Oil in the Waltersburg sandstone of the upper part of the Upper Mississippian Chester series in the Eastern Interior basin occurs in diverse structural situations, not only on and near the crests of anticlines and the upthrown sides of faults, but also on unfaulted regional monoclines, low on the flanks of anticlines, and on the downthrown sides of faults. Waltersburg oil is trapped in a remarkable series of bar-like sandstone bodies, some entirely surrounded by shale. Though several processes may have joined in forming these bar-like features, petrographic and stratigraphic studies point to the deposition of their well sorted sands in a near-shore or shore-line environment by wave and current action. The near-shore facies extends beyond the area of commercial Waltersburg oil pools. Several hundred wells have been drilled to deeper horizons through Waltersburg sand bodies west of the productive region without encountering oil in the formation. As the productive Waltersburg region is almost co-extensive with the post-Pennsylvanian normal fault system of the southeast flank of the basin, the migration of oil along fault planes from lower sources may be in part responsible for accumulation in the Waltersburg lenses, though some occurrences can not be explained in this way. Two recent major Waltersburg discoveries have resulted from facies analysis through the projection of imperfectly known sandstone lenses into structural situations in which the lenses could act as oil traps.

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