Meso- and Macro-Scale Facies and Chemostratigraphic Analysis of Middle Devonian Marcellus Shale in Northern West Virginia, USA

摘要

The Marcellus Shale Energy and Environmental Laboratory (MSEEL), consists of four producing horizontal wells, two vertical pilot wells and a vertical microseismic observation well. To gain a detailed understanding of the Middle Devonian Marcellus Shale and surrounding shale and limestone intervals, I focused on the two vertical pilot wells (MIP-3H and MIP-4H). Understanding the vertical and lateral distribution of the shale lithofacies and changes in chemostratigraphy are critical to understanding the impact of depositional and diagenetic environments on hydrocarbon generation and production in shale gas reservoirs. Integrated geological and petrophysical characterization of the Marcellus and adjacent Onondaga Limestone through Mahantango Formation used available core and well log data.;Macro-scale lithofacies were determined through a combination of core and CT-scan descriptions. Meso-scale shale lithofacies, based on mineralogy and total organic content (TOC), used a combination of triple combo and advanced logging tools, which were calibrated to core data (XRD and source-rock pyrolysis). Chemostratigraphic analysis utilized x-ray fluorescence (XRF) to determine the major and trace element trends associated within the Devonian Marcellus-Mahantango interval. Integration of these three approaches were used to develop a depositional model.;The Devonian Marcellus-Mahantango interval is composed of six shale lithofacies both at the meso- and macro-scale. Petrophysical analysis shows that three well developed organic mudstone facies are present in the Marcellus interval. Chemostratigraphic (trace element concentrations) and petrophysical data (spectral gamma derived uranium content) indicate the highly organic-rich mudstone (TOC > 6.5 weight percent) facies in the lowest part of the Marcellus Shale compared to overlying units was deposited in a highly anoxic environment with decreased detrital influence indicated by silicon, aluminum, and titanium trends. The anoxic conditions and decreased detrital input allowed for preservation of organic matter in the lowest part of the Marcellus Shale.