Factors Controlling Occurrence of Morrow Sandstones and Their Relation to Production in the Anadarko Basin

ABSTRACT Stratigraphic and lithologic data from 1200 wells in the panhandle areas of Texas and Oklahoma and 600 wells in northwestern Oklahoma were recorded in a form suitable for computer processing. Maps were prepared for each of three subdivisions of the Morrow in the Panhandle area and for each of seven operational units selected to subdivide the lower Morrow in northwestern Oklahoma. These isopach and quantitative facies maps showing a real variation in thickness and rock types were used in combination with detailed stratigraphic relationships based on electric log correlations to interpret the depositional history and predict areas most favorable for development of porous sandstones. In the panhandles of Texas and Oklahoma and in northwestern Oklahoma, the Morrow Formation is the basal transgressive predominantly clastic unit of the Pennsylvanian System, unconformably overlying the Mississippian. The upper boundary is delineated by the base of the Thirteen-finger limestone, an electric log marker, and the lower boundary by the Pennsylvanian-Mississippian contact. The thickness of lower Morrow sandstone accumulations correlates closely with the residual structure on the top of the Mississippian unconformity. This structure, a result of either topography or early Pennsylvanian structural movement, apparently existed before or developed during deposition of these units. Isopachous and structural data indicate continued activity of the structures throughout Morrow deposition. Distribution of coarse terrigenous clastics within the predominantly fine terrigenous clastic Morrow Formation suggests one source of sand west of the Panhandle area and a second source on the northeast. The Wichita-Amarillo uplift south of the depositional basin began to supply coarse clastic material during deposition of the upper Morrow unit. In the Panhandle area, widespread sheet sandstone and sandstone beds that parallel trends of early Morrow shorelines are interpreted to be nearshore marine sediments deposited as the early Morrow sea overlapped onto the shelf areas. The thin lenticular upper Morrow sandstone bodies are interpreted as having been deposited by a complex stream system flowing southeast toward the basin axis. Oil and gas production from the Morrow sandstones is primarily stratigraphically controlled and generally not related to local structural features. Topographic highs or structures that developed contemporaneously with deposition of these units controlled the development of sandstones and favored deposition of sandstones on the flanks or off-structural positions rather than on structural crests.