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