Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Geologic Assessment of Undiscovered Hydrocarbon Resources in the Jurassic Norphlet and Smackover Formations of the U.S. Gulf Coast
(1) U.S. Geological Survey, Denver, CO.
The U.S. Geological Survey (USGS) recently completed an assessment of undiscovered technically recoverable oil and gas resources in Jurassic and Cretaceous strata of the onshore coastal plain and State waters of the U.S. Gulf Coast. Assessment methodologies include detailed characterization of hydrocarbon source rocks (e.g. source rock maturation and hydrocarbon generation and migration), reservoir rocks (e.g. sequence stratigraphy and petrophysical properties), and hydrocarbon traps (e.g. trap types, timing of trap formation, and seals).
Assessments were completed for the Late Jurassic Norphlet and Smackover Formations. The Norphlet Formation is composed of sandstones and interbedded shales and siltstones that were likely deposited during the initial phase of a marine transgression. In central Mississippi, southwestern Alabama, and westernmost Florida, the Norphlet was deposited in alluvial fans, fluvial systems, and dune and clastic sabkha environments. Hydrocarbon source rocks for the Norphlet Formation are the lower mudstones of the Smackover Formation. For the USGS assessment, the Norphlet Formation was divided into three assessment units (AUs): the Norphlet Salt Basins and Updip AU, the Norphlet Mobile Bay Deep Gas AU, and the Norphlet South Texas Gas AU.
The Smackover Formation is one of the most important packages of Gulf Coast rocks. The lower part of the formation is one of the Gulf of Mexico basin’s major source rocks, and the porous part of the upper formation is a reservoir rock for many fields that rim the northern margin of basin. The lower part of the Smackover Formation is primarily composed of dark carbonate mudstone and argillaceous limestone formed in low-energy environments. The upper part is predominantly composed of grain-supported carbonates that were deposited in high-energy shallow-water environments. For the USGS assessment, the Smackover Formation was divided into four AUs: the Smackover Updip and Peripheral Fault Zone AU, the Smackover Salt Basin AU, the Smackover South Texas AU, and the Smackover Downdip Continuous Gas AU.
All AUs, with the exception of the Smackover Downdip Continuous Gas AU, were quantitatively assessed. Although the Norphlet and Smackover Formations have been extensively explored and produced, these strata probably still contain significant volumes of undiscovered oil and gas resources.