Comparative Analysis of Maturity between Solid Bitumen and Bitumen Inclusions in Marine Shale of the Sichuan Basin and Its Geological Significance

HIGHLIGHTS (1) The organic matter maturity of the samples was calculated using the peak height ratio parameter and the peak spacing parameter from the laser Raman spectra of shale solid bitumen and bitumen inclusions, respectively. The results for shale solid bitumen were 3.32%–3.64% and 3.10%–3.38%, while the results for bitumen inclusions were 3.51%–3.71% and 2.75%–3.50%. (2) For the same sample, the data points of the calculation results based on the peak height ratio parameter were more concentrated, with a standard deviation coefficient range of 0.31–5.61, which was significantly lower than the 0.75–9.24 for the peak spacing parameter. This indicates that the peak height ratio parameter offers better stability. (3) For the same sample, the maturity of bitumen inclusions was generally higher than that of solid bitumen, the absolute difference ranged from 0.02% to 0.22%, with an average relative difference of 3.13%. This suggests that differences may exist in the thermal evolution processes between bitumen inclusions and shale solid bitumen.