Fig. 2 The correlation between the simulated temperature and measured vitrinite reflectance (Ro )
The changes in gaseous hydrocarbons, expelled oil, and residual bitumen with increasing Ro are shown in Fig. 3. With an increase inRo , the gaseous hydrocarbon yield tended to increase gradually. When Ro = 0.82–1.09%, the yield of gaseous hydrocarbons increased slowly with a smaller change in amplitude. When Ro = 1.65–2.56%, the yield of gaseous hydrocarbons increased rapidly at a constantly increasing rate, which had a larger increase in amplitude. When Ro = 2.56–3.24%, the yield of gaseous hydrocarbons increased sharply with an increase in amplitude = 124.74%.
Overall, the yield of expelled oil first reached a specific value and remained constant at the corresponding value. The yield of expelled oil at Ro = 0.82–1.09% and corresponding simulated temperature (Ts ) = 335–360 ℃ increased rapidly from 19.36 to 46.76 mg/g TOC, with an increased amplitude of 141.53%. When Ro = 0.82–1.09% (Ts = 335–360 ℃), the high amplitude of expelled oil increased slowly from 46.76 to 50.16 mg/g TOC compared with the previous thermal evolution stage. At the stage where Ro > 1.65%, i.e., after the simulated temperature was higher than 400 ℃, the yield of expelled oil was 50.16, 50.07, 50.25, 50.18, and 50.22 mg/g TOC, respectively. Therefore, the yield of the expelled oil was constant.
For residual bitumen, i.e., the yield of residual oil, a continuously decreasing tendency was observed. When Ro = 0.82–1.09% (Ts = 335–360 °C, the medium maturity stage), the residual bitumen decreased from 17.78 to 17.01 mg/g TOC with increasingRo ; however, the change was not apparent. When Ro = 1.09–1.65%, the residual bitumen suddenly decreased from 17.01 to 5.7 mg/g TOC with a decreased amplitude of 66.49%. When Ro = 1.65–2.3%, a continuously declining trend slowly occurred in the yield of residual bitumen, with values of 5.70, 3.41, and 3.55 mg/g TOC. Thereafter, when Ro > 2.56%, the residual bitumen decreased from 1.35 to 0.47 mg/g TOC, close to 0.