NOBLE GAS GEOCHEMISTRY OF THE MARCELLUS SHALE FORMATION: A PROSPECTING TOOL FOR HYDROCARBON GAS MIGRATION

Recent improvements in horizontal drilling and hydraulic fracturing technologies have opened numerous unconventional reservoirs such as black shales for hydrocarbon exploration and production globally. The Marcellus Formation in the northern Appalachian is an archetypal example of an unconventional energy basin. To better characterize the porosity, permeability, thermal maturity, and geological fluid flow within the Marcellus Shale, I analyzed the helium, neon, and argon isotopes and uranium, thorium, and potassium concentrations of rock cuttings from a series of intervals along the lateral of a well in the Marcellus Shale. By comparing the anticipated radiogenic production of ⁴He, ²¹Ne, and ⁴⁰Ar based on measured U and Th concentrations to measured values, I can evaluate the history of natural gas migration within the Marcellus. Specifically, I focus on how the ⁴He/²¹Ne ratio compares to anticipated production rate and how it changes throughout the lateral of the well. These measurements allow me to determine how porosity and permeability vary along the well and to determine sweet spots of gas accumulation. Areas with ⁴He/²¹Ne at or above production ratios predict gas-in-place “sweet spots”, while intervals with ⁴He/²¹Ne below anticipated production reflect dead zones that have lost gas over time.