STERNBACH, CHARLES A., Shell Western Exploration and Produciton, Inc., Houston, TX

ABSTRACT: Trap Analysis: Case Study of Arbuckle Reservoir in Fault-Bounded Structure, Wilburton Field, Arkoma Basin, Oklahoma

Trap analysis has widespread application for prospect evaluation of fault-bounded closures in the Mid-Continent. Trap analysis involves detailed study of how the objective section is juxtaposed with the sealing section across a fault and can be used to predict prospect viability and potential hydrocarbon column heights for lower Ordovician dolomite objectives in faulted structures along the Marathon-Ouachita orogen.

In the Arkoma Basin, productive column height of the Arbuckle gas accumulation at Wilburton Field is substantially less than the mapped structural closure. Some gas in the upthrown Arbuckle Dolomite leaked into Simpson Sandstone on the downthrown side of the critical counter-regional fault and migrated away from the Arbuckle trap. Post-Simpson tight limestone and shale on the downthrown block sealed gas in Arbuckle Dolomite on the highest part of the upthrown block. A regional isopach map of the Simpson Sandstone indicates the minimum fault throw prospects need to juxtapose Arbuckle reservoir with the post-Simpson sealing section increases to the south. Not only can fault throws be too small, they can also be too large to seal. The Pennsylvanian Spiro Sandstone is a potential thief sa dstone for prospects in the Arkoma Basin with large fault throws. Viable prospects are constrained by a stratigraphically controlled window of fault throws consistent with trap analysis.

The deeper pool Arbuckle discovery at Wilburton field in late 1987 set off a drilling boom in the Arkoma Basin. Before and after Wilburton, many Arbuckle dry holes have been drilled with little regard for trap analysis. Many dry holes outside of Wilburton did not have proper fault throw on the critical trapping fault to juxtapose Arbuckle reservoir section with downthrown seal section. Trap risks can be evaluated prior to drilling with a good understanding of the structure and the rock properties of local stratigraphy.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.