ABSTRACT: Geophysical Characterization and Petrographic Analysis of a Chesterian-Age Bioclastic Trap, Major County, Oklahoma

COFFEY, WILLIAM S., Marathon Oil Company, Oklahoma City, OK

Regional facies mapping of Chesterian age (Mississippian) carbonate buildups through the study area indicates a lenticular geometry of deposition. These carbonate "sands" have regional correlative dimensions of tens of miles in length with maximum thickness values up to 50 ft. This porous facies occurs at or near the Pennsylvanian/Mississippian unconformity and is overlain by a thick Morrowan age shale sequence. The base of this zone is characterized by an equally thick interval of interbedded tite limestones and shales. A series of northeast-southwest regional normal-faults present in this area creates enhanced porosity-permeability conditions proximal to fault boundaries, in addition to an added structural component to the trap.

The combination of faulting and thick velocity interfaces yielded excellent seismic recognition and characterization of this bioclastic trend. Information collected from the wellsite was input into a synthetic seismic model designed to simulate this carbonate buildup. The model supports this feature as a seismically observable phenomena. The bioherm is noted by a displacement of the overlying Morrow shale interval as an isochron thin over this buildup. Further, at maximum porosity development, a thickening of the wavelet occurs in the Morrow/Chester velocity interface. As porosity/foot values drop, this waveform develops a thinner peak.

Photomicrographic analyses of rotary sidewall cores from this interval provide a descriptive explanation of porosity preservation of this stratigraphic buildup and serves as the basis for the core/poster display.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)