Ernest A. Mancini1
(1) The University of Alabama, Tuscaloosa, AL
Abstract: Variability in components of the Upper Jurassic Smackover Petroleum System, Northeastern Gulf of Mexico
The Upper Jurassic Smackover petroleum system of the northeastern Gulf of Mexico includes microbial carbonate mudstones as source rocks, shoal grainstones and packstones and microbial boundstones as reservoir rocks, anhydrites as seal rocks, syn-rift evaporites and post-rift siliciclastics as underburden rocks and post-rift siliciclastics, carbonates and evaporites as overburden rocks. The petroleum trap is combination structural and stratigraphic (depositional lithofacies, diagenetic facies, unconformities, or pinchouts) or structural (salt pillows, anticlines and diapirs, extensional fault traps associated with salt movement, or paleotopographic basement features). Anhydrites constitute the seal for the petroleum trap. Porosity includes primary interparticle and shelter and secondary grain moldic, intercrystalline dolomite, vuggy and fracture. Kerogen is typically microbial and amorphous; however, in the Manila sub-basin herbaceous kerogen is abundant. In basinal areas, underburden rocks are Louann evaporites, and updip the Louann Salt is absent. Siliciclastics constitute much of the overburden rocks in the basinal areas; however, a thick evaporite section occurs landward along the Wiggins Arch. Source rocks exhibit thermal alteration indices (TAI) of 2- to 4. Generation of oil is initiated at a level of maturity of 2 TAI in the Early Cretaceous, and expulsion and migration continued into the Tertiary. Heat flow is highly variable in the region. Oil generation commenced at depths of 8,000 to 11,000 feet. Updip oils, sourced locally, are low gravity crudes, and downdip hydrocarbons, sourced into deep reservoirs, include condensate and thermogenic gas. An understanding of the variability in the components of the Smackover petroleum system is important in designing a successful exploration strategy.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana