Portable Raman spectroscopic analysis of bulk crushed rock

This study presents a simplified method and empirical relationships for determining organic matter thermal maturity using a portable Raman system equipped with a 785 nm laser, for analysis of crushed, whole-rock samples. Several sets of rocks comprised of shale and coal samples with various mineralogical composition, thermal maturity, total organic carbon (TOC), and age were used to test the method and build correlations between Raman band separation (RBS) values and traditional thermal maturity indicators; organic matter reflectance (Ro) and programmed temperature pyrolysis (Tmax) values. Several sample preparation methods were tested on cuttings material and standard deviation values for RBS were minimized by washing, drying, and hand crushing the material to pass through a 40-mesh sieve, although less preparation can still yield reliable results. For the coal data set, Ro values range from 1.21-4.08% and correlated RBS values plateau at ~250 cm-1 above Ro=3.0% suggesting its correlative application below this maturity level. The second data set, comprised of disparate shale samples where both vitrinite and solid bitumen reflectance values were reported, have Ro values that range from 0.40-4.62%. Above 3.35% Ro, the corresponding RBS values plateau at ~290 cm-1, thus correlations were evaluated with a linear equation (R2= 0.96) between 0.40-3.35% Ro. Shale samples with Ro