Quantifying Facies Attributes of the Caicos Platform

Paul M. Harris¹ and Brigitte M. Vlaswinkel^2
1Chevron Energy Technology Company, San Ramon, CA
²Shell International E&P, Rijswijk, Netherlands

Spatial heterogeneity is a basic characteristic of carbonate depositional systems. Examining spatial depositional patterns and quantifying the facies attributes (e.g. size, shape, and facies interrelationships) in modern analogs can decrease uncertainty in a geologic model and therefore enhance the model’s utility. In an attempt to gather such valuable data, the attributes for key facies of the Caicos platform are assessed from a Landsat image through facies mapping. Reef-associated facies, including fully aggraded reef, partially aggraded reef, and apron are emphasized due to their importance in many isolated platform reservoirs.

Some key findings are:
1. Platform size and reef abundance are directly related, wherein reef (fully and partially aggraded) and reef apron occupy a smaller percentage of a large platform like Caicos.
2. Reefs seem to be patchier than aprons.
3. Fully aggraded reefs become somewhat wider as their length increases; partially aggraded reefs are discontinuous along their long axis so the relation to reef width is more subtle.
4. Reef width and apron width are directly related.
5. Probabilities can be set for expected dimensions for: reef width (10% probability that reef width > 410 m, 50% probability > 270 m, and 90% probability > 145 m); and apron width (10% probability that apron width > 945 m, 50% probability > 395 m, and 90% probability > 90m).

Modern analogs like Caicos can play an important role as conceptual facies models for characterization of a reservoir, and also in providing facies attribute information to be used as input in building reservoir models.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas