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Lithostratigraphy of Middle and Upper Devonian Organic-Rich Shales in West Virginia - Report of Investigation RI-35

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Abstract and Product Overview

Abstract
Middle and Upper Devonian organic-rich shale formations in West Virginia include significant oil and gas source rocks and reservoirs. Formal lithostratigraphy for these units is well established in the southern and eastern portions of the State but is typically less well-defined in the northern and central areas where the units occur deep in the subsurface and where resource development is currently concentrated. Historically, subsurface lithostratigraphic terminology has been assigned by reference to units defined in outcrops along basin margins and extended into the subsurface through correlation of geophysical well logs. However, lateral changes in the lithology of units complicate the extension of lithostratigraphic designations defined in outcrop over long distances. Further, terminology emanating from the more distal northern (western New York) and western (Ohio and Kentucky) basin margins is not readily reconciled with terminology established in more proximal outcrops along the Allegheny Front and extended westward. Differences in the nature of information available from outcrop studies as opposed to that provided by logs further complicate the reconciliation of terminology. As a result, the geographic distribution and lithostratigraphic nomenclature for many Middle and Upper Devonian shales remains unsettled, particularly in the basin center.
 
In this study, correlation of log data from approximately 400 wells throughout West Virginia enables detailed mapping of organic-rich facies and allows the determination of appropriate vertical and lateral lithostratigraphic unit boundaries throughout the subsurface of northern, central, and southern West Virginia. All nomenclatural recommendations presented are based on precedence and utility. This study focuses on the Middle Devonian Hamilton Group and its constituent Marcellus and Mahantango formations. Within the Marcellus, a lower Union Springs Member, a middle Cherry Valley Member, and an upper Oatka Creek Member are recognized within northeastern West Virginia only. Throughout the rest of the subsurface of the central, western, and southern parts of the State, the Marcellus has no distinguishable members, although three informal sub-units can be mapped with moderate confidence over much of the area. In the Upper Devonian, the occurrence and limits of the Harrell Shale (and its basal Burket Shale Member), and its westward lateral transition into the largely-correlative Genesee Formation (with basal Geneseo Shale and upper West River Shale members) are mapped. Maps also detail the position at which the Sonyea Formation (with basal Middlesex Shale and upper Cashaqua Shale members), West Falls Formation (with basal Rhinestreet Shale and upper Angola Shale members), Java Formation (undifferentiated), and lower part of the Huron Member of the Ohio Shale transition eastward into age-equivalent strata of the Brallier Formation.
 
Report
A peer-reviewed report detailing the study is available online as an Adobe .pdf. The work includes a description of data and methods and review of all lithostratigraphic units associated with organic-rich shales in the interval between the Marcellus Formation and the lower part of the Huron Member of the Ohio Shale. A series of maps shows the thickness of each unit and the location of lateral boundaries between age-equivalent units. The report includes 31 figures of which 19 are isochore maps.
 
Cross-Sections
Ten gamma-ray geophysical well log lithostratigraphic cross-sections, six west to east and four north to south, spanning much of West Virginia are available online as Adobe .pdf files. In keeping with the study, depending on the particular area of the State, the cross-sections include strata from the top of the Onondaga Limestone and equivalents (Hunterville Chert and Needmore Shale) to the top of the lower part of the Huron Member of the Ohio Shale. In addition, the Needmore Shale is included in a portion of the eastern part of the State. The datum for the sections is the base of the Union Springs Member of the Marcellus Formation. The location of possible faults are noted on the cross-sections. There is no horizontal scale implied. The cross-sections can be viewed online or printed. For online viewing, zoom in to read detail. For printing, each cross-section has been designed to fit on 11 x 17 inch (tabloid) paper in landscape mode.
 
Interactive Map
The interactive map application provides online access to all maps included in the report with the added convenience of being able to zoom in to read API number and thickness labels as well as to link to cross-sections and all WVGES non-study data about a particular well. WVGES interactive map "Tips and Tricks" are available from the map in the upper right-hand corner of the application.
 
Data Spreadsheet
A Microsoft Excel spreadsheet containing a record of all study stratigraphic unit depths (log measured as well as subsea depths) and interval thicknesses is available.
 
Page last revised May 24, 2018.
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