Role of alternating redox conditions in the formation of organic-rich interval in the Middle Devonian Marcellus Shale, Appalachian Basin, USA

Abstract

Geochemical, isotopic and petrographic analyses were performed on a 30-m core of the Marcellus Shale obtained from Greene County, Pennsylvania, to understand the dominant controls on organic matter deposition in the black shale study units. Our study suggests that the regeneration of nutrients, such as nitrogen (N) and phosphorous (P), may have played a key role in the formation of organic carbon (OC)-rich intervals in the Marcellus Shale. The decomposition of organic matter is likely to have released N and P into the water column, and the episodic upward mixing of these nutrient-enriched waters enhanced primary production. The ratios of C org /N bulk and C org /P tot are significantly higher in the OC-rich zone of the core (i.e., defined as TOC > 4% and located between 2393 and 2406.5 m depth). The high C org /P tot and C org /N bulk ratios of the preserved organic matter may reflect the release of N and P by microbial processes, indicating the recycling of nutrients during deposition of the OC-rich interval. In addition, our data show a positive relationships between the C org /P tot and C org /N bulk ratios and the organic carbon content, which indicate that the recycled nutrients may have promoted primary

Characterization of Marcellus Shale and Huntersville Chert before and after exposure to hydraulic fracturing fluid via feature relocation using field-emission scanning electron microscopy

“…Rock core utilized during this experiment was retrieved in September 2008 from a well site located in Greene County, Pennsylvania [4]. The main core sample was stored under atmospheric conditions until 2014.…”

Comparison of Pore Fractal Characteristics Between Marine and Continental Shales

“…In the US, more than 70% of current shale gas production was extracted from marine shales in the Devonian-Mississippian period, mainly including Antrim shale, Ohio shale, New Albany shale, Marcellus shale, Barnett shale, Fayetteville shale and Woodford shale. [20][21][22] In China, the commercial breakthrough for shale gas extraction has hitherto been made only in marine shale but not yet in continental shale, even though there contains huge shale gas potential in continental shale. 23 Marine and continental shales were formed under disparate sedimentary conditions and therefore have some different properties.…”

Linking the Qinling Orogeny with the Chang 7 shale (Triassic Yanchang Formation) deposition: Evidence from major, trace, and rare earth element geochemistry

“…The diminished values were likely attributed to the relatively high sediment influx under the conditions of intensive chemical weathering. Beside high primary productivity and anoxic conditions, deposition of organic‐rich black shales can also be influenced by SR (e.g., Chen et al, ; Chen & Sharma, ; Lash & Blood, ; Sageman et al, ; Werne et al, ). Increasing fluxes of clastic sediment by fluvial, aeolian, and volcanic processes lower the concentration of organic carbon by dilution (Rimmer, Thompson, Goodnight, & Robl, ).…”

“…The recent boom in shale oil and gas production in the Ordos Basin has focused research attention on the Chang 7 organic‐rich shale of Upper Triassic Yanchang Formation. Organic‐rich shales are commonly defined as shales containing high total organic carbon (TOC) content, and most of them are characterized by high uranium concentrations and gamma‐ray values greater than 200 API units (e.g., Chen & Sharma, , ; Lüning & Kolonic, ; Qiu et al, ; Wang & Carr, ). The Upper Triassic Chang 7 lacustrine organic‐rich shale is considered to be an especially attractive hydrocarbon source rock, accounting for the bulk of Mesozoic oil and gas reservoirs in the Ordos Basin (Qiu et al, ).…”