ELEMENTAL MAPPING OF SHALE ROCKS USING LASER INDUCED BREAKDOWN SPECTROSCOPY (LIBS)

Geochemical characterization of source rocks plays a key role in oil and gas exploration. While elemental composition of shale can provide clues to the rock properties affecting the oil and gas accumulation, mapping of rocks for elemental distribution can be useful to determine mineral phases and chemical zonation within a mineral. In this study, laser induced breakdown spectroscopy (LIBS) was used for the analysis and mapping of shale samples obtained from various locations in the United States. LIBS is a fast analytical technique that can provide elemental information of every element on the Periodic Table (including C, H, N, O) of a given sample. Additionally, LIBS provides depth profiling and can operate in extreme conditions, which makes it an attractive tool for in-situ analysis of the bore hole walls at various drilling depths. Shale samples were analyzed using a 266 nm Nd:YAG nanosecond pulse duration laser (J200 LIBS instrument) and a grid pattern that covered 64-144 mm² area. The data collected from these experiments were used to construct 2D elemental maps and determine elemental concentration for each sample. The accuracy of analysis was assessed by analyzing the samples of known elemental concentrations. This study shows how the spatial elemental (including C and H) composition varies as a function of the sample location and illustrates the benefits of LIBS over existing analytical techniques.