SLATT, R. M., H.A.AL-SIYABI, C.W. VAN KIRK, and R.W. WILLIAMS, Colorado School of Mines, Golden, CO

Abstract: From Geologic Characterization to 'Reservoir Simulation' of a Turbidite Outcrop, Arkansas, U.S.A.

Detailed correlation of several outcrop exposures and subsurface cores of the Jackfork Group in the DeGray Lake area,Arkansas, has provided a 3D geologic model of a mile-long, steeply-dipping turbidite succession that is separated into two blocks by a strike-slip fault. The model was scaled-up into four stratigraphic zones, and net/gross and thickness were determined for each. By choosing the present day topographic ground surface as an unconformity top-seal and a lower topographic elevation as an oil-water contact, this outcrop can be considered a turbidite "reservoir."

Reservoir performance simulation was conducted using GeoQuest's ECLIPSE program in 3D, 3-phase black oil mode. Reservoir parameters were input into a 4-layer, 1936 cell model (100 x 200 ft. cells). Fault and stratigraphic zone boundaries were assigned zero transmissibility.

Drilling scenarios simulated for both water drive and depletion drive cases included single vertical wells in each fault block through the crest of the 'structure' and on the flank with the most permeable zone, and horizontal wells that penetrated all four zones. Water drive simulations produced more oil than depletion drive simulations. In both cases, the least amount of oil was produced from the vertical wells drilled on the crest of the structure, even though those wells drained the most areally extensive zone. More oil was produced from a thinner, more permeable flanking zone as well as from the horizontal wells.

The results demonstrate the ability to simulate outcrops when a sufficient 3D geologic characterization is available.When standing at the outcrop on the 'oil-water contact', the following points can be illustrated: (1) drilling the crest of a structure may not produce the largest volume of hydrocarbons; (2) vertical wells targeted to penetrate strata with the best stratigraphically-controlled reservoir quality can be more productive than wells targeted for the thickest strata; (3) horizontal wells can be more productive than vertical wells in reservoirs with steeply dipping strata.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England