Facies relationships, reservoir assessment and surface-to-subsurface correlation of the middle Bloyd formation (Pennsylvanian), North-Central Arkoma Basin, Arkansas.

摘要

The Pennsylvanian Morrowan succession in the subsurface of the Arkoma Basin is poorly defined stratigraphically, particularly correlation with respect to the informally named middle Bloyd sandstone of the outcrop belt. The unit is not well known in the eastern and southern portions of the basin, because of its braided stream environment and facies change to the Woolsey shale to the west in outcrop. The middle Bloyd sandstone overlies the Brentwood Limestone, while the equivalent of the middle Bloyd sandstone in subsurface is the Cannon sand, an important reservoir in the White Oak gas field. The Cannon sand is abundant in the eastern half of the subsurface study area, but disappears as one goes west, while the Brentwood limestone is not present in the subsurface east, but only appears in the west. The two units are not facies of each other.The Cannon subshale is recognized as an interval of shale directly beneath the Cannon sandstone or Brentwood limestone, whichever is present. The Brentwood limestone interval in outcrop is alternating limestone and shale beds that undergoes a facies change to all shale in the eastern subsurface study area, and is represented by almost all limestone in the western portion of the study area. The Cannon sandstone is the partial marine equivalent of the middle Bloyd sandstone, and either pinches out as one travels west in the subsurface, or more likely is the facies equivalent to the Woolsey shale in the west. The Dye shale overlies the Cannon sandstone or Brentwood limestone, whichever is present, as a blanket shale, both in outcrop and subsurface. The Woolsey Shale (not separated from the Dye Shale in this study) is the facies equivalent of the middle Bloyd sandstone.