A recent NETL study demonstrated that laser-induced breakdown spectroscopy (LIBS) technology can provide a cost-effective, rapid and precise method for determining the elemental composition of organic-rich shales like the Marcellus Shale formation, the largest reservoir of natural gas in the Appalachian basin. This characterization work is paving the way for producers to begin rapidly targeting resources with greater accuracy.
LIBS is a versatile and rapidly advancing analytical technique that can detect concentrations of all known elements and requires minimal sample preparation. The technology works by creating a high-intensity pulse of light that is focused on a sample. This produces a spark of light in all directions, made up of atomic emissions from the different elements found in the sample. This light is then analyzed by a spectrometer for elemental composition.
Knowing what elements are present in shale formations can help determine mineral composition as well as how porous the rock may be and how easily a fluid could travel through the formation — critical properties that affect how natural gas producers approach drilling operations. Additionally, the characterizations made by NETL’s LIBS systems can provide information on the concentrations of carbon and hydrogen, pinpointing areas of higher organic material concentration that may indicate high gas production potential.
In the study, NETL researchers used a LIBS system to determine what elements were present in a variety of samples procured from the Marcellus Shale Energy and Environment Laboratory (MSEEL) in Morgantown, West Virginia. Information collected in the study was then used to construct 2D maps illustrating which elements were present in the shale samples. The accuracy of the NETL analysis was confirmed by analyzing a shale sample of known elemental concentrations and obtaining a good agreement between analyzed and reference values.
This study has demonstrated that LIBS can be used to determine elemental composition variations in hydrocarbon-bearing shales in a laboratory setting, but this type of analysis can also be accomplished without ever removing a sample from the subsurface environment. A field-deployable LIBS sensor could be used downhole to achieve the same kinds of results in situ. This method would have several advantages over the current techniques, including X-ray fluorescence and scanning electron microscopy-energy dispersive spectroscopy, as the LIBS system can provide the same accurate results for all required elements including carbon and hydrogen without the added time, increased cost and careful sample preparation.
As worldwide natural gas demand continues to increase, producing shale gas quickly and economically will play a major role in maintaining American energy dominance. NETL’s development of cutting-edge LIBS technology is one way the Lab is working to find solutions to today’s energy challenges and helping to explore the full potential of the nation’s fossil energy resources.