ABSTRACT

The area of investigation is approximately 168 square miles in western Grady and eastern Caddo Counties, Oklahoma. It is on the west-central flank of the Anadarko Basin, a northwestward trending structural and depositional basin in southwestern Oklahoma where Paleozoic sediments reach a thickness of more than 35,000 feet. This investigation involves a stratigraphic analysis of the lower part of the Late Pennsylvanian (Missourian) Hoxbar Group, which attains a total thickness of 2,800 feet in this area.

The Hoxbar Group includes strata between the top of the No-Ho-Co "formation" and the base of Marchand. Major sandstone developments in this group are (in descending order): Wade sand, Hedlund sand, Medrano sand and Marchand sand. The Marchand sand is the only sand of economic importance to date in the area investigated.

The major objectives of this investigation were (1) to determine the geometry of the Marchand sand, (2) to reconstruct the paleodepositional environment of the sand; and (3) to determine the relative importance of structure versus stratigraphy in oil accumulation in the Marchand sand.

The Marchand sand appears to be marine offshore bars, the tops of which have been partially truncated during a still-stand or regression of the sea. Vertical and lateral variations in porosity and permeability in the reservoir rocks result in oil accumulation in upper, middle, lower and even multiple units within the sand. Structure exerts only minor effects upon accumulation; the trapping mechanism being essentially stratigraphic.

One probable source area of the Marchand sand is to the southeast where sediments were carried by longshore currents from tectonically active source lands within and along the eastern flanks of the Anadarko Basin. Other possible sources include the Wichita Mountains to the southwest, local growth structures such as the Cement anticline, and the shelf area to the northeast which may have been exposed to subaerial erosion intermittently in Early Missourian time.

The Marchand sand extends for more than 16 miles trending northwest-southeast. The first production in the area was discovered in 1967 in N. E. Verden Field. At the end of December, 1970, 45 wells were producing and by the end of May, 1971, 74 producing wells had been completed utilizing 160-acre spacing. The reservoir sand ranges in thickness from zero to 260 feet, the sand is undersaturated and the gas/oil ratios are approximately 700 to 1. Reserves for wells with thickest pay sections are more than 750,000 barrels of oil (Graff, 1971, p. 1687-88).

Similar stratigraphic trends may be presented in the upper units of the Hoxbar Group in the area investigated.