Abstract

Much of the oil and gas production in the Main Pass and Breton Sound area of Louisiana state waters has come from Miocene-aged Cibicides carstensi (Cib Carst) reservoirs. While individual field sizes are relatively small, reservoir quality is typically excellent and the reservoir sands are found in well-defined north-south trending channels that are easily detected on 3D seismic data. Amplitude versus offset analysis also helps detect these channels and many undrilled and undeveloped seismic anomalies remain, although the relatively small size of the remaining traps and present-day economics based on lower gas prices means that they will likely not be developed anytime soon. Individual Cib Carst reservoirs have been classified as either CC, CC-1 (Upper and Lower members), CC-2, and CC-3 sands, representing several distinct depositional systems. The Cib Carst reservoirs are multi-lobed with several sand lobes separated by shale breaks that appear to act independently. In addition to vertical separation of the sand by shale breaks, there is considerable stratigraphic variation that separates the wells with the thickest, highest reservoir quality sand bodies, up to 200 ft (61 m) thick, in the center of the channel and thin, poorer quality sands at the channel edge. Most Cib Carst reservoirs show a considerable amount of pressure depletion with limited water drive support. This paper will present examples of Cib Carst fields with log, core, 3D seismic, and production history data, and then show some examples of the type of potential that remains.