--> Understanding kerogen composition and structure in pristine shale cores collected from Marcellus Shale Energy and Environment Laboratory

AAPG Eastern Section Meeting

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Understanding kerogen composition and structure in pristine shale cores collected from Marcellus Shale Energy and Environment Laboratory

Abstract

Organic-rich black shales have become a vital component of the US energy portfolio. Kerogen is the high molecular weight organic matter (OM) that serves as starting material for the oil and gas in these shales. Despite its importance, kerogen still remains one of the least studied components because traditional methods used to study it have limited applicability, especially in mature shale reservoirs. It has been noted that shales with a similar amount and type of kerogen and similar reservoir parameters, such as maturation, have different biomarker distribution, carbon (organic) isotopic signature, and produce different amount of hydrocarbons. These heterogeneities highlight the need to better understand the variability in composition and structure of kerogen to identify sweet spots for hydrocarbon production. This study utilizes sidewall cores collected from the experimental well at Marcellus Shale Energy and Environment Laboratory (MSEEL) in Morgantown, West Virginia. Samples were collected from different organic-rich zones in Marcellus Shale, and from its contact with the underlying Onondaga and overlying Mahantango formations. Samples were grounded to a particle size less than 500 µm and homogenized. Kerogen was extracted from grounded samples by removing soluble OM and mineral matrix using chemical and physical separation. Soluble OM, carbonate minerals, and silicate minerals were dissolved using di chloromethane (DCM), hydrochloric acid (HCl), and hydrofluoric acid (HF) respectively. Heavy minerals and pyrite were separated using zinc bromide (ZnBr2) solution. Different functional groups such as C=O, CH2, CH3, C=C, C-O, OH, C-OH were identified using FTIR (Fourier Transformed Infrared) analysis and the molar percentage of different carbon bonds were quantified using XPS (X-ray Photoelectron Spectroscopic) analysis. The data on functional groups and carbon bonds will be used in conjunction with isotopic, geochemical, and mineralogical data to understand the effect depositional environment and redox conditions have on structure and composition of kerogen.