Semester

Fall

Date of Graduation

2010

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Geology and Geography

Committee Chair

Timothy R. Carr.

Abstract

In the central Appalachian basin, the Middle Devonian organic-rich shale interval, including the Marcellus Shale, is an important target for natural gas exploration. It has emerged as a giant unconventional resource play due to aerial extent and potential for individual wells to produce large volumes of gas. The Marcellus Shale is well studied on the surface without the incorporation of the subsurface stratigraphy. However, to fully understand the Marcellus economic potential it is important to investigate and map the related Middle Devonian sub-surface stratigraphic units. The interval studied includes the Onondaga Limestone (Eifelian), Marcellus Shale (Eifelian), Purcell Limestone (Eifelian), Mahantango Shale (Givetian), Tully Limestone (Givetian), and Harrell Shale (Fransnian-Givetian). The first goal of this study is to establish a sub-surface lithostratigraphic framework for the Middle Devonian interval using rigorously defined well log criteria integrated with X-ray diffraction, TOC, and petrophysical data. Secondly, this study advances the understanding of well log response in organic-rich shale units to derive important reservoir properties (e.g., organic-richness, gas content and lithology) using a combination of readily available well logs (gamma ray, neutron porosity, bulk density, photo electric, and resistivity curves) and the more modern spectral gamma ray logs. Using log data, a relationship was recognized between the uranium concentration, and increased gas content and organic richness. The incorporation of the spectral gamma ray logs and the traditional well logs available in the basin allowed for new methods of gas identification as well as the re-defining of water saturation calculations for the Middle Devonian interval that can be used to locally evaluate economic potential. Finally this study used the litho-stratigraphic framework and defined well log relationships to create a regional picture of the depositional dynamics for the Middle Devonian interval. Local depositional trends were observed in which deeper structures affected the local topography and created conditions that were more favorable for organic matter accumulation and preservation. Regionally, a trend striking north-west to south-east marked an area of increased organic preservation as well as distinct changes in unit thicknesses. This trend persists and affects depositional patterns for the entire interval, creating a shelf-break environment that was topographically higher to the east and north. The local and regional trends and their affect on the deposition of all of the stratigraphic units, allows for improved recognition of areas for economic gas production in the Middle Devonian of the central Appalachian basin.

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