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The AAPG/Datapages Combined Publications Database

Rocky Mountain Association of Geologists

Abstract


The Paradox Basin Revisited – New Developments in Petroleum Systems and Basin Analysis, 2009
Pages 436-470

Regional Lithofacies Trends in the Upper Ismay and Lower Desert Creek Zones in the Blanding Sub-Basin of the Paradox Basin, Utah

Thomas C. Chidsey, Jr., David E. Eby

Abstract

The Middle Pennsylvanian (Desmoinesian) Paradox Formation has produced over 28 million bbls (4.5 million m3) of oil and 70 BCF (2 BCM) of gas in the Blanding sub-basin of the Paradox Basin, Utah. The two main producing zones of the Paradox Formation are the Upper Ismay and Lower Desert Creek. Establishment of the basic carbonate lithofacies belts and stratigraphic patterns within the Ismay and Desert Creek zones in the Blanding sub-basin are critical to exploration efforts and to understanding the reservoir heterogeneity within existing fields. The Ismay zone is dominantly limestone composed of equant buildups of phylloid-algal material. The Desert Creek zone is dominantly dolomite comprising regional shallow-water trends with highly aligned, linear lithofacies tracts that may parallel shorelines. The controlling factors of the depositional environments were water depth, salinity, prevailing wave energy, and, in the case of phylloid-algal growth, paleostructural position.

Examination of Upper Ismay cores identified seven depositional lithofacies: open marine, middle shelf, inner shelf/tidal flat, bryozoan mounds, phylloid-algal mounds, quartz sand dunes, and anhydritic salinas. Lower Desert Creek lithofacies include open marine, middle shelf, proto-mounds/collapse breccia, and phylloid-algal mounds.

Subdividing the Upper Ismay zone lithofacies into Upper and Lower parts delineates two very prospective reservoir trends that contain porous, productive buildups. The mapped lithofacies trends clearly define anhydrite-filled intra-shelf basins. Projections of the inner shelf/tidal flat and mound trends around the intra-shelf basins identify potential exploration targets. Mapping of the Lower Desert Creek zone shows that intra-shelf basins are not present. However, productive mound lithofacies along linear shoreline trends could also serve as a guide to previously undrilled, porous Desert Creek intervals and buildups.


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