About This Item
Share This Item
Oil Creek Truncation Traps in Cooke and Grayson Counties, Texas: Abstract
One of the most prolific reservoirs in North Texas is the Ordovician Oil Creek Sandstone.
This discussion presents one of the types of entrapment from which this horizon produces. The basic principle of oil occurrence along an unconformity is universal, applying to oil fields and future exploration the world over.
The pre-Pennsylvanian section in North Texas is composed of an erratic basal Cambrian sandstone overlain by up to 5,000 feet of Cambro-Ordovician Ellenburger carbonates, the Ordovician Joins Limestone, and the Oil Creek Formation with its basal sandstone 40-60 feet thick. This is covered by 2,000-4000 feet of Pennsylvanian (Strawn and Canyon) clastics which are highly productive. Cretaceous rocks cover the surface, thickening from the erosional edge in northwestern Cooke County to 3,600 feet in southeastern Grayson County.
During the Wichita orogeny (post-Morrow-pre-Atoka) the Muenster arch was uplifted and severely eroded, furnishing clastic deposition on both sides of the arch. The Marietta-Sherman basin subsided and the Criner Hills uplift occurred. Pre-Pennsylvanian beds were eroded progressively deeper into the section until basement rocks were exposed on the highest portion of the Muenster arch.
It is postulated that the Strawn beds, which then covered the platform, furnished the source and seal for the Oil Creek production in the following examples: Ouachita and Arbuckle orogenies (late Pennsylvanian) rejuvenated earlier faulting on the platform, and this faulting partially controls the production.
Exploration is quite attractive, especially for independent operators.
Lease costs are about $10-$15/acre for 1- to 2-year leases except in the Walnut Bend areas where it ranges much higher. Mineral ownership is fairly simple, and 7/8 leases can usually be obtained. The productive areas are not large, hence large lease blocks are unnecessary. Drilling costs are nominal, a 5,000-6,000-foot dry hole costs $20,000-$25,000.
There are classic examples of oil occurrence in subtle stratigraphic traps directly related to an unconformity.
Geology alone will find more of these fields with no dependence on structural closure or geophysics. Careful log correlation is essential; a small fault in the Pennsylvanian section may indicate an untested fault block in the underlying Oil Creek.
The economic incentive is already established in excellent reservoirs. The Oil Creek of North Texas and the other Simpson sandstones of southern Oklahoma offer a fertile hunting ground for truncation prospects.
Acknowledgments and Associated Footnotes
1 Consultant, Wichita Falls
Copyright © 2006 by the Tulsa Geological Society