--> Using Sequence Stratigraphy to Optimize Target Selection in Shale Plays of the Rockies (and Beyond)

AAPG Rocky Mountain Section Meeting

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Using Sequence Stratigraphy to Optimize Target Selection in Shale Plays of the Rockies (and Beyond)

Abstract

Sequence stratigraphy is not THE answer in optimizing the selection of horizontal targets in shale plays. But it is an extremely useful, and oftentimes necessary, tool that should be used to assess reservoir intervals and improve geosteering. Sequence stratigraphy can aid subsurface geologic interpretation and evaluation in numerous ways. It (1) provides an increased understanding of depositional controls on reservoir vs. non-reservoir facies, (2) promotes better well-log correlations, (3) aids in reservoir prediction, (4) offers a framework for data integration, (5) guides sample collection from core, (6) delivers better reservoir flow models and volumetric calculations, (7) helps in choosing and staying within the target zone, and (8) furnishes input for completion design. This talk focuses on optimizing horizontal targeting in shale reservoirs based on sequence stratigraphic concepts. Examples from the Marcellus, Eagle Ford, Niobrara, Mowry, and Avalon shales reveal the significance of assessing reservoir quality and mechanical properties within a systems tract and parasequence framework. The best targets typically comprise load-bearing grains and a brittle framework, plus contain large, interconnected pores. When sediment influx is dominantly extrabasinal (detrital), load-bearing grains are delivered during highstands and lowstands. Connected interparticle pores in these systems tracts often yield the best hydrocarbon storage and deliverability. In contrast, the basal condensed section in extrabasinal systems may be the most organic-rich interval, but unconnected organic-matter pores frequently dominate, typically yielding lower flow rates and even creating drilling problems. In contrast, when input is largely intrabasinal (biogenic), late transgressions and condensed sections commonly yield microfossil-rich, brittle deposits. Interconnected interparticle pores and natural as well as induced fracturing usually make these systems tracts the optimum targets.