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Thickness and porosity trends of several lower Morrow sandstone units were strongly influenced by the paleogeomorphology of the subjacent Mississippian Chester limestone in a study area near Persimmon Creek field in T20N, R22W, southwestern Woodward County, Oklahoma. Pre-Pennsylvanian streams flowing south-southwest across the Anadarko basin shelf had created a dendritic drainage pattern with paleogradients of about 40 ft/mi (7.5 m/km), and intervening stream divides were 50 to 100 ft (15 to 30 m) above the valley floors. As the sea transgressed the area in the Early Pennsylvanian, cyclic transgressions and regressions led to deposition of four prominent lower Morrow sandstone members separated by shale units which are approximately parallel lithologic time markers.
The basal Hamilton sandstone is a prograding beach complex which strikes west-northwest, but the Chester paleotopographic surface has caused local thick sand deposits with good porosity to strike north-south along the paleovalleys; thinner accumulations occur above the paleodivides. The overlying Yellow sandstone, a delta-front complex that includes some shale units, demonstrates similar sand distribution characteristics. In the overlying Brown sandstone, also a delta-front complex, thickest sand accumulation and best porosity development occur above the Chester paleodivides rather than the paleovalleys, regardless of the genetic origin of individual sandstone beds. The uppermost Fritzler sandstone occurs only in the northwestern part of the study area and shows little relationship to Chester paleotopography.
Persimmon Creek field is a small stratigraphic-trap accumulation that occurs above a prominent southward-plunging nose or paleotopographic high on the Chester limestone surface. Four wells produce from two Brown sandstone units, a stream-mouth bar and an overlying channel sand which has prograded across the bar. Although the geometry of individual sandstone bodies such as these is almost impossible to predict prior to field development, Morrow sandstone prospects can be defined by locating the most likely sites of thick porous sand accumulation controlled by Chester paleotopography.
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