Characterization of Kerogen and Source Rock Maturation Using Solid-State NMR Spectroscopy

Abstract

Solid-state NMR methods common to the analysis of polymers and other rigid solids are utilized for the study of kerogen, bitumen, and the organic content in source rocks. The use of straightforward nondestructive techniques, primarily employing solid-state NMR, is shown to provide useful information about both individual samples and changes between samples that cover a range of thermal maturities of type II kerogen. In addition to aromatic fraction and chemical structure, one of the most striking changes to isolated kerogen with maturity is the distribution of pore sizes, studied with both 129Xe NMR and complementary nitrogen physisorption, that may help to understand the process of bitumen generation. Ultimately, direct in situ analysis of source rock samples that allow kerogen and bitumen to be distinguished is desirable, as it would eliminate the time and effort to isolate and prepare kerogen samples. By proper consideration and removal of the background, we find that a clear 13C NMR signal can be obtained from source rock with total organic carbon weight as low as 2%. Simple 1H NMR methods are shown to quickly provide a qualitative measurement of the bitumen in source rocks, while 13C cross-polarization is found to be an easy method to distinguish kerogen from bitumen.

129Xe NMR on Porous Materials: Basic Principles and Recent Applications

“…The use of solid‐state NMR was investigated by Clough et al as a non‐destructive technique to directly assess the organic matter inside the source rock. [ 133 ] The authors successfully determined the composition of several kerogen, bitumen and source rock samples with 1 H, 13 C direct excitation, and 13 C cross polarization solid‐state NMR under MAS. With 129 Xe NMR using the Fraissard approach, [ 24 ] the authors were able to correlate the decreasing size of mesopores with increasing thermal maturity of the samples, thus introducing 129 Xe NMR as a straightforward, non‐destructive tool.…”

Universal Curves Describing the Chemical and Physical Evolution of Type II Kerogen during Thermal Maturation

“…Direct characterization of carbon molecular species (molecular structures) in kerogen and other carbonaceous materials complements the analysis of bulk elemental abundances and is performed using solid-state spectroscopic techniques. These techniques include 13 C nuclear magnetic resonance (NMR), ,− infrared (IR), − ,,,,− Raman, ,, and X-ray photoelectron spectroscopy (XPS) . These approaches enable analysis of bulk, solid, unaltered OM, preserving molecular structural information that is otherwise lost using thermal decomposition techniques.…”

Evaluating Molecular Evolution of Kerogen by Raman Spectroscopy: Correlation with Optical Microscopy and Rock-Eval Pyrolysis

“…In the kerogen structure, aromatics that are linked by aliphatic and heteroatoms [15], in which solid bitumen can be trapped [61,62]. The increase in carbon aromaticity that takes place during maturation has been also detected during natural maturation that is caused by igneous intrusions [63][64][65][66][67][68], or by the increase in depth of burial [69][70][71].…”