Examining Potential Reservoirs in the Paleogene, Southern Louisiana, USA

Abstract

To support a new hydrocarbon resource assessment of the Paleogene rocks in southern Louisiana by the U.S. Geological Survey (USGS), a regional stratigraphic and structural framework was constructed using 2D seismic, well logs and foraminiferal biostratigraphy. The proposed framework led to models of depositional environments and reservoir characteristics for potential undiscovered fields in an area previously estimated by USGS to contain a mean undiscovered conventional resource potential of 52.4 trillion cubic feet of gas and 1.9 billion barrels of natural gas liquids. Attempts were made to trace the extent and character of depositional fairways for potential reservoirs in the Paleocene-Lower Eocene Midway and Wilcox Groups; Middle Eocene Claiborne Group; and Oligocene Vicksburg, Frio, and Anahuac Formations. The framework correlates the lithostratigraphy and detailed biostratigraphy from type localities in Alabama to regional well-log cross sections in Louisiana that extend from north of the late Paleocene shelf edge in Evangeline and St. Landry parishes to well data from the southernmost onshore wells as of 2014. The upper Paleocene formations in Catahoula and Avoyelles parishes are productive from fluvial, deltaic, and near-shore marine shelf sandstones. In St. Landry and Evangeline parishes, these formations are productive from reservoirs deposited in the distal part of a fluvial-dominated delta. The cross sections indicate fairways for the deposition of continental-slope and basin-floor sandstones in the Midway and Wilcox Groups. There are also indications that thin slope and basin-floor sands were deposited during Claiborne and Vicksburg times. Upper Oligocene Frio and Anahuac Formation sandstones appear to be more robust and persistent throughout southern Louisiana. Structural interpretations showed fault blocks with minimal expansion where reservoirs were deposited in fluvial and near-shore marine shelf environments. Where reservoirs were deposited in fluvial-dominated delta environments, normal faulting is likely associated with allochthonous salt bodies and welds. The interpretations allow for trapping mechanisms for reservoirs identified in stable shelf and expanded fault-zone depositional and structural settings. In the Paleogene slope and basin floor, faulting may provide traps for hydrocarbons, or may be a risk for hydrocarbon leakage.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015