SEDIMENT PROVENANCE STUDY OF THE MARCELLUS SHALE: AN ANALYSIS BETWEEN THE ORGANIC-RICH FACIES AND THEIR DEPOSITIONAL HISTORIES

Currently, no geological model exists to explain the variability and distribution of organic-rich facies in the Marcellus Shale (MS). Within the central Appalachian basin, there are two “sweet spots”, one in NE Pennsylvania and another in SW Pennsylvania (PA)/North-Central West Virginia (WV). In these areas, the MS has an average TOC of 5-18 wt% and is highly productive for natural gas. In contrast, outside these areas, the MS has lower TOC and therefore lower production.

One possible explanation for the low TOC in regions of the MS is that thermal maturation has led to degradation of kerogen-hosted pores or over-maturation of organic matter to deplete the resource. This hypothesis is being tested by comparing the thermal maturity of the MS in the lower productivity areas using Raman spectroscopy. Raman spectroscopy is an efficient and inexpensive technique when compared to vitrinite reflectance (VR_o). Raman spectra from the carbon bonds of organic matter show a D-band (disordered band) and a G-band (graphic). With increasing thermal maturation the D-band is located at a lower frequency (cm^-1). Also, the G-band’s full width half maximum values and frequency (cm^-1) decrease with increasing thermal maturation.

Raman spectra were acquired from core chips, at depths where VR_o was measured, from Taylor County, WV (average TOC of 4 wt%) and Clearfield County, PA (average TOC of 4 wt%). The Taylor Co. VR_o averaged around 1.4% and the Clearfield Co. VR_o averaged around 2.7%. Raman Spectral acquisition parameters were: a 473 nm laser, ND filter of 1%, 600 grooves/mm, a pinhole size of 200 μm, and an acquisition time of 5 seconds. Raman spectra from these lower TOC regions were compared to the higher TOC (average TOC of 6 wt%) MS of the MSEEL (Marcellus Shale Energy and Environmental Laboratory) well in north-central WV, where VR_o was not observed. The MSEEL well is speculated to have a lower thermal maturity than the Taylor Co. and Clearfield Co. wells, making it within the ideal thermal maturity range. Analysis revealed that the D and G-band frequencies for the MSEEL well are lower relative to the lower TOC wells.

Future work will compare provenance record of the MSEEL well with the wells located in Taylor Co. and in Clearfield Co. using Sm-Nd isotopic analysis to compare influence of sediment provenance on the TOC of these wells.