The Distribution of Sediments on the Caicos Platform, B.W.I.: A Modern, High-Energy Isolated Carbonate Platform as a Guide to Understanding the Distribution of Enhanced Reservoir and Barrier Facies in Ancient Carbonate Reservoirs

Abstract

The Caicos Platform has been previously recognized as a high-energy, wave-swept, isolated carbonate platform and is an analog for ancient carbonate reservoirs on grain-dominated isolated platforms (e.g. Tengiz, Kashagan, and Karachaganak). The distribution of muddy tidal flats (potential barriers) and prograding dune/foreshore environments (grainy reservoir facies with favorable diagenesis) are important to modeling reservoir properties in these types of reservoirs. On the Caicos Platform, the lack of a reef tract along the eastern margin allows energy from easterly trade winds onto the platform resulting in the westward transport of sediment across the platform. Results of this include a relatively ‘starved’ and deep Central Platform Trough (maximum depth 8m) on the windward platform interior, significant accumulation of prograding dune/foreshore systems on shorelines that face into the trade winds (Long Bay Beach and eastern shoreline of West Caicos), and island accretion on the downwind side of the platform due to constant sediment supply (e.g. West Caicos Island). Sediment flux is also high after major storms when wave-dominated ooid shoal systems are disrupted and large amounts of sediment are transported across and off the platform (grainy reservoir target in slope). Large-scale muddy, peloidal, and microbial tidal flat environments are restricted to the leeward side of Pleistocene islands on the northside of Caicos Platform. Topography on the islands is primarily from carbonate eolianites. The distribution of tidal flat subenvironments is influenced by the wind-generated waves. Well-developed levees are observed facing the platform interior where wave energy was most direct. The levees create enough topography to influence drainage in the tidal flats and this disrupts the zoned pattern that is typically described as being a characteristic of humid tidal flat environments. In areas where the shoreline is protected from waves, due to the presence of remnant Pleistocene highs, levees are poorly developed and the tidal flats display a more regular zonation of subenvironments. Understanding of the processes and resulting sediment distribution on high-energy, wave-swept platforms from Modern environments is important to predicting the occurrence of enhanced reservoir properties, potential reservoir barriers, and potential exploration targets in ancient hydrocarbon fields where similar processes likely existed.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016