Summary

Shales make up a large proportion of the rocks in most sedimentary basins, and form the seal and source rocks for many hydrocarbon reservoirs. In unconventional shale plays, the shale acts as the source rock, reservoir, and seal. Organic-rich shales represent an enormous energy resource, but production from wells in such plays shows considerable lateral variation. Economic production from such formations requires good reservoir quality (RQ), representing the multiple properties defining reservoir potential, and good completion quality (CQ), representing the multiple properties defining the potential for creating and sustaining large surface area in contact with the reservoir. Reliable predrill methods for determining the spatial variation in RQ and CQ are required to optimally locate wells in these low-permeability reservoirs. The variation of seismic reflection amplitude with angle of incidence (AVA) of seismic waves reflected from an interface between two geological layers may be used to obtain predrill information on RQ and CQ. The information from AVA inversion may be analyzed conveniently using rock physics templates, in which the results of inversion are plotted together with the predictions of rock physics models that take into account variations in RQ and CQ. In this paper, the ability of rock physics templates to distinguish between organic-rich and organic-lean shales is investigated using log data from the Eagle Ford Shale.

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