Geochemical Characteristics And Oil-source Correlation Of Paleogene Source Rocks In Southern Dongpu Depression

Dongpu Depression is located in the southwestern margin of Bohai Bay Basin,which is part of Linqing-Dongpu Depression.Its west side overlaps the Neihuang Uplift.Its east side is bounded by the Lanliao Fault and the Luxi Uplift,its south is the Lankao Uplift,and its north is connected with the Shenxian Depression.Dongpu Depression,which spans Henan and Shandong provinces geographically,is anorth-eastward extension.Its south region is wide and north region is narrow.And the total area is about 5300 km².In this paper,the source rocks and crude oil samples in the southern part of the Paleogene in Dongpu Depression are taken as the main research objects.On the basis of collecting mud logging data,TOC and pyrolysis data,the distribution intervals of effective source rocks in the southern part of Dongpu Depression are identified.Based on the existing sedimentary facies research in the southern area,the organic phase characteristics of the mineral composition and organic matter of the rock are studied for the effective source rock distribution interval,and they are analyzed from the perspective of organic petrology and molecular geochemistry.The hydrocarbon generation characteristics of source rocks in the southern region are based on continuous sampling of longitudinal source rocks in the southern region,using saturatedhydrocarbonchromatography-massspectrometryandaromatics chromatography-mass spectrometry,scanning electron microscopy and other analytical methods to finely analyze different lithologic hydrocarbons in different environments.The molecular composition of the source rock lays a foundation for the anatomy of the oil source conditions in the typical oilfields of the southern region.The high-wax crude oil in the Machang area in the southern part of the Dongpu Depression is the main research object,the molecular composition of the crude oil in the southern Machang area is analyzed.And the crude oil maturity in this region is analyzed synthetically through a variety of molecular marker parameters,by using Gas Chromatography-Mass Spectrometry.The following main understandings have been achieved:1In the statistical results of geochemical data of source rocks in the southern Dongpu Depression,The hydrocarbon-generating potential?S1+S2?is mainly distributed in the range of 0.10-0.15 mg/g,with an average of 0.08 mg/g.Most of the Tmax values of source rocks in lower Es³ are mainly around 430°C.The Tmax values of the middle section of Es³1-4 and the middle section of Es³5-9 are mainly betweenthe kerogen of the II2 types.Overall,in the southern source rock samples,there are medium and rich hydrocarbon source layerin the lower section of Es³,which have certain hydrocarbon-generating potential and should be the main source hydrocarbon layer.2Most of the n-alkane distributions of the source rocks in the south showa single front peak state.A few source rocks with low thermal evolution source rocks have bimodal distribution.The content of high molecular weight n-alkanes is generally low,indicating that their maturity has basically reached the mature stage.The main source of organic matter is terrestrial lake-derived low-grade aquatic organisms.The pristane to phytane ratio is generally less than 1,which shows the characteristics of partial reduction of sedimentary environment.3 The maturity of crude oil in this area is comprehensively analyzed by various molecular marker parameters.From the analysis of saturated hydrocarbon parameters,it can be concluded that Ts/Tm mainly distributes in the range of 0.6-0.8,and most of them have entered the mature stage.The 22S/?22S+22R?parameter values are mostly between 0.52-0.58.The lower subsection of the third member of Shahejie Formation has exceeded the equilibrium point parameter values,and the maturity is relatively high,so it is not suitable to judge the maturity of the study area.Aromatic hydrocarbon parameter analysis shows that the content of triaromatic steroid detected in high wax crude oil samples in Machang area is relatively low,mainly ranged from 0.4%to 2.0%,which can be neglected.Most of the reference values of converted vitrinite reflectance calculated by Alkylphenanthrene parameter are 0.6%-1.0%,and the MDR values are basically between 4.0-6.0,which have a high maturity reference value,which is consistent with the actual research situation.Comprehensive evaluation shows that most of the high wax crude oils in Machang area in the south of Dongpu Depression are in mature stage.A few samples in the middle and lower sections of the third member of Shahejie Formation may be controlled by many factors,such as sedimentary environment and source,resulting in the maturity of individual crude oil samples being different from that of most samples.4 Oil source correlation between crude oil and source rocks in Nanmachang of the Yellow River is made.The distribution of tricyclic terpanes in high abundance source rocks and Machang crude oil samples in the lower key section of Es³ shows the normal distribution characteristics of C₂₃ dominance,while the homohopaneseries shows the stepped distribution;secondly,in the distribution of sterane,both source rocks and crude oil samples show the"L"distribution of C₂₇ dominance;moreover,the comparison of triaromatic steroid composition shows that Nanmachang crude oil of the Yellow River has a good relationship with the high abundance source rocks of the key source rocks in the lower section of Es³,while the difference between Nanmachang crude oil with the low abundance source rocks and the high abundance source rocks of the non-key source rocks is obvious.The relationship between the above saturated hydrocarbons and aromatic hydrocarbons reveals that Machang crude oil is obviously more likely to originate from the contribution of high abundance source rocks in the key hydrocarbon source layer of the lower section of Es³.At the same time,there is no relationship of oil-source correlation between Machang crude oil with high-abundance source rocks and low-abundance source rocks in non-key layer of the lower section of Es³.