ABSTRACT: Analogues for Understanding Flow Unit Heterogeneity from the Isolated Platforms of the Belize-Yucatan System
Lomando, Anthony J.1 and Eberhard Gischler2
(1) Chevron overseas Petroleum, San Ramon, CA
(2) Geologisch-Paläontologisches Institut der Universität
The closely spaced, isolated carbonate platforms: Glovers, Lighthouse, Chinchorro and Turneffe, along the eastern Yucatan margin; are significantly different with regard to sedimentary facies architecture, especially in platform interiors. Intra-reservoir scale structure, differential subsidence, oceanic exposure and erosion have played an important role in setting up facies templates. These provide a range of reservoir flow unit and baffle/seal analogues that can be applied in both qualitative and quantitative fashions. Glovers Reef has a deep lagoon with 860 more or less randomly distributed patch reefs surrounded by lagoon-floor wackestones representing a very heterogeneous flow unit. Linear trends or belts of grainstones, coalescing patch reef boundstones and muddier, slightly deeper lagoons, characterize the interiors of Lighthouse and Chinchorro platforms. Facies asymmetry in the platform interiors is common; skeletal dominated on the windward sides and peloid-rich on the leeward sides. These higher-energy platforms provide insight into the degree of lateral heterogeneity and anisotropy within platform interior flow unit systems and are modeled with the use of spatial semivariograms. Turneffe Islands has large, protected interior lagoons that are surrounded by large land/mangrove areas. Lagoons have restricted circulation and are devoid of coral patch reefs or grain-shoals and dominated by organic-rich wackestone. Turneffe, as an analogue, demonstrates the regions and degrees of cross-flow and vertical communication that should be expected across intra-reservoir barriers and baffles. The size range of these platforms is similar to many Tertiary to Paleozoic reservoirs and examining the diversity of reservoir analogues within these platforms provides many useful reservoir lessons.
AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia