DELINEATION AND CORRELATION OF THE UTICA GROUP IN NEW YORK STATE USING A WELL LOG CLUSTERING ANALYSIS PROCEDURE

The Utica Group is an organic-rich shale deposited during the Late Ordovician. It is currently being extensively investigated to determine its viability as a major economic reservoir for natural gas in New York State. The Utica extends beneath a large portion of New York State. It is also present in Ohio, south-eastern Canada, Pennsylvania, West Virginia, and small portions of Kentucky and Tennessee.The intent of this project was to differentiate, correlate, and determine changes in thickness as well as depth of the four formations (Flat Creek, Dolgeville, Lower Indian Castle, and Upper Indian Castle) that comprise the Utica Group within the southern tier of New York State. Data used were well log, core, and outcrop. In order to identify formations within the Utica Group, the following well logs were used: gamma ray (GR), bulk density, neutron, photo-electric factor (PEF), sonic (DT), and resistivity. These data were analyzed within a software program (GAMLS) that permits a probabilistic cluster analysis using multiple well logs as clustering variables. Samples with similar log signature in multidimensional clustering space (electrofacies) are here termed a “mode” and the modes are treated as rock types. These interpreted rock types are then used to delineate and correlate the formations between wells. Although the clustering analysis procedures aid with delineation of the four formations within the Utica Group, we found that study of individual well log curves, particularly GR, PEF, DT, and resistivity, is useful to clearly identify the likely positions of the contacts. Also, a particular technique, the delta log R technique (Passey, et al., 1990) was used to help understand the effect of variable TOC content on well log signature. For example, the Flat Creek and Lower Indian Castle Formations were identified in part by the relatively high amounts of TOC in each formation. Correlations between wells agree with previous studies that the Flat Creek, Dolgeville, and Lower Indian Castle Formations pinch out (grade laterally) into the Trenton Group in the western portion of the study area.