Determining the Type, Amount and Kinetics of Hydrocarbons Generated in a Marcellus Shale Maturity Series
In the past decade, shale oil/gas boom transformed the economics of the United States energy sector. As of December 2018, shale gas contributes to 70% and tight oil contributes to 60% of total U.S. dry gas and crude oil production respectively. Despite this dramatic increase in hydrocarbon (HC) production, the mechanism and kinetics of HC generation in shale reservoirs are not well understood. In addition, errors in gas/oil in place calculations result in inaccurate estimation of HC reserves. One of the primary ways to overcome these challenges is to track the compositional evolution of kerogen cracking products on a bulk to molecular level as a function of maturity. In this study, we determined the amount, composition, and timing of hydrocarbon generation using a combination of Pyrolysis-Gas Chromatography (Py-GC) and Micro Scale Sealed Vessel (MSSV) Py-GC pyrolysis experiments in a Marcellus shale maturity series. Our results indicate that the pyrolysates on maturation generally become more gas rich and aromatic, and the inferred petroleum type evolves from Paraffinic-Aromatic-Naphthenic (P-N-A) low wax to gas condensate at VRo > 1. Using MSSV-Py-GC, we evaluated the “late gas” generation potential by determining the gas yields at higher temperatures (560 oC and 700 0C). Following the approach of Mahlstedt and Horsfield (2012) our results show that late gas ratio (LGR) for the least mature Marcellus shale kerogen sample is greater than 0.6 indicating a high late gas potential. Further, it was determined that late gas potential increases with maturity up to 2.0% VRo to roughly 40 mg/g TOC and then decreases again during metagenesis due to late methane generation. Since the traditional source rock evaluation is based on open-system pyrolysis screening-methods (which does not incorporate the late gas potential), our results demonstrate that the previous estimations on Marcellus shale reserves can be underestimated.
AAPG Datapages/Search and Discovery Article #90373 © 2019 AAPG Eastern Section Meeting, Energy from the Heartland, Columbus, Ohio, October 12-16, 2019