ABSTRACT: The Maurice Field: New Gas Reserves from Buried Structure along the Oligocene Trend of Southwestern Louisiana

Michael P. Prescott

Significant new gas reserves have recently been discovered in the Marginulina texana sands along the Oligocene trend at the Maurice field. Detailed subsurface maps and seismic data are presented to exhibit the extent and nature of this local buried structure and to demonstrate future opportunities along the Oligocene trend.

Since discovery in 1988, the MARG. TEX. RC has extended the Maurice field one-half mile south and has encountered over 170 ft of Marginulina texana pay. Estimated reserves are in the order of 160 BCFG with limits of the reservoir still unknown. This reserve addition would increase the estimated ultimate of the Maurice field by over 70% from 220 BCFG to 380 BCFG. Cross sections across the field depict the new reservoir trap as a buried upthrown fault closure with an anticipated gas column of 700 ft.

Interpretation of the origin of this local structure is that of a buried rotated fault block on an overall larger depositional structure. Detailed subsurface maps at the Marginulina texana and the overlying Miogypsinoides level are presented. These maps indicate that one common fault block is productive from two different levels. The deeper Marginulina texana sands are trapped on north dip upthrown to a southern boundary fault, Fault "B." The overlying Miogypsinoides sands are trapped on south dip downthrown to a northern boundary fault, Fault "A." The northern boundary fault, Fault "A," was the Marginulina texana expansion fault and rotated that downthrown section to north dip. Because of the difference in dip between the two levels, the apex of the deeper Marginulina texana fault cl sure is juxtaposed by one mile south relative to the overlying Miogypsinoides fault closure.

Analysis indicates that important structural growth occurred during Marginulina texana deposition with a local unconformity covering the apex of the upthrown fault closure. State-of-the-art reconnaissance seismic data clearly exhibit this buried rotated fault block. Occurrences of similar buried structure are predicted along the Oligocene trend offering explorationists many opportunities for additional natural gas reserves for the nineties.

AAPG Search and Discovery Article #90999©1990 GCAGS and Gulf Coast Section SEPM Meeting, Lafayette, Louisiana, October 17-19, 1990