Part 2 includes imagery, descriptions, and brief background information for several key carbonate areas (Figure 1A-1D) that cover a broad spectrum of shallow-water depositional environments. The images illustrate the geologic framework in modern carbonate environments and thereby graphically depict the geologic characteristics expected in ancient carbonate settings. The geologic framework is important at the reservoir scale where lateral variation of porosity and permeability, i.e., reservoir quality, is commonly tied to facies changes, and facies dimensions are required as input to reservoir models. The geologic framework is essential at the exploration scale for stratigraphic play concepts, which are related directly to depositional facies patterns.
As discussed by Harris (1989), the study of modern carbonate environments provides valuable information to aid subsurface interpretations at both the reservoir and exploration scale by lending predictability to unraveling subsurface facies patterns. Detailed studies of modern analogs suggest the following: (1) the trend and continuity of facies belts vary, but the patterns are ordered when the setting is understood; (2) typically, carbonate deposits form in localized ovoid or elongate thicks, not in widespread sheets; (3) the depositional systems contain complex, highly variable facies patterns in map view; (4) a predictable sequence of sediments, although not fully developed throughout the depositional environment, typifies the setting; (5) the stratigraphy as revealed by sediment coring is highly variable, recording a short-lived, but exceedingly complex, geologic history; and (6) early diagenesis related to evolving depositional environments can significantly alter the porosity and permeability of the sediments. Several of these points