DEVELOPMENT OF UPPER JURASSIC MICROBOLITE BUILDUPS IN THE LITTLE CEDAR CREEK AND BROOKLYN FIELDS AND POSSIBLE EMBAYMENT WIDE MICROBOLITE BUILDUPS IN SOUTHWEST ALABAMA

This study investigates the stratal relationships of a pure microbolite within the Smackover Formation at the Little Cedar Creek Field (LCCF), and Brooklyn Field for improved understanding of the development of Upper Jurassic reefal buildups in the eastern Gulf Coast. During the Jurassic, southwestern Alabama was divided by Appalachian ridges into three sub-basins: the Conecuh Embayment, Manila Embayment, and the eastern extension of the Mississippi Interior Salt Basin. The LCCF and Brooklyn Field are located in the Conecuh Embayment of southeastern Conecuh County, Alabama, and are the largest oil fields discovered in the state of Alabama. Production from the fields is currently over 27 million barrels of oil (Bbl) and over 29 billion cubic feet of gas (bcf). The microbolite buildups at LCCF and Brooklyn Field are known to have formed in an inner ramp setting during the Upper Jurassic (Oxfordian).

Deposition in the proto-Tethys during the late Jurassic includes extensive reefal buildups. Upper Jurassic microbolite structures are associated with both normal marine reef-building fauna and restricted marine settings. Previous studies of Smackover microbolite buildups determined that their occurrence was strongly controlled by paleotopographic highs.

The LCCF and Brooklyn Field are anomalous compared to previous studies of Smackover buildups in the eastern Gulf Coast, which concluded that microbial nucleation occurred on Paleozoic crystalline basement highs where depositional fabrics were heavily modified by dolomitization. Instead, the LCCF and Brooklyn Field microbolite buildups developed on mudstone facies, having no apparent association with paleo-highs, and having retained a large percentage of primary depositional fabrics.

In order to refine conceptual models of the controls on microbial nucleation, this study examines the basal contact of the microbolite through integration of well logs, well core, and petrographic analysis. In the process, it is also comparing differences in reservoir facies between the established Little Cedar Creek Field and newly drilled Brooklyn Field. Results from this study will enhance development of a model that incorporates depositional and diagenetic settings for the region.