossier sands and Cotton Valley sands in East Texas
• tight-gas sand plays in the Piceance basin and Pinedale-Jonah in the Green River Basin

Illustrations of this growing use include;

Barnett Shale monitoring: Society of Petroleum Engineers ATCE 2005

Bossier sands frac monitoring: World Oil Magazine Bossier sands article

Cotton Valley sands monitoring: SEG Geophysics paper

Cotton Valley sands monitoring: Bulletin Seismological Society America (SSA) paper

Piceance basin monitoring: Society of Petroleum Engineers (SPE) ATCE 2005

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