REGIONAL DEPOSITIONAL TRENDS IN THE DEVONIAN GENESEO/BURKET BLACK SHALE BASED ON GAMMA RAY-DENSITY TRENDS

Open Access
Author:
Arnold, LaMichelle Andrea
Graduate Program:
Geosciences
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 14, 2010
Committee Members:
  • James Terry Engelder, Thesis Advisor
  • Terry Engelder, Thesis Advisor
Keywords:
  • organic matter
  • black shale
  • Geneseo
  • Burket
  • gamma ray
  • bulk density
  • thickness
Abstract:
ABSTRACT Gas shales are becoming increasingly important as new technologies are applied to enhance their production of natural gas. The Barnett, the Fayetteville, and the Haynesville have all been successful gas shale plays in North America. In addition, the Marcellus has recently stimulated a boom in Pennsylvania shale-gas production. The Geneseo-Burket is a Middle Devonian black shale of the Genesee Group that overlies the Tully Limestone and Hamilton Group, which includes the Marcellus Black shale. It is currently unclear whether it is prospective as a gas shale or not. This study seeks to examine the commercial value of the Geneseo-Burket Shale through the characterization of the relationship between density and organic matter. This relationship, in conjunction with thickness trends in a sequence stratigraphic framework, can be used as an exploratory tool for gas shale reservoirs in the Appalachian Basin. This study uses 280 well logs used to conduct a petrophysical evaluation of the Geneseo-Burket Shale in Pennsylvania and New York. Gamma ray and bulk density well logs, supplemented by well cuttings, are used to derive isopach/structure maps, density-gamma ray trends and the spatial distribution of organic matter. The relationships among these characteristics and the mechanisms that produce their regional patterns are also explored. Distinctive density patterns can be observed in well logs of the Geneseo-Burket throughout the basin. Density vs depth trends illustrate considerable deviation from normal shale sections. Observed lower densities in the Geneseo-Burket are a likely indicator of increased organic matter. Density data are compared with gamma ray logs to quantify the relationship between density and organic content. They are correlated with a Pearson product-moment correlation coefficient (R2) equal to 0.65. Organic matter percentages in the Geneseo-Burket are calculated and range from 2-18 percent by volume. An empirical relationship is developed to convert organic matter in volume percentages to total organic carbon in weight percent. The spatial distribution of organic matter is mapped and increasing concentrations in western Pennsylvania suggest a decrease in clastic dilution. Also, the variation in formation thicknesses is illustrated by construction of an isopach map. The Geneso-Burket extends throughout the northern Appalachian Basin and thicknesses exceed 150 feet in eastern Pennsylvania. The internal stratigraphy of the Geneseo-Burket is defined in terms of its well log (density, gamma ray) character. Locally, the interval is characterized by at least 4 gamma ray maxima and density minima that correlate. These patterns are repeatable throughout northern Pennsylvania and west-central Pennsylvania and ultimately demonstrate the extent and structure of the basin. Regional variations in the interval of the Geneseo-Burket are identified, defined and summarized into a depositional sequence, using a sequence stratigraphic framework. Finally, the distribution of systems tracts in the Genseo-Burket, Lodi limestone and Penn Yan Members of the Genesee Group suggest that these units are analogous to the Union Springs, Cherry Valley, and Oatka Creek members of the Marcellus Formation in Hamilton Group.