South Lake Arthur Field and Occurrence of Buried Structures Along Oligocene Trend of Southwestern Louisiana

Michael P. Prescott

Significant gas reserves have recently been discovered in the Miogypsinoides sands along the Oligocene trend at the South Lake Arthur field. Detailed subsurface maps and seismic data are presented to exhibit the extent and nature of this local structure and to demonstrate future opportunities along the Oligocene trend.

Since discovery in 1980, the South Lake Arthur field has been extended 3 mi northeast and has encountered over 200 net ft of Miogypsinoides pay. Estimated reserves are 1,500 bcf of gas, with limits of the field still unknown. Cross sections across the field depict the trap as a buried anticline with a gas column approaching 1,000 ft.

Interpretation of the origin of this local structure is that of diapiric shale with a probable salt core. Detailed subsurface maps at the Miogypsinoides level and the overlying Camerina level are presented. These maps indicate the deeper Miogypsinoides is a simple faulted anticline while the overlying Camerina is highly faulted. The apex of the overlying Camerina structure is juxtaposed by almost 2 mi relative to the deeper Miogypsinoides structure.

Important structural growth occurred after Miogypsinoides deposition, with a local unconformity covering the apex of the structure. Deposition of the overlying Camerina strata was rapid, with faulting dying with depth in the underlying shale. State-of-the-art reconnaissance seismic data clearly exhibit this prolific buried structure. Occurrence of similar juxtaposed buried structures is predicted along the Oligocene trend, offering explorationists many new opportunities.

AAPG Search and Discovery Article #91036©1988 GCAGS and SEPM Gulf Coast Section Meeting; New Orleans, Louisiana, 19-21 October 1988.