--> ABSTRACT: Sequence Stratigraphic, Paleobathymetric, and Tectonic Controls on Reservoir Architecture in Lower Permian (Chase Group), Cyclic Carbonates in the Midcontinent USA, by S. J. Mazzullo; #91021 (2010)

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Sequence Stratigraphic, Paleobathymetric, and Tectonic Controls on Reservoir Architecture in Lower Permian (Chase Group), Cyclic Carbonates in the Midcontinent USA

MAZZULLO, S.J.

95 percent of the 80 TCF of gas reserves in midcontinent Permian rocks is from carbonate reservoirs in the Chase Group (Wolfcampian). Outcrop studies provide model-analogs useful in the characterization of these reservoirs. The section includes 7 depositional sequences, each of which is hierarchally divided into 2 higher-frequency cycles. Cyclic sedimentation reflects glacio-eustatic forcing superimposed on continual subsidence over time. The two principal reservoir-analog facies, subtidal carbonate sands and peritidal dolomudstones, contain different but multiple pore types. Spatial occurrence of these facies in any given stratal unit is predictably related to relatively high- frequency cyclicity, paleobathymetry, and at times, syndepositional tectonism.

It was the hierarchy of cyclicity, however, that exerted fundamental control on reservoir architecture. Marine accommodation increases accompanying relatively high-magnitude eustatic fluctuations were sufficient to maintain marine conditions, and resulted in a dominance of porous sands in the basal Chase Group. These sands are of relatively limited areal extent, and some are associated with type-1 unconformities. Lower-magnitude eustatic fluctuations and accommodation increases instead resulted in areally extensive progradation of progressively more dolomitized peritidal facies in the upper Chase Group; peritidal deposits and dolomites are virtually absent in older beds. The up-section change from laterally heterogeneous limestones to more extensive and laterally homogeneous dolomites reflects depositional history as controlled by the character of cyclicity, and predictively explains the contrasting production characteristics of these gas reservoirs in the subsurface.

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