ABSTRACT

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 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 backshelf 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 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 contributes to explaining the clustered distribution of crude oil discoveries downdip in proximity to the thermally mature lower Smackover source facies.