The oil field of the future will comprise denser installations with temporary and permanent seismic sensors. Already today large arrays consisting of three-component geophones are installed at the surface and at the ocean bottom, and temporary installatio n of boreholes are more and more common. The primary purpose of current installations is to record the seismic data generated by active sources (blasts, airguns, vibrators, etc.) in the framework of time-lapse seismics.
The very same instruments can be used for passive monitoring of ambient and induced seismicity. In contrast to active seismics there is no control on the seismic sources. This makes the interpretation of the seismic signal more demanding, but the seismic signals also contain more informa tion. The spatial distribution, the magnitude, the frequency and the source mechanism of seismic events depend on the structural features and the in-situ stress and pressure conditions. Furthermore, since natural seismic events occur in the subsurface the y can illuminate volumes of interest from a different angle as it would be possible by using active sources at the surface. Another feature is that seismic events - in contrast to many active sources - generally radiate both compressional as well as shear waves. Shear waves have in principle a higher resolution capability than compressional waves, and they can be used as a probing tool to detect anisotropy.
The proposed project contains basic research related to the processing techniques and interpretati on methods for passively recorded seismic data. It covers propagation effects due to reservoir properties as well as source characteristics in relation to in-situ conditions. Passive seismic monitoring can provide vital input for the general reservoir man agement, well planning, production optimization and hazard mitigation.
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