Stratigraphy and Source Potential of Smackover Formation in Northern Manila Embayment, Southwest Alabama

William J. Wade, Roger Sassen, Elizabeth W. Chinn

Petrographic studies of conventional cores and correlation of electric logs indicate that upper Smackover hydrocarbon reservoir facies are more widely distributed in the northern Manila embayment of southwest Alabama than previously recognized. The embayment does not appear to have been a separate basin during early Smackover deposition, but rather was an extension of the Mississippi salt basin. A carbonate shelf and starved basin topography developed in the Manila embayment during deposition of the Smackover Formation and is reflected in the distribution of Smackover lithofacies. Fine-grained clastics are abundant in shelf and back-shelf environments.

Source rock geochemistry of the Manila embayment appears to be atypical of the eastern Smackover trend because of a strong terrestrial influence. Although the upper Smackover is organic-rich, potential for generation of crude oil is limited by abundant terrestrially derived kerogen and by thermal immaturity. The updip lower Smackover nearest the paleoshoreline also appears to be characterized by terrestrial kerogen. Thermal maturity and source potential for crude oil in the lower Smackover increase southward. This helps explain the clustered distribution of crude oil discoveries downdip in proximity to the thermally mature lower Smackover source facies.

AAPG Search and Discovery Article #91042©1987 GCAGS and GC-SEPM Section Meeting, San Antonio, Texas, October 28-31, 1987.