Summary

4D seismic reservoir monitoring can be defined as “time-lapse 3D seismic surveys acquired and analyzed repeatedly at the same site, multiple times during the life of a producing reservoir, to image dynamic changes in reservoir properties related to fluid flow.”

However, 4D seismic is not simply a trivial extension of 3D seismic. There are significant differences in cost/benefit analysis, signal-to-noise issues, interpretability, and information content. Furthermore, while interpretation of 3D seismic data is essentially a static geology characterization issue, the interpretation of 4D seismic is essentially a dynamic fluid-flow monitoring issue. Therefore, whereas 3D seismic provides a strong link between geology and geophysics to help build a reservoir model suitable for predicting fluid flow, 4D seismic shifts the emphasis to geophysics and engineering to directly map, not predict, fluid-flow data in the inter-well space. This can lead to the false impression that the role of geology may be greatly diminished in 4D seismic monitoring, compared to 3D seismic characterization. in the extreme, a misleading perspective may be that, since the geology is not time-varying between seismic surveys, the geology will subtract out altogether in 4D seismic difference data. This poses a real challenge to geologists to step forward and define the role of geology in 4D seismic studies. Our presentation will address various aspects of this challenge.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah