Application of Laser Raman Spectroscopy to the Evaluation of the High-and Overhigh-maturity of Shale and Coal

Abstract

The parameters of Laser Raman Spectra can reflect the maturity of organic matter, but there are few related studies on the organic matter in high-and overhigh-maturity of shale and coal. The maturity of shale from Southern China and anthracite from the Qinshui and Bide-Santang Basin have been determined by Laser Raman Spectroscopy, rock eval pyrolysis and vitrinite reflectance for maturity analysis and are reported in this paper. The reflectance equation proposed previously, was applied and the reflectance gained by Raman (RmcRo) was calculated. The correlation fitted regressed with the pyrolysis peak temperature (Tmax) and measured vitrinite reflectance (Ro). The results show that the wedge-shaped bands/peaks, first order bands/peaks (D and G) and second order bands/peaks (S2, S3 and S4) of shale and anthracite spectra are clear. The Raman reflectance (RmcRo) shows good correlations with pyrolysis peak temperature (Tmax, R2=0.9173) and vitrinite reflectance (Ro, R2=0.9614). The Raman reflectance (RmcRo) shows consistency and reliability with Tmax and Ro in the maturity evaluation. The multi-point test of Raman can reveal the heterogeneous variation of shale during diagenesis and has more accuracy and higher reliability in heterogeneity reflecting than the previously carried-out single-point test. The shale has a larger variation coefficient of RmcRo than that of coal and shows stronger organic matter heterogeneity. The organic matter of shale shows heterogeneous variation during diagenesis, causing a larger variation coefficient of RmcRo than that of coal and stronger organic matter heterogeneity than those of coal. The research results provide a basis for the evaluation of the organic matter maturity of the high-over mature shale and coal.

Keywords

• maturity evaluation
• organic matter in shale and coal
• laser raman spectroscopy
• heterogeneity
• high-and overhigh-maturity