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Abstract: Anatomy and Oil Recovery from Fluvial-Deltaic Reservoirs in the Cottage Grove Sandstone, Lake Blackwell Field, Central Oklahoma


Channel-fill and crevasse-splay or crevasse-channel sandstones form four separate oil reservoirs (zones A, B, C and D), in the Cottage Grove Sandstone (Osage-Layton sand), section 14, T. 19 N., R. 1 E., western Payne County. Net reservoir sandstones range in thickness from 16 ft to 6 ft having ten or more percent log porosity. Hydrocarbon-saturated thickness is commonly ten or fewer feet of sandstone. Entrapment is structural/stratigraphic; the reservoirs are located on a westerly-plunging anticline.

The discovery well was drilled to test the "Wilcox" sand, but was completed in the Osage-Layton sand in 1987, for 20 BOPD (43 degree API) and 7 BWPD, at 3,300 ft. Twelve development wells were drilled and completed in the four reservoirs between mid-1990 and mid-1993. Eleven were completed in zone A, two with no initial water and three with minor production of gas. Three other reservoirs (zones B, C, and D) produce from one well each. Two of the twelve wells penetrated reservoirs below oil-water contacts and one well completed in zones A and C has been abandoned because of high water cut. The more continuous reservoirs (A, B, and C) appear to benefit from a weak natural water drive. At least three structurally high wells flowed oil from zone A prior to the installation of pumps.

The four reservoirs had produced nearly 320,000 BO from ten wells by September 1995. We estimate that total recovery from the four reservoirs will be 421,000 BO by 12/31/2005, with no change in well status (base case). Reservoir simulation studies indicate that two options for management that will maximize oil recovery, using the same date (12/31/2005) for comparison. Recompletion of 7 wells, 6 of them in zone B, will improve oil recovery to an estimated 940,000 BO, or 223% of the base case. In addition, the drilling of four development wells, one to be completed in each of the four reservoirs, would provide for the recovery of an additional estimated 126,000 BO, or an additional 30%, compared to the base case.

AAPG Search and Discovery Article #90944©1997 AAPG Mid-Continent Section Meeting, Oklahoma City, Oklahoma