Depositional, Structural, and Sequence Framework of the Gas-Bearing Cleveland Formation ...Western Anadarko Basin, Texas Panhandle

ow-permeability ("tight") reservoir sandstones of the lower Missourian Cleveland formation produced more than 435 billion cubic feet (Bcf) of natural gas through December 1990, mostly from Ochiltree and Lipscomb Counties in the northeastern Texas Panhandle. Although large-scale gas production started in1956, the regional stratigraphic, depositional, and structural setting of the Cleveland is poorly known. This report summarizes findings of a study conducted in a 5,100-mi2, 7-county area in the western Anadarko Basin using log suites from more than 860 evenly spaced wells, 4 cores from 4 wells, and numerous lithologic sample logs. The Cleveland formation, a subsurface unit in the study area, is well defined by regionally continuous, thin, radioactive, black shale marker beds that bound the unit. Most facies, including reservoir rocks, of the dominantly siliciclastic Cleveland formation accumulated as a series of eastward-prograding deltas consisting of prodelta, distal delta-front, and proximal delta-front deposits (in ascending sequence). Locally, sandstone-rich distributary channels incise delta-front facies. A regional fluvial system occurs in one stratigraphic zone in the middle to upper Cleveland throughout most of the study area and also composes reservoir rock. Four dominant sandstone trends exist in the producing area: three north-south-oriented, arcuate thicks consisting of stacked delta-front facies at inferred stabilized paleoshoreline positions and one east-west trend representing superimposed fluvial-channel incision after a pronounced drop in regional base level. Distinctive formation-thickness trends help document Cleveland paleophysiography and provide evidence of syndepositional faulting, flexure, and differential subsidence that markedly affected relative sea level. The unit thickens eastward toward the deep Anadarko Basin and reaches a maximum thickness of about 590 ft in southwestern Hemphill County. Depositional patterns were controlled by (1) a paleohigh in the west part of the study area (east flank of the Cimarron Arch) that separates siliciclastic facies from carbonate-dominated Cleveland of the Kansas Shelf, (2) subsidence of two subbasins within a northwest-trending half graben bounded by a syndepositional fault system on its south edge and a monoclinal flexure to the north, and (3) an irregular (stepped) depositional shelf controlled by differential subsidence of an underlying Oswego limestone buildup. The Desmoinesian Oswego limestone and Marmaton Group (undivided) and the Missourian Cleveland and Kansas City Formations were examined in the context of their sequence stratigraphic framework. Parasequences of the component systems tracts were correlated only for the Marmaton Group (undivided) and the Cleveland formation. This mostly siliciclastic interval can be subdivided into three sequences, at least one of which (Marmaton Group [undivided]/lower Cleveland formation) is bounded by type 1 sequence boundaries. The Marmaton Group siliciclastics are inferred to form a lowstand systems tract (prograding coastal wedge) and overlying transgressive systems tract in the study area; a regionally prominent marine-condensed section (black radioactive shale) caps the Marmaton interval. The Cleveland formation, the focus of the study, contains 10 parasequences (P) in the study area: (1) PI-P3 compose a progradational parasequence set of seaward-stepping deltaic facies deposited during a highstand of relative sea level, (2) P4, the middle Cleveland fluvial deposit, is a lowstand systems tract incised-valley fill that extends eastward beyond the inferred Cleveland depositional shelf break, (3) P5 and P6 are landward-stepping deltaic facies of a transgressive systems tract, and (4) P7-P10 consist of several thin, relatively poorly defined systems tracts. Source areas for all Marmaton and Cleveland systems tracts in the study area were to the northwest to southwest. Syntectonic effects and eustatic variation profoundly influenced late Paleozoic sedimentation in the western Anadarko Basin, although their respective control on relative sea-level change is not clearly resolvable.