INTERPRETATION OF SMALL SCALE GEOLOGIC FEATURES IN PENNSYLVANIAN THROUGH CAMBRIAN RESERVOIRS OF THE BLACK WARRIOR BASIN UTILIZING FORMATION MICRO-IMAGER LOGS

During the Summer and Fall of 2011, a 1498 m (4915 ft) stratigraphic test well was drilled at Gorgas coal-fired power plant in Walker County, Alabama. Pennsylvanian through Cambrian sedimentary rocks were characterized for potential CO₂ sequestration using wire line logs, a vertical seismic profile, and core samples. FMI data were interpreted using Schlumberger’s Techlog package. Formation MicroImager (FMI) logs have proven particularly useful for interpreting small scale geologic subsurface structures. Bedding, cross bedding, natural and induced fractures, faults, erosional surfaces, and borehole breakouts are all clearly visible. Understanding fracturing and faulting in key formations is of particular importance, both for the identification of potential leakage pathways for sequestered CO₂ as well as the contribution to our understanding of the evolution of the basin’s stress state through time. Though the entire well has been interpreted, particular emphasis has been placed on the principle formations targeted for sequestration, namely the Boyles Sandstone of the lower Pottsville Formation, the Hartselle Sandstone, Tuscumbia Limestone, and Stones River Group. Overall, the fractures are sparsely distributed within the targeted formations and display a generally northwest-southeast trend, consistent with regional northwest-southeast faulting and fracture patterns in the Black Warrior Basin of Alabama. The Boyles and Hartselle Sandstones exhibit minimal fracturing due to the friable nature of the sandstones. The Tuscumbia Limestone and Stones River Group show higher degrees of fracturing with more prominent fractures within dolostone at the base of the latter due to the more brittle nature of the carbonates. The relatively low number and wide distribution of the fractures suggests that they have little impact on the formational integrity with regards to sequestration. The results from this study will be incorporated into a larger regional study that will explore the evolution of the western extent of the Alleghanian Orogeny.