DEFINING AND CORRELATING MIDDLE DEVONIAN STRATA INCLUDING THE MARCELLUS SUBGROUP IN THE SOUTHERN TIER OF NEW YORK STATE USING A WELL-LOG CLUSTERING ANALYSIS PROCEDURE

The Marcellus subgroup, the lower part of the Devonian Hamilton Group, is located in the subsurface of eastern Ohio, Pennsylvania, West Virginia, and the southern tier of New York. I have concentrated on the portion of the Marcellus located in south central New York. There, the Marcellus Subgroup is comprised of two formations. The older formation is the Union Springs, comprised of the Bakoven shale member, and the younger formation is the Oatka Creek, comprised of the Cherry Valley and Hurley limestone members and the Berne shale member. Well logs were analyzed using a probabilistic clustering analysis program (GAMLS: Geologic Analysis via Maximum Likelihood System) and used to define major lithologies. The shales and limestones in and around the Marcellus were used to pick the top and bottom of the Marcellus subgroup, and to correlate strata between wells. A core from the Beaver Meadows well in Chenango County contains most of the Marcellus section plus parts of the Devonian Onondaga limestone and Oriskany sandstone formations. Using GAMLS, I was able to correlate the top and bottom of the Marcellus plus lithologic breaks within the Marcellus that I observed in the Beaver Meadows core with the results of the clustering analysis. After making correlations among 32 selected wells within Chemung, Chenango, Steuben, and Tioga Counties, the results indicate that the Marcellus thickens and deepens to the southeast. This agrees with previously published isopach and structure maps. Details on correlation and thickness variations of the Marcellus subgroup formations are presented. The main result of this work is the demonstration of the ability to distinguish and correlate the formations within the Marcellus subgroup using the well log clustering analysis procedure.