Regional Interpretation of the Late Ordovician Utica Shale Play in the Appalachian Basin
The Late Ordovician Utica shale was deposited in a foreland basin setting adjacent to, and on top of, the Trenton and Lexington carbonate platforms. Initial deposition of the Trenton and Lexington platforms began on the relatively flat Black River passive margin. Early tectonic activity from the Taconic orogeny created the foreland bulge that would become the Trenton and Lexington platforms. Carbonate growth was able to keep up with the overall rise in sea level while the areas between stayed relatively deeper until increased subsidence in the foreland basin lowered the ramps out of the photic zone and inundated the passive margin with fine grained clastics.
While the number of producing Utica wells is still low, there is sufficient data by which to construct a regional framework. Facies determinations from a regional data set of well logs helps identify the platform, slope, and trough facies. A regional sequence stratigraphic interpretation of the Late Ordovician succession allows for correlation between the carbonate platforms and through the trough. Sequences are identifiable as a series of transgressive and highstand systems tracts. Lowstand systems tracts are not commonly deposited on the platforms tops and often difficult to discern within the trough. Mapping the facies for each sequence over the complete succession shows the evolution of the basin. Facies modeling, when incorporated with core, XRD, and mineral models allow for reservoir prediction and the development of completions strategies.
Deposition and preservation of organic matter is directly tied to the sequence stratigraphic framework and facies. A geographically and stratigraphically extensive database of TOC measurements show a strong correlation when merged within the sequence stratigraphic framework with the highest amounts of present day TOC occurring in the lateral equivalents to the platform tops. Maturation patterns in the Appalachian basin have also been studied and the CAI has been mapped to identify different phases of hydrocarbons. Maturation patterns are strongly linked to present day depth of burial, although post-Alleghenian erosion must also be taken into consideration. The results strongly match the existing production. This regional framework incorporating existing well logs and geochemical data, when combined with a geologic model for the depositional history, has proven to be a useful tool in the early evaluation of an emerging play.
AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012