Rapid Analysis of Kerogen Hydrogen-to-Carbon Ratios in Shale and Mudrocks by Laser-Induced Breakdown Spectroscopy

Abstract

Evaluation of organic matter quality in petroleum source and reservoir rocks is vital for economic, drilling, and production decisions. However, current methods for assessing kerogen quality in shales and mudrocks are either time-intensive and undesirable from a health, safety, and waste-disposal standpoint or indirect measurements of the factors of greatest interest and utility (e.g., kerogen hydrogen content). We present a new approach using laser-induced breakdown spectroscopy (LIBS) to both directly and quickly measure kerogen hydrogen-to-carbon elemental ratios in shales and mudrocks, providing a rapid means of assessing kerogen quality and thermal maturity with minimal sample processing. Elemental spectral intensities, including hydrogen and carbon, were monitored during LIBS measurements by optical emission spectroscopy, following ablation of a small portion of rock. Changes in the elemental intensities in the spectra over the course of LIBS measurements were then related to H/C ratios determined on isolated kerogens from the rock samples using multivariate analysis. Predicted kerogen H/C ratios from the LIBS measurements of whole rock samples were well-correlated (R 2 = 0.99) to values determined for kerogen isolates measured by elemental analysis. These results demonstrate that LIBS is a promising method for examining kerogen quality and thermal maturity in source and reservoir rocks. Because LIBS does not require samples to be pulverized and can be conducted on sub-millimeter scales, this approach will also allow for highly localized, spatially resolved measurements on heterogeneous geologic samples.

Determination of Heating Value of Estonian Oil Shale by Laser-Induced Breakdown Spectroscopy

“…Directing a number of laser shots with high repetition rate to the same spot of the sample under an argon purge, the changes in the spectral line intensities in LIBS spectra over the course of measurements were related to H/C ratios determined on isolated kerogens from the rock samples. Predicted kerogen H/C ratios from the LIBS measurements of whole rock samples were well correlated (R 2 = 0 99) to values determined for kerogen isolates measured by elemental analysis [6]. An important advantage of the method is that the decay of intensities of H and C lines with the growth of laser shot number allowed a clear separation of H and C in the organic part of oil shale from that in the inorganic part.…”

“…In [6,7], laser-induced pyrolysis was used for determination of oil shale characteristics. Directing a number of laser shots with high repetition rate to the same spot of the sample under an argon purge, the changes in the spectral line intensities in LIBS spectra over the course of measurements were related to H/C ratios determined on isolated kerogens from the rock samples.…”

Accurate determination of structural H2O in rocks using LIBS coupled with machine learning algorithms extensively exploring the characteristics of the Hα line

“…In petroleum exploration, the determination of hydrogen using LIBS offers the potential of direct detection of bitumen in a drill core during a drilling project. 2 Other applications are focused on hydrogen determination in oil shales and associated rocks (limestone or mudrock), 16,17 as well as in gas producing shales. 18 Such determination is also important for the investigation of the past evolution of Mars.…”

Rapid Determination of Bitumen Content in Athabasca Oil Sands by Laser-Induced Breakdown Spectroscopy

“…In addition to the ability to measure simultaneously several atomic elements, LIBS can measure light elements ( Z < 12) such as carbon, hydrogen, oxygen, etc., unlike XRF. Studies on shale , and coal , demonstrate that LIBS may be used to measure the organic components of natural samples. Moreover, the development of spectral analysis tools such as chemometrics − makes the LIBS spectroscopy a more powerful tool for quantitative measurements. , All of these features make LIBS an excellent candidate to characterize the oil sands composition.…”