--> ABSTRACT: Sequence Stratigraphy: Reservoir Compartmentalization by Facies, Unconformities, Diagenesis and Faulting, by R. J. Weimer; #91021 (2010)
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Sequence Stratigraphy: Reservoir Compartmentalization by Facies, Previous HitUnconformitiesNext Hit, Diagenesis and Faulting

WEIMER, ROBERT J.

The petroleum occurrences in the greater Wattenberg field area, central Denver basin, have been generally interpreted as a basin-center continuous accumulation with no fresh water legs. The Muddy (J) Sandstone, of the Lower Cretaceous Dakota Group, is the most important petroleum-producing formation. In the deeper part of the basin, it is regarded as a tight gas reservoir. The formation is a fine- to medium-grained quartzose sandstone with interbedded siltstone and shale with a thickness from 50 to 150 ft. Re- evaluation of fields and pools from a 3000-well data base clearly shows extensive reservoir compartmentalization.

The reservoirs within the Muddy (J) have unique geographic distributions related to environments of deposition (fluvial, deltaic and marine), Previous HitunconformitiesTop and faulting. Seals in traps for individual pools are related to facies changes to shale, clay plugs in meander belt complexes and diagenesis along faults.

Sequence stratigraphic concepts have provided a new basis for analyzing the petroleum occurrences. By tracing two types of erosional surfaces caused by relative sea level changes, the Muddy (J) Sandstone was subdivided into the J1, J2 and J3 members. Sandstone trends for each member, associated pools and production data, and structure were then mapped by integrating geology, geophysics and petroleum engineering data bases. Thickness of density log porosity greater than 8 percent was mapped for both the J1 and J2 sandstones to delineate economically productive areas.

Evidence for compartments are gas opposite oil at the same structural elevations, gas downdip from oil, and abrupt linear changes in gas-oil ratios.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.