Varying exploration success in the Marcellus shale has revealed the formation as widely heterogeneous (e.g., limited sweet spots) over relatively short distances. Analysis of petrophysical well logs and rock mechanical properties cannot identify subtle differences in paleoenvironmental conditions that lead to these heterogeneities, resulting in the integration of inorganic geochemical data becoming more prominent. Several studies have established the effectiveness of inorganic proxies to gain insight into paleodepositional environments (e.g., redox, productivity, and siliciclastic influx) at the time of deposition. The goal of this investigation was to apply geochemical (Rock-Eval™ pyrolysis and X-Ray Fluorescence (XRF)) data from two wells located in Lycoming and Subsequenha counties of Pennsylvania to reconstruct the regional depositional conditions to identify the controls on production and preservation of organic matter (OM). Specifically, C–S–Fe relationships, Mo, V, and U were analyzed to reconstruct paleoredox conditions during deposition; P, Cu, and Zn were used as a proxy for paleoproductivity; and variations in siliciclastic input were evaluated using the ratios of Ti, Si, and K relative to Al.
Variations in the degree of pyritization (DOP) identified through C–S–Fe relationships, as well as variations in the enrichments of the redox-sensitive trace metals, suggest dysoxic and anoxic conditions at the locations of Wells 1 and Well 2, respectively. Analysis of the productivity proxies suggested that the accumulation of P, Cu, and Zn within the samples were dependent on redox conditions. While the higher accumulations and higher ratios of these elements to TOC in Well 2 could be indicative of more biological productivity at that location, it is more probable that it is a result of more anoxic conditions being present during deposition. Higher ratios of Ti to Al suggest Well 1 was in closer proximity to the paleobasin’s edge, explaining why more oxygenated waters were present at that location. Strong relationships between the studied proxies and TOC, along with consistencies between the disparate proxies, highlight the importance of using geochemical data for exploration in these complex environments.
|Commitee:||Gottardi, Raphael, Schubert, Brian|
|School:||University of Louisiana at Lafayette|
|School Location:||United States -- Louisiana|
|Source:||MAI 56/05M(E), Masters Abstracts International|
|Subjects:||Petroleum Geology, Geochemistry|
|Keywords:||Productivity, Redox, Siliciclastic, TOC|
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