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HENTZ, TUCKER F., Bureau of Economic Geology, The University of Texas at Austin, Austin, TX

ABSTRACT: Reservoir Framework and Exploration Potential of the Cleveland Formation (Western Anadarko Basin) Using a Sequence-Stratigraphic Model

The Upper Pennsylvanian (lower Missourian) Cleveland Formation has yielded more than 435 bcf of natural gas and more than 18.2 MM bbl of oil from a seven-county tight-gas area in the northeastern Texas panhandle. Regional study of the Cleveland and underlying Desmoinesian Marmaton Group siliciclastics established the sequence-stratigraphic framework to clarify the vertical and areal occurrence of Cleveland reservoirs, seals, and source rocks.

Regionally distinctive facies stacking patterns in the study interval compose a sequence-stratigraphic framework of several westerly sourced systems tracts and three depositional sequences. Sequence 1 (S1) is characterized by landward- and seaward-stepping deltaic/strand-plain cycles (parasequences), deposited on the top-of-Oswego type 1 sequence boundary, that define (in ascending order) Marmaton late-stage lowstand-wedge and transgressive systems tracts (TST) and a lower Cleveland highstand systems tract (HST). A regionally correlative, organic-rich marine-condensed section at the top of the Marmaton TST, equivalent to the Nuyaka Creek black shale bed of mid-continent cyclothems, represents maximum flood conditions during eustatic rise. A relative sea level drop with the onset of S2 deposition initiated development of a sand-rich incised-valley system (LST:iv) in the middle Cleveland that extended basinward of the lower Cleveland shelf break. Subsequent coastal onlap by thin deltaic systems of the overlying TST marks the start of decreased sediment influx during late Cleveland deposition, resulting in thinning of parasequences and an increase in carbonate beds in upper S2 and S3.

Stratigraphic traps and pinch out of reservoir facies within small, southeast-plunging anticlines compose most traps in the producing area. Proximal delta-front and fluvial sandstones of the Cleveland upper HST and overlying LST:iv, respectively, are the primary reservoirs. The high-TOC, top-of-Marmaton marine-condensed section and thick prodeltaic and lower distal delta-front shales within the lower Cleveland HST are the probable source rocks. Distal deltaic shales of the middle Cleveland TST form most reservoir seals. Potential new reservoirs should be targeted at the updip terminations of systems tracts, at lapout positions of individual sand-rich HST and TST parasequences, and along LST:iv valley-margin stratal terminations.

AAPG Search and Discovery Article #90991©1993 AAPG Mid-Continent Section Meeting, Amarillo, Texas, October 10-12, 1993.