Delineating and quantifying depositional facies patterns in carbonate reservoirs: Insight from modern analogs

Modern carbonate settings have long been used as analogs for interpreting various environments of deposition in subsurface data sets based on well-log and core data and have provided examples of how these environments can be interrelated within a larger context. This study focuses on carbonate sands in the Exuma Islands part of the Great Bahama Bank to show how modern settings can be better used for reservoir analogs by emphasizing visualization and quantification techniques that conceptually delineate aspects of potential grainstone reservoir distribution and heterogeneity. Along the windward margin of the Exumas, the association of tidal deltas, channels, and islands forms an exploration-scale linear belt of mostly ooid sand, approximately 5–10 km (3.1–6 mi) wide and 170 km (106 mi) long, paralleling the platform margin but set back from the platform edge. The distribution of carbonate sands in the Exumas was assessed with a digital elevation model and satellite imagery. By selecting different water-depth intervals, parts of the sand belt were highlighted for visual analysis and extracted for measurements of size and shape. For example, 37% of the sand belt comprises shallowest sands in which the largest areas, greater than 100,000 m2 (1.07 million ft2), are highly sinuous and maintain connectivity. The sand belt was also subdivided into various depositional settings; flood-tidal delta lobes comprise 85% of the sand belt. Tidal channels and islands add further heterogeneity to the sand belt. Channels average about 3 km (1.8 mi) in length and have regular but locally variable spacing. A representative island shows how the syndepositional topography of Holocene ridges develops complexly around antecedent Pleistocene topography.