Elemental Mapping and Characterization of Petroleum-Rich Rock Samples by Laser-Induced Breakdown Spectroscopy (LIBS)

Abstract

The application of Laser-Induced Breakdown Spectroscopy (LIBS) is presented for the direct elemental analysis of hydrocarbon-rich solids. In recent years, LIBS has become a powerful tool for obtaining elemental information and mapping analysis of different petroleum-rich samples with minimal to no sample preparation and without the need to separate the organic matter from the inorganic matter. By selecting the most intense and representative lines, the element distribution in a 2D map can be accessed in less than ten hours. For this reason, two types of hydrocarbon-rich solids were chosen for examination, i.e., core and shale. Nineteen elements were identified in the samples, and 2D mapping for Ca, Mg, Fe, Ti, Ni, C, H, K, O, and S is presented here. A detailed distribution of the elements, and the main components of the hydrocarbons present in these samples, were determined using LIBS. The H/C molar ratio was determined by building H and C calibration curves using data obtained from classical elemental analysis via combustion. These calibration curves contained a high degree of linearity (R2 > 0.98) with the limits of detection for C (193 nm), C (247 nm), and H (656 nm) of 848 mg kg−1, 353 mg kg−1, and 3.5 mg kg−1, respectively. By combining all of this information, LIBS allowed us to determine how these elements were spatially distributed, which elements were dominant in a given sample, and how much hydrocarbon was present, as well as providing a quantitative determination of the H/C molar ratio, and its correlation with the source of origin.