Potential for Undiscovered Hydrocarbon Accumulations in Southern Louisiana – Insights from the Structural Interpretation and Restoration of 2D Seismic Lines

The U.S. Geological Survey recently completed a study focusing on the potential for undiscovered hydrocarbon resources in Tertiary strata of the onshore coastal plain and State waters of the U.S. Gulf Coast. The work includes interpretation of twelve two-dimensional seismic lines from southern Louisiana, which showed that structural traps for hydrocarbon accumulations may exist at depths below the current maximum depth of drilling. The potential traps, within Paleogene-Neogene strata, exhibit a wide variety of geometries that are similar to those currently being explored offshore in Federal waters. Structural modeling of the interpreted seismic lines show the large role that movement of the Jurassic Louann Salt played in controlling the structural evolution of the Louisiana Gulf Coast; all of the potential structural traps seen on the seismic lines are genetically related to salt movement. Structural restorations reveal that structures in the Paleogene-Neogene section formed soon after the sediments of each age were deposited. Kinetic and thermal models for source rocks in the Paleocene - Eocene Wilcox and Upper Cretaceous Eagleford Formations in the vicinity of the seismic lines indicate that oil generation may have occurred at depths between approximately 8,000 and 14,000 ft. If so, generation of oil from the Wilcox may have begun in some areas as early as the late Paleogene. The structural models therefore imply that Paleogene and Neogene traps may have formed early enough to receive a petroleum charge from Wilcox and Eagleford sources. Subsequent burial of these accumulations likely caused the cracking of oil to gas. Seismic interpretation combined with structural modeling indicates that undiscovered gas accumulations in southern Louisiana may be present at depths below some existing fields.