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Abstract: Characterization of Lower Permian, Cyclic Carbonate Reservoirs (Chase Group) in the Midcontinent Based on Outcrop Model-Analogs


95% of the original 80 TCFG reserves in the midcontinent is from the Chase Group in Hugoton-Guymon fields. Outcrops in Kansas, Nebraska and Oklahoma are model-analogs of the occurrence and complex reservoir architecture in these fields. The rocks compose a glacio-eustatic and tectonically-forced section of 7 depositional sequences and component higher frequency transgressive-regressive cycles deposited on a broad ramp. Principal reservoir-analog facies are distal-ramp, subtidal lime sands and proximal-ramp, peritidal dolomudstones that compose the regressive systems tract within sequences. Multiple pore types characterize these facies, which are laterally and vertically heterogeneous in terms of porosity and permeability distribution. Bryozoan reef facies, present in outcrops, have not been reported as a reservoir facies in the subsurface.

Architecture of porous facies was predictably controlled by the nature of hierarchal cyclicity and history of accommodation. Subtidal sands are the dominant reservoir-analogs in the lower Chase Group because of deposition during a time of relatively high-magnitude eustatic fluctuations that precluded peritidal deposition. Most of these reservoirs are associated with type-1 unconformities and forced regressive systems. In contrast, progradational peritidal facies of more extensive areal extent progressively replaced carbonate sands as reservoir-analog facies in the upper Chase Group. The normal regressive systems within which this facies occurs were deposited during a time of decreasing marine accommodation and lower-magnitude eustatic fluctuations.

AAPG Search and Discovery Article #90944©1997 AAPG Mid-Continent Section Meeting, Oklahoma City, Oklahoma