Model representations of kerogen structures: An insight from density functional theory calculations and spectroscopic measurements

Abstract

Molecular structures of kerogen control hydrocarbon production in unconventional reservoirs. Significant progress has been made in developing model representations of various kerogen structures. These models have been widely used for the prediction of gas adsorption and migration in shale matrix. However, using density functional perturbation theory (DFPT) calculations and vibrational spectroscopic measurements, we here show that a large gap may still remain between the existing model representations and actual kerogen structures, therefore calling for new model development. Using DFPT, we calculated Fourier transform infrared (FTIR) spectra for six most widely used kerogen structure models. The computed spectra were then systematically compared to the FTIR absorption spectra collected for kerogen samples isolated from Mancos, Woodford and Marcellus formations representing a wide range of kerogen origin and maturation conditions. Limited agreement between the model predictions and the measurements highlights that the existing kerogen models may still miss some key features in structural representation. A combination of DFPT calculations with spectroscopic measurements may provide a useful diagnostic tool for assessing the adequacy of a proposed structural model as well as for future model development. This approach may eventually help develop comprehensive infrared (IR)-fingerprints for tracing kerogen evolution.

How Do Subduction Zones Regulate the Carbon Cycle?

“…First-principles approaches are now shedding light on the microscopic pathways involved in this process. 46,47 Because the transformations modeled by (10.1) are so slow in nature, it is even conceivable that the coldest slabs (e.g. the Mariana and the Aegean OC subduction hot spots) could reach the diamond stability field before completion of the carbonization and graphitization process.…”

Oxidative Kerogen Degradation: A Potential Approach to Hydraulic Fracturing in Unconventionals

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Evaluation of Spatial Alignment of Kerogen in Shale Using High-Resolution Transmission Electron Microscopy, Raman Spectroscopy, and Fourier Transform Infrared

“…Shale gas is known as an important unconventional gas resource in the USA, China, and some other countries. − In shale, organic matter (OM) has been proven as the major storage house for shale gas. , On one hand, free gas is mainly stored in nanoscale organic pores and these nanoscale organic pores contribute to the largest part of the total pore volume . On the other hand, organic matter is also considered as the most important absorbent for adsorbed gas storage. , In recent years, it has been recognized that the molecular structure of organic matter has great significance in further understanding gas storage and transport. − Some micropores (<2 nm) are formed within the three-dimensional (3D) molecular structure, and it is feasible to utilize the 3D molecular structure to study pore size distribution, pore morphology, and fractal features of these pores. ,, …”