DELINEATING THE UTICA FORMATION: FROM OUTCROP TO SUBSURFACE

Confirming the surface work done by Brett, Baird, Mitchell and Jacobi, the Utica can be subdivided into the upper and lower Indian Castle members, the Dolgeville and the Flat Creek Formations. Current research into the gas potential of organic rich shales has also established the different formations of Utica Shale by way of their total organic content.

The surface work done on the Indian Castle Formation by Baird and Brett, 2002 show in measured sections the approximate platform slope facies transition where the Steuben limestone is replaced by the Dolgeville closer to the platform. Due to the recent Black River Formation natural gas exploration in south central New York more logs suites have been run increasing the amount of data in the subsurface by 800 percent. The one member of the Trenton Formation that can be correlated in the subsurface with confidence is the Steuben limestone. Making an isopach map of this formation from subsurface tops, the Steuben limestone pinches out, and is being onlaped by the Dolgeville, the underlying Rust Formation then is onlaped by the Flat Creek. This can be demonstrated by cross sections using geophysical-wireline gamma-ray logs for correlation. The one top that is not easy to pick, is the Indian Castle. Confidence in this subtle gamma ray pick is due to the subsurface correlations done by Baird on twenty cores from our core repository that were taken throughout the Mohawk Valley during the early seventies. Baird's subsurface work has provided a good reference on subsurface thicknesses of these formations.

Another form of identification is the use of organic geochemistry. The Flat Creek has a total organic content range of 1.5%- 3.0%, the Dolgeville has a range between 1% -1.5 %, and the Indian Castle is usually less than 1.0%. These values have been derived from core and well cuttings. Using bulk density logs, increased organic content can be deduced with a decrease in bulk density. When used with the above logs, resistivity logs show an increase in the Dolgeville Formation and a larger increase in the Flat Creek Formation this would also confirm the abundances of organics in each formation.