Hydrocarbon Potential Of Source Rocks In Jurassic And Ordovician In Dagang Oilfield

The Jurassic and Ordovician systems are the oil and gas prospecting strata of the Dagang exploration area.Their source rocks and hydrocarbon generation potential are the main problems to be solved.Among them,the Jurassic system is the coal-sedimentary sedimentation in the background of fault depression.The recent drilling reveals some dark mudstones and inferior coal seams.The focus of this paper is on the degree of organic matter enrichment,thermal evolution and hydrocarbon generation potential.Drilling wells,this paper has carried out a new evaluation work using the Ordovician source rocks in the Ordos Basin.On the basis of previous studies,the focus is on the evaluation of source rocks in the Jurassic in Zhanghai and Xingang.Through core observation and geochemical analysis,it is considered that the lithology of source rocks（TOC>0.5%）is mainly coal,carbonaceous mudstone,dark mudstone,and the development of source rocks of Zhanghai 30-36 well and Xingang 1 well is es Tablelished.A histogram showing that the source rock develops in a dark coal-bearing combination in rivers,lakes,and marshes.The lithology and geochemical characteristics of source rocks were combined with logging and seismic information to es Tablelish a TOC and thickness prediction model for coal-series source rocks.It was found that 57.1%dark mudstones of the Middle-Lower Jurassic are potential source rocks,charcoal.The mudstone and coal rock are hydrocarbon source rocks with high organic matter abundance.Through the oil and gas generation thermal simulation experiment,the original TOC recovery and the oil and gas generation process analysis,the oil and gas generation intensity distribution map and hydrocarbon generation of different lithologic source rocks are made.It is found that the 415.2km² coal rock and the 325.88km² dark mudstone oil and gas intensity in Zhanghai and Xingang are 25×10⁴t/km² and 20×10⁸m³/km² respectively,which are effective source rocks,and the oil and gas generated is 23.58×10⁸t and 17.63×10⁸t;the carbonaceous mudstone oil production intensity is less than 20×10⁴t/km²,the gas intensity is>20×10⁸m³/km²,and only0.79×10¹²m³ natural gas is generated.These source rocks may form small-scale reserves（<200×10⁴t）.Oil and gas reservoirs.Through the full two-dimensional gas chromatography-flight mass spectrometry analysis of some core samples and Fangzi coal samples,it is found that the liquid oil n-alkane carbon number generated in C₁₃-C₃₃,main peak carbon C₁₈-C₁₉,the former and normal lake source rocks Consistent,the latter shows the characteristics of coal-based crude oil;according to the composition characteristics of naphthalene and phenanthrene series compounds,the discriminant index of Jurassic crude oil is proposed.According to the Ordovician source rocks in the Ordos Basin,the lower limit of organic carbon,TOC>0.3%,lithology and lithology characteristics,and limestone hydrocarbon generation characteristics,were studied for the Ordovician source rocks in the Dagang oilfield.A total of 241 geochemical data from 38 wells showed that 2.4%of the samples were source rocks.The maximum oil and gas strengths are 0.75×10⁴t/km²,17.57×10⁸m³/km²,respectively,and the effective source rock standard is not reached.Therefore,the Ordovician in the Dagang oilfield is not an oil source rock.