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Cores taken along strike and dip transects through the Baptiste Collette crevasse splay, modern Mississippi River Delta, have been analyzed to determine the sedimentologic nature and potential reservoir quality of modern crevasse splay sands. Internal geometry, lateral and vertical continuity, and sedimentary characteristics were determined to construct a model of crevasse splay depositional systems applicable to hydrocarbon exploration.
The stratigraphic framework is more complex than previously recognized. This is demonstrated by the presence of several fine-grained (61-125µ) sand bodies (1-2 m or 3-6 ft thick) reflecting deposition in three distinct environments. Subaerial levee sands, which thicken toward the proximal end of the splay, contain 50-80% fine-grained (88µ) sand, 10% interlaminated muds, and 5-25% rooting. Distributary-mouth bar and point bar deposits (2 m or 6 ft below mean sea level) are 50-60% fine-grained sand (88µ) and 40-50% interlaminated mud, with 5% cross-bedding and a gradational base. The deeper (below 6 m or 18 ft) channel sands are 80-95% fine-grained (99-125µ) sand, with 20-75% cross-bedding, 10% interlaminated muds, and an erosional base. These correlatable sands are ncased in thick, organic-rich, bioturbated, bay and abandoned channel muds forming an impermeable seal.
Channel sands have the greatest reservoir potential, being more laterally continuous along dip, clean (< 5% silt and clay), well sorted, fine grained, and more homogeneous with few permeability barriers (i.e., mud layers and laminae). Conversely, the shallower bar and levee deposits have poorer reservoir quality, being less clean, less continuous laterally along dip, and with more permeability barriers.
This study should complement the limited knowledge of modern crevasse splay systems as well as provide insight into the exploration or enhanced recovery of hydrocarbons in ancient equivalents, such as the Admire 650-ft sandstone of Kansas.
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