Comparative Study On The Source Rock Geochemical Characteristics Of Natural Evolution And Thermal Simulation In Western Canada Sedimentary Basin

The thesis present study focuses on the natural evolution case history from the Second White Specks(2WS) Formation in Western Canada Sedimentary Basin(WCSB), which are from immature to high mature. Two Paleogene oil shale samples from Huadian Basin in Jilin Province and one immature sample from WCSB were conducted thermal simulation experiments in an autoclave. Geochemical characteristics in different evolution systems have been thoroughly investigated. These results provide deep understangding of petroleum generation and geochemical parameter variations.The samples from WCSB are characterized by high abundance of organic content with mainly type II kerogen, and the organic matter maturity increases with burial depth. The free hydrocarbon(S1) increases with increased depth and reaches its maximum at 2,600 m. However, the cracking hydrocarbon(S2) decreases with increased depth because S2 starts to be transformed into S1 and pyrobitumen.Molecular compositions of natural evolution and thermal simulation samples were analyzed by gas chromatograph-spectrometry after solvent extraction and fraction separation. The thermal simulation results show overall similarity to the natural evolution, which verify temperature as dominanat control for petroleum generation, whereas the obvious differences between two systems may indicate the role of time which cannot be simulated. The combination of two route provides deep understanding of petroleum generation and molecular parameter variation mechnisms. The absolute concentration rather than the ratio of the compounds is the keys to characterize the maturity system.By studying the relationship of methyl phenanthrene index, alkyl benzothiophene and the Tmax with known vitrinite reflectance of some samples, it finds out that methylphenanthrene index(MPI- 2) has the best correlation with Ro and the correlation coefficient is 0.93. Samples without vitrinite reflectance measurement can be ermprically derived from MPI-2. By studying Ro-depth correlation, it shows that Ro change non- linearly with the depth, which can be divided into three stages: slow increasing stage, medium increasing stage and rapidly increasing stage.The calculated transformation ratios of natural evolution samples from different methods are consistent: it has a wide range from 3% to 60% with buried depth up to 2000 m, then stabilized within 85%~90% deeper than 2500 m. The calculated transformation ratios of thermal simulation samples from different methods have the similar evolution trend with the North Sea Kimmeridgian source rocks, which are divided into three stages: the slow growth stage, the rapid growth stage and stable stage. But the results of transformation ratios from different methods are quite different. The initial transformation ratio from degradation rate theory reachs more than 90%, however, the one from slope theory reaches 36.6%, and it corresponds well with the productivity curves of samples, which proves that the transformation ratio from slope theory can reflect the main stage of hydrocarbon generation and expulsion better.