Study Of The Geochemistry And Biomarkers Of Source Rocks Belong To The Shahejie Formation Of Paleocene In Denan Region

Denan region lies in the north-east part of Linqing Basin. The recent petroleum exploration shows that there is immature oil resource in Denan region. Therefore, the studies of Denan region are both significant for oil exploration and petroleum geochemistry basic research. This study used some techniques such as organic geochemistry bulk composition combined with molecular geochemistry, source rock analysis and evaluation of organic petrology, carbon isotopes of organic matter, petroleum geology inference etc. The emphasis is mainly concentrated on the source rocks belong to the Shahejie formation of Pal eocene, including the source rock evaluation of Denan region, geochemistry of the source rock, biomarkers of immature oils and source rocks. Then the ancient geological environment was established and immature oil formation mechanism was proposed. Following results have been tentatively proposed in this thesis:1 ) Based on the Organic Petrology studies, most of source rocks in this region is belong to immature source rock. The organic matter type of Esibelongs to I- II₁] type kerogen. The organic matter of Es3 is in the range of II₁i- II₂ kerogen. The source rocks of Esi and Es4 have relatively bad organic matter type. From viewpoint of organic richness of source rocks, the source rocks of Es1 and Es3 can be regard as effective source rock. Based on the maturity, organic matter richness, organic type of source rocks, following order have been proposed based on quality of source rocks:2) The curve between Tmax and depth has been established. From the data of different wells, it indicates that most of the source rocks in this region belong to immature source rocks. The data also reflect the early generation of hydrocarbon in the source rocks.3) In the source rocks of Denan region, n-alkanes distribution shows double peaks pattern. This kind of distribution pattern is common in brackish and saline deposit. The predominance of C₁₆ and C₁₈ also reflects the source input of algae in this kind of environment.4) The characteristic of tricyclic terpane reflected the source input of algae. The predominance of 4-methylsterane and dinosterane, and the C₂₇-sterane predominance "V" distribution pattern all indicate the great contribution of algae source input. Based on the ratio of sterane C2920S/(20S+20R)and C29 α β β/( α β β+ααα) , the source rocks can be regarded as typical immature source rocks. The existence of hop- 17(2 1 )-ene approves this explanation.5) The aromatic fraction shows similar characteristic with saturate fraction ofsource rocks. The relatively high abundance of aromatic tricyclic terpane (diaromatic tricyclic terpane and triaromatic tricyclic terpane) and high abundance of aromatic steroid hydrocarbons reflected algae source input. The lower content of cadalene, retene, 1,7-dimethylphenanthrene show very limited source input from high plant input.6) From the relationship of carbon isotope composition of crude oil and source rocks. We can see that Es3 and Es4 source rocks contributes greatly to the formation of immature oil. Other oil source correlation also show that the immature oil originated from source rocks of Es3 and Es4 in this region.7) The existence of high abundance of sulfid in the mudstone indicate that that there is a relatively high salinity environment in source rocks which is favorable for algae growth. Sulfid also can be regarded as a marker of the action of sulfur bacteria.8) Based on research results, author postulated that early generation of hydrocarbons is closely related to the action of sulfur bacteria. Many kind of algae such as dinoflagellates, diatom, prynesiophytes etc have rich biological lipids which has lower polymerization. The action of sulfur bacteria leads to the combination of biological lipids and sulfur, and cause generating hydrocarbons in the early stage.