Abstract: Geological and Geochemical Evidence for Vertical Migration of Upper cretaceous Sourced Oils Into Tertiary Reservoirs: Winn and Grant Parishes, Louisiana

John B. Echols, R. K. Zimmerman, D. G. Goddard

Analyses of three Wilcox oils taken from the Colgrade Field (Carrizo sand reservoir), Bulger Creek Field (middle Wilcox sand reservoir), both in Winn Parish, and the Blue Lick Field (middle Wilcox sand reservoir) Grant Parish, Louisiana, correlate with other Gulf coast oils sourced from the Upper Cretaceous (probably Eagle Ford or Tuscaloosa). All three samples are mature and highly biodegraded. The oils from Blue Lick and Bulger Fields contain bisnorhopane (BNH), a Wilcox and younger biomarker in central Louisiana and southwest Mississippi. BNH was identified previously by the authors in chalk oil from Clark Creek Field, Wilkinson Co., Mississippi.

Previous studies project northeast-southwest wrench faulting (Boeuf River Fault) into the oil sample area. This faulting, and associated extensional fracture/fault and salt tectonism cause the conduits for vertical migration which emplaced the sampled oils into Wilcox reservoirs. The oils probably migrated from both the Eagle Ford/Tuscaloosa source beds and from fractured Austin chalk reservoirs breached by faulting.

The oils provide additional evidence that Wilcox and younger oil reservoirs of central Louisiana and southwest Mississippi were filled by vertical migration from Mesozoic source beds in contrast to long range lateral migration proposed by earlier workers.

The Central Louisiana Fracture Zone is described as an extensional fracture zone generated by wrench faulting. The trend of the zone coincides closely with that of the LaSalle Arch and is important in concentrating hydrocarbons along the arch. Exploration targets arise in all traps above Eagle Ford/Tuscaloosa source beds in the area.

AAPG Search and Discovery Article #90955©1995 GCAGS 45th Annual Meeting and Gulf Section SEPM, Baton Rouge, Louisiana