Print this pageSACROC Unit: An Integrated Approach to the Revitalization of a Mature Carbonate Reservoir
WINGATE, THOMAS P., ANTHONY J. BENVEGNU, CLAUD D. PICKARD, M. GHASEM BAYAT, AL M. REID and SUE TOMLINSON REID
The SACROC Unit (Kelly-Snyder Field) is the largest of the many prolific, Late Pennsylvanian carbonate buildups that comprise the Horseshoe Atoll. The reservoir is an isolated carbonate buildup consisting of successive stacked, shoaling-upward cycles. Cycles range from 20 to 70 feet thick with each capped by an exposure surface. Eleven major facies were described; (1) supratidal, (2) oolite shoal, (3) bioclastic shoal, (4) coated-grain, (5) reef, (6) algal meadow/mound, (7) shallow subtidal, (8) deep subtidal, (9) basin, (10) shallow water detrital and (11) deep water detrital. Generally, flow units are comprised of either a bioclastic shoal, shallow subtidal, and to a lesser degree reef or algal mound/meadow facies. Repeated subareal exposure of these facies created excellent secondary porosity and good permeability. Correlation of cycles across the Unit is difficult due to the lack of widespread shale markers and rapid lateral facies changes. Eighteen sequences ranging from Early Early Canyon to Middle Cisco age were identified based on fusulinids. This biostratigraphic framework made it possible to correlate individual sequences across the Unit. Canyon sequences are fairly thin, uniform in thickness and widespread across the Unit. Cisco sequences are thickest in the north and comprise all the pinnacle structures. Additionally, a series of Cisco age lowstand carbonate wedges were identified. Geologic and engineering data were used to build a three-dimensional model. This model improved the understanding of flow unit architecture within the reservoir.