Title

Sequence Stratigraphy, Distribution and Preservation of Organic Carbon, and Reservoir Properties of the Middle Devonian Marcellus Shale, of the Central Appalachian Basin; Northern West Virginia and Southwestern Pennsylvania

Semester

Fall

Date of Graduation

2011

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Geology and Geography

Committee Chair

Timothy Carr.

Abstract

The Middle Devonian Marcellus Shale of the central Appalachian basin is an unconventional resource play with approximate aerial extent of 34,000,000 acres (137,000 km²), and an estimated 84 trillion cubic feet (2.4 trillion m³) of recoverable natural gas and three billion barrels of recoverable natural gas liquids. Advances in drilling and completion technology have enabled economic production of hydrocarbons from the Marcellus. Despite increased exploration and production of the formation, uncertainties remain regarding controls on spatial and stratigraphic variations in reservoir properties such as total organic carbon (TOC), mineralogic composition, and authigenic components. Additionally, there is a lack of understanding of depositional environments in terms of stratification of the water column, paleo-redox states, and sedimentation rates. Integration of core data, including sedimentologic, lithologic, paleontologic, and geochemical properties, and associated geophysical logs into a sequence stratigraphic context assists in interpretation of depositional controls, and can contribute to a predictive reservoir assessment in areas with limited data control.;A transgressive -- regressive (T-R) sequence stratigraphic study of the Marcellus Shale interval, using 250 geophysical logs and four cored sections in northern West Virginia and southwestern Pennsylvania, indicates that the Union Springs and Oatka Creek members of the Marcellus Formation and the Levanna Member of the Skaneateles Formation define three third-order stratigraphic sequences (i.e., MSS1, MSS2, SKS). The MSS1 stratigraphic sequence encompasses the Union Springs Member of the Marcellus Formation and extends from a gamma-ray inflection point and/or bulk density base line shift located near the top of the Onondaga Formation to either an erosional surface at the base of the Cherry Valley Member of the Marcellus Formation, or a gamma-ray minimum and/or bulk density maximum within the Cherry Valley Member (or stratigraphic equivalent). The MSS2 stratigraphic sequence encompasses the Oatka Creek Member of the Marcellus Formation and extends from the upper boundary of the MSS1 stratigraphic sequence to either an erosional surface at the base of the Stafford Member of the Skaneateles Formation, or a gamma-ray minimum and/or bulk density maximum within the Stafford Member (or stratigraphic equivalent). The SKS stratigraphic sequence encompasses the Levanna Member of the Skaneateles Formation and extends from the upper boundary of the MSS2 stratigraphic sequence to a gamma-ray minimum and/or bulk density maximum within a limestone or calcareous grey shale interval overlying the Levanna Member.;Physical core descriptions and geochemical data (i.e. TOC, x-ray diffraction, and x-ray fluorescence spectroscopy) provide support for the placement of stratigraphic surfaces and aid in interpretation of depositional conditions. Specific geochemical proxies for terrigenous sedimentation include the concentrations of calcium, aluminum, zirconium and silica; the ratio of titanium to aluminum and silica to aluminum; and total clay volume. Geochemical proxies for paleo-redox states include the concentrations of manganese, molybdenum, and barium; the ratios of molybdenum to aluminum, barium to aluminum, and thorium to uranium; the degree of pyritization (DOP); and the depletion of sulfur isotope 34S relative to 32S (delta34S).;Interpretation of depositional conditions of the study interval, utilizing integrated geophysical logs, core descriptions and geochemical data, suggests a dynamic environment characterized by varying relative sea-level, oxygen concentration, and sedimentation rates. Organic-rich shale units within the study interval were deposited under anoxic or possibly euxinic conditions initiated by relative sea-level rise. A significant portion of the silica within black shale intervals is biogenic and/or eolian sourced. Limestone beds and calcareous grey shale intervals were deposited under dysoxic/oxic conditions initiated by relative sea-level fall. Terrigenous input increases moving upward stratigraphically from the MSS1 through the SKS stratigraphic sequences and into overlying grey shale intervals. During periods of relative sea-level fall, carbonate production outpaced terrigenous sedimentation, resulting in deposition of concentrated skeletal beds. Gravity driven sediment flows and winnowing processes commonly introduced oxygenated waters to the basin resulting in diagenetic fronts and concentration of heavier mineral grains (titanium).;Variations in the thickness of the MSS1, MSS2, and SKS stratigraphic sequences are controlled by sediment input originating near the structural front east of the basin, and the paleo-topography of underlying strata. The MSS2 and SKS sequences display infilling of paleo-topographic lows in the underlying sequences, suggesting increased deposition by sediment driven gravity flows. Areas of rapidly increasing thickness of the MSS1, MSS2, and SKS stratigraphic sequences in the eastern portion of the study area are associated with the distal portions of fluvial sediment sources located on the basin margins.

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