Features of liquid hydrocarbon and biomarker maturity ratios during HTHP semi-open system pyrolysis of type II and III source rocks

In order to study the liquid hydrocarbon generated by laboratory pyrolysis and the biomarker maturity ratios in expelled oil with the increasing simulation temperature, the Hydrous semi-open system high temperature high pressure (HTHP) pyrolysis experiments was performed on Type II and III source rocks from 350 degrees C to 540 degrees C. The results showed that expelled oil yields in both samples have a trend of increased first and then decreased with the increasing temperature, while an opposite tendency occurred in the residual oil. The biomarker maturity ratios, such as Sigma C21-/Sigma C22+ ratio in n-alkanes, Pr/Ph ratio in isoprenoid alkenes, Ts/Tm in terpenes, and C-29 beta beta(alpha alpha + beta beta ) ratios in steranesare all better indicators in terms of maturity in pyrolysis. However, the maturity biomarkers ratios interpreted by the mechanism of isomerization such as C-31-homohopanes 22S/(22S+22R) and alpha alpha alpha C-29-sterane 20S/(20S + 20R), which had already reached their equilibrium values, indicating that microbiological deterioration is one reason for the failure indicative function of C(29)sterane20S/(20S + 20R) ratio. This research may also play an important role in the studies about the evolution of sedimentary organic matters in geology.