A MULTI-PROXY ANALYSIS OF THE MARCELLUS SHALE IN NORTHEASTERN PENNSYLVANIA

Varying exploration success in the Marcellus shale has revealed the formation as widely heterogeneous over relatively short distances. Integration of geochemical and geophysical parameters by way of analysis of multiple proxies can reduce risk by increasing the knowledge of the formation at specific locations. The goal of this project is to independently evaluate parameters such as TOC and depositional environment reconstruction by way of both geophysical and geochemical data for two wells in Northeastern Pennsylvania. Cuttings from Well 1 were collected every 10 feet over the entire 370 feet Marcellus section for a total of 37 samples. Twenty core chips that represent 80 feet from the lower and upper sections of the Marcellus were collected from Well 2. These samples were powdered in a mini-ball shaker device and prepared for analysis using a Rock Eval 6™ pyrolysis instrument and a Thermo-Fisher Niton™ hand-held X-ray Fluorescence (XRF) instrument in the School of Geosciences at the University of Louisiana at Lafayette. The XRF instrument was calibrated using three standard reference shales available from the US Geological Survey. These standards were additionally run intermittently to evaluate uncertainty. Direct TOC measurements from Rock-Eval pyrolysis (up to 4% TOC in Well 1 and 10% TOC in Well 2) are compared with several potential elemental proxies such as S, Fe, V, and Mo accumulations. TOC was additionally compared with geophysically-based TOC estimations using gamma ray (GR) values and the porosity-resistivity overlay technique. Depositional environments are reconstructed using major element data Si, Al, Ti, K and this was compared against reconstructions using GR, spontaneous potential (SP), and photoelectric (Pe) values. We found that geophysical well logs from the two wells were virtually identical in GR, SP, Pe, resistivity, bulk density and neutron porosity. In contrast, the geochemical data paint a very different picture between the two locations demonstrating vastly different TOC values, and different redox conditions at the time of deposition. This reveals the challenges of using only well log geophysical data for evaluation of heterogeneous source rock plays. This investigation highlights the importance of using geochemical data for exploration in these complex environments.