Our industry continues to become more reliant on geostatistics and reservoir simulation to provide critical information for sound business decisions. Spatial geostatistical analyses of modern systems provides insights into reservoir characterization for simulation. Spatial variograms from modern data sets can provide constraints and guidelines for spatial distribution of reservoir properties (porosity, permeability, saturation, etc.) that can significantly increase the accuracy of reservoir simulations.

Reefs and reef margins on carbonate platforms are well studied but the vast majority of reserves in oil and gas reservoirs are stored in platform interiors and, until now, our detailed knowledge of these systems was poor at best. Four modern isolated carbonate platforms from the Belize-Yucatan Province of Central America were studied. Each platform example represents different types of flow units and barriers common in carbonate fields. The results provide critical insights into models for reservoir flow unit architecture and heterogeneity.

Lighthouse and Chinchorro Platforms are grainstone-packstone dominated with abrupt facies partitioning and pronounced facies anisotropy and serve as models for high energy grainstone reservoir flow units. Glovers Platform interior is dominated by over 850 patch reefs surrounded by wackestone to grainstone sediments and serves as an example of a very heterogeneous isotropic flow unit.

Turneffe Platform is Characterized by mud dominated lagoons punctuated by channels and sparse patch reefs. Turneffe serves as an example of an intrareservoir barrier or baffle but highlights critical regions in reservoir flood situations where cross flow might be expected.

Chinchorro Platform provides a representative example of how this process works. Full platform analyses provides a set of anisotropy orientations and ranges that could be used to distribute properties of a single flow unit. Subdivision of the platform into subareas show distinctly different directional trends and also some differences in range characteristics. The importance is that it is an areally continuous data set that allows for unlimited variation in sample size for testing geostatistically significant spatial distributions of a variety of properties.

Structure plays an important role in determining facies architecture within some of these platforms which have been subjected to both extensional and transtensional tectonics. As models, these modern carbonate platforms provide valuable insight into how faulting within the platform can increase heterogeneity and anisotropy. With the application of high resolution 3-D seismic surveys and horizontal drilling these structure-reservoir facies relationships can be exploited for better reservoir management in newly discovered as well as mature fields.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah