INFERRING BIOGEOCHEMICAL INTERACTIONS IN DEEP SHALE RESERVOIRS AT THE MARCELLUS SHALE ENERGY AND ENVIRONMENT LABORATORY (MSEEL)

This study seeks to use isotopic and geochemical proxies to understand water-rock-microbe interactions taking place in shale gas formations during and after drilling and hydraulic fracturing. Due to isotopic fractionations associated with biological and geochemical processes that take place after injection of hydraulic fracturing fluids into the reservoir, isotopes of carbon (¹³C), hydrogen (D), oxygen (¹⁸O) and sulfur (³⁴S) act as good water-rock-microbe interaction “tracers”. Determination of their ratios alongside temporal changes to the geochemistry allows us to observe nutrient cycling and geochemical reactions taking place.

The Marcellus Shale Energy and Environment Laboratory (MSEEL) site in Monongalia County, West Virginia has provided access to water and gas samples from all stages of drilling and production in a Marcellus shale natural gas well to infer these water-rock-microbial interactions. The MIP#3H and #5H wells near Morgantown were hydraulically fractured in December 2015. All fluids injected and returned from the wellbores, as well as produced gas, were analyzed for isotopic (WVU Stable Isotope Laboratory) and geochemical signatures (DOE-NETL and OSU).

The carbon isotopic signature of dissolved inorganic carbon (δ¹³C_DIC) in the injected freshwater and fracturing slurry has values of -8.7‰ and -8.2‰ V-PDB respectively. However, ¹³C_DIC of produced water from these wells ranged from +10‰ to +31‰ V-PDB. High resolution sampling reveals a sharp initial enrichment of ¹³C_DIC during the initial three day flowback period, followed by a continued enrichment over time as sampling progressed. Carbonate mineral veins in the hydraulically fractured zone are being analyzed as a potential source for this enrichment, although microbial activity during fracturing may also play a role. ¹³C/D-methane will be analyzed to determine microbial interactions. In addition, genomic data will be provided by collaborators at OSU to identify changes in microbial taxa within the formation.