HYDROCARBON POTENTIAL OF THE FLOYD SHALE IN THE BLACK WARRIOR BASIN, NORTHWESTERN ALABAMA
Albert S. Oko,
Kansas State University, Geology Department,
An unconventional shale gas play is considered a fully self-contained petroleum system, whereby critical petroleum system elements, source, reservoir, and seal coincide in the same formation. This study investigated the Mississippian Floyd Shale in Northwestern Alabama which represents a potential unconventional shale gas resource in the Black Warrior basin. Although the Floyd has been previously identified as the possible source rock for conventional Mississippian oil production in the Black Warrior basin, evidence from geochemical measurements suggests that it has a potential for unconventional thermogenic gas production. Mineralogy consists of illite clays and predominantly silica and calcite. Production will require artificial stimulation as indicated by low permeability measurements. Two distinct areas of prospectivity were delineated based on straigraphic position and thermal maturity. First is the shallow northern portion of the basin where the Floyd Shale is enclosed by dense limestone units, relatively thick (>200 ft; >61 m) and organic rich (>3.0% total organic carbon), but thermally immature (<1.0% vitrinite reflectance). A second area corresponds to the deep part of the basin where the formation is thicker (~300 ft; 92 m), organic rich (>3.0 total organic carbon), thermally mature (vitrinite reflectance >1.0%), but lacks the top limestone bounding unit. Patterns of maturation and burial-history data indicate secondary cracking of original oil to gas in the deep parts of the basin. Production from the deep portion could be challenging due to absence of the top fracture barrier, but good engineering of completion techniques can aid the Floyd Shale play economics.
AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid