Rapid geochemical and mineralogical characterization of shale by laser-induced breakdown spectroscopy

Detailed evaluation of shale geochemistry and mineralogy is important to assess petroleum reservoir quality, predict production potential and decide lateral placement and completion methods. Standard techniques for organic geochemical and mineralogical characterization are time consuming, can involve significant sample preparation and are prone to error. A new application for assessing shale samples is presented here: laser-induced breakdown spectroscopy (LIBS). A laser is used to rapidly pyrolyze shales and the changes in sample elemental composition during pyrolysis are monitored through optical emission spectroscopy. Unlike other common shale characterization methods, no specific sample preparation is required. Multivariate analysis is applied to the LIBS spectra to predict both organic geochemistry and mineralogy. The results show good correlation to TOC, Rock-Eval parameters and eleven minerals, including clay speciation. The technique also has the potential to directly measure organic hydrogen and oxygen and could provide an alternative to the indirect methods currently used.