Integrated Characterization of the Ordovician Utica/Trenton Organic-Rich Shale and Limestone Plays in New York State

Langhorne Smith¹, James Leone¹, and John Martin^2
1New York State Museum, Room 3140 CEC, Albany NY 12230, [email protected]
²NYSERDA, Albany, NY 12203

TOC data and log analysis show that there is up to 700 feet of organic-rich shale, calcareous shale and interebedded shale and limestone in the Indian Castle, Dolgeville and Flat Creek Formations and within the Trenton Group in central New York State. Together these are known as the Utica Shale play but as the array of Formation names suggests this is a somewhat complicated stratigraphy.

The Trenton Limestone grades laterally into the Dolgeville and Flat Creek Formations to the east. The Flat Creek Formation is composed of organic-rich argillaceous limestone and calcareous shale with TOC values up to 3% and thickens to the east to several hundred feet. The Flat Creek is time-equivalent to the middle part of the Trenton Formation. The Flat Creek is overlain by the Dolgeville Formation which is an interbedded limestone and shale that has TOC values up to 2% and time-equivalent to the upper part of the Trenton Formation. The interval with the highest organic richness in the Dolgeville can be traced westward into the Trenton Formation where it appears to maintain high levels of TOC, especially in the southern part of the State near where the Black River hydrothermal dolomite fields occur in the Southern Tier. This organic-rich interval in the Trenton may have potential for natural gas production.

The Trenton and Dolgeville Formations are capped by an unconformity called the Thruway Disconformity in the western part of the play area, which is easily recognized on gamma ray logs. The Disconformity is overlain by the Lower Indian Castle Shale which is the only unit in the Utica Shale sensu stricto that has a high enough organic content to produce gas. The Lower Indian Castle Formation is a fissile black shale that occurs at the base of the Utica in central New York that has TOC values up to 3%.

The Indian Castle Shale thickens across normal faults that were active during Utica deposition. The thickest accumulations of organic-rich Lower Indian Castle Shale are up to 400 feet. If coupled with the underlying Flat Creek, Dolgeville and intra-Trenton organic rich strata, the net thickness is as high as 700 feet in Delaware County to the east and over 400 feet across a large part of central New York. Burial depths range from zero at the outcrop belt in the Mohawk Valley to 9000 feet along the PA border. These strata are supermature and there are common gas shows in most wells drilled through the organic-rich intervals.

TOC values are 1-2% lower than in the overlying Marcellus, but the section of organic-rich strata is two or three times thicker. One of the biggest remaining questions is the impact of interbedded limestones and carbonate content of the shales on the play. Some of the limestones are also organic-rich and it is not currently understood if they will contribute to production.

AAPG Search and Discovery Article #90095©2009 AAPG Eastern Section Meeting, Evansville, Indiana, September 20-22, 2009