Unconventional Shale Gas Potential of the Floyd Shale in the Black Warrior Basin, Northwestern Alabama

Totten, Matthew W.¹, Albert S. Oko¹ (1) Kansas State University, Manhattan, KS

The commercial success of Barnett Shale gas production in the Fort Worth basin has drawn abundant attention to other potential unconventional shale gas formations. The Mississippian-aged Floyd Shale in northwestern Alabama has been previously identified as the probable source rock for conventional oil production in the Black Warrior basin. The results of this study suggest that it also represents a potential unconventional shale gas resource. Twenty-five samples from seven wells were analyzed for their clay-mineralogy, total organic carbon (TOC), thermal maturity, kerogen type, formation thickness and stratigraphic position based upon well logs.

Two distinct areas of prospective production were delineated. The first is in the shallower, northern portion of the basin where the Floyd Shale is encased by two dense limestone units, comparable to the stratigraphic relationship needed to contain induced fractures necessary to achieve production in the Barnett Shale. It is relatively thick (>200 ft), organic rich (>3.0% TOC), but thermally immature (<1.0% vitrinite reflectance). A second area within the deeper part of the basin has thicker, organic-rich shale (~300 ft; >3.0% TOC), which is also thermally mature (vitrinite reflectance >1.0%), but lacks the upper limestone-bounding unit.

Patterns of maturation and burial-history data indicate secondary cracking of original oil to gas in the deeper parts of the basin. Like the analogous Barnett Shale, potential production will require artificial stimulation. Production from the deeper portion of the basin could be challenging due to the absence of the upper limestone fracture barrier.