Grammer, G. Michael1
(1) Western Michigan University, Kalamazoo, MI
ABSTRACT: Carbonate Slope Reservoirs: Insight from the Evaluation of Modern Slope Deposits in the Bahamas
Studies of modern carbonate slopes provide valuable insight into the sedimentary
processes, depositional architecture, and sequence evolution of equivalent subsurface
slope deposits. In these environments, reservoir potential results from the interplay
between paleogeographic orientation and geometry of the platform, mass flow depositional
processes, and early diagenetic modification.
In the marginal slope environment, coarse-grained talus deposits accumulate through rockfall processes in a strike-elongated but dip-foreshortened zone at the base of rimmed margins. Although areally limited, these deposits may have good reservoir or conduit potential, especially along windward margins, where they may not be covered by fine sediments derived from the bank top.
Further downslope, steeply-dipping proximal slope deposits consist of coarse-grained sediment deposited by a combination of rock-fall and grain flow processes. These deposits are formed during transgression and early highstand and are often characterized by a series of highly porous and permeable lenticular beds with preferential flow characteristics developed in a dip dimension. Proximal slope deposits, which may form along either windward or leeward margins, have high initial reservoir potential but may be adversely effected by extensive syndepositional cementation.
In the distal slope environment, reservoir potential is strongly dependent upon both highstand versus lowstand sedimentation, and the windward or leeward orientation of the margin. Extensive off-bank shedding of fine-grained sediment, especially along leeward margins, results in rapid lateral progradation through downslope deposition of a "highstand wedge". These large sediment wedges, however, have limited reservoir potential unless they are interbedded with coarser-grained turbidite and debris flow deposits.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.