Miocene sediments have yielded more than 3 billion barrels of oil from approximately 380 fields along the Louisiana Gulf Coast. Favorable sedimentary circumstances combine with a variety of structures to provide excellent conditions for accumulation.
The Miocene section is divisible into biostratigraphic units. Each unit possesses three distinct facies: updip a continental and near-shore massive sand facies, farther south an intermediate facies of alternating sands and marine shales, and downdip a deep-water facies of predominantly dark marine shales. Each biostratigraphic unit thickens downdip, the most pronounced thickening taking place seaward of the “hinge line” which separated the continental shelf and the continental slope at the time of deposition.
The Miocene strata dip regionally southward into the Gulf Coast geosyncline. Regional dip increases with depth to more than 800 feet per mile. It is interrupted by piercement salt domes, non-piercement or deep-seated salt domes, residual highs, and normal faults, all of which are related directly or indirectly to the plastic flow of sediments under gravity forces.
The Miocene sediments produce oil and gas in a belt basinward from the older Eocene and Oligocene producing trends. Within the subdivisions of the Miocene the production shifts to the south and east as the producing unit becomes younger. Most of the reservoirs are in the intermediate facies of alternating sand and marine shale. The stage of development of Miocene production becomes increasingly youthful toward the coast line and into the offshore province, which represents one of the largest concentrations of undrilled reserves in the world.