(644g) Laser Induced Breakdown Spectroscopy (LIBS): A Potential Technique for in-Situ Geochemical Characterization of Unconventional Shales

Shale gas is an important asset in the United States and therefore, understanding the geochemical composition of shale formations is of utmost interest and importance. Knowledge of mineralogy and overall chemical constituency can inform engineering and production decisions in the reservoirs and are important factors that influence decisions about drilling locations. The gas capacity can be correlated based on the organic and inorganic content of the shale. Currently, rock core must be retrieved from depth and analyzed using X-ray fluorescence (XRF) or other analytical techniques outside of the wellbore. While these techniques provide excellent data, most of them do not measure all the required elements simultaneously and the analyses are limited to the ambient conditions at the surface. In this study, laser induced breakdown spectroscopy (LIBS) was used as an alternative technique for the analysis of tight shale. LIBS is a fast analytical technique that can provide elemental information of every element on the Periodic Table (including C, H, N, O) both at surface and in-depth of a given sample. Additionally, LIBS can operate in extreme conditions which makes it an attractive tool for in-situ analysis of the core at various drilling depths. Shale samples taken from a Marcellus shale well at depths ranging from 7498-7551 feet were analyzed using a 266 nm Nd:YAG nanosecond laser (LIBS instrument) and an 81 x 81 grid pattern that covered an 8 x 8 mm area. The data collected from these experiments were used to construct 2D elemental maps for each sample. This study shows how the spatial elemental (including C and H) composition varies as a function of the sample depth and illustrates the benefits of LIBS over existing analytical techniques.