Hydrocarbon Accumulation Conditions Of Yanchang Formation In Fuxian Area,Ordos Basin

By analyzing a large number of drilling logs,cores and experimental data in the study area,the size and quality of the hydrocarbon source are analyzed,and the geochemical characteristics of the source rocks are analyzed,thereby comparing the oil and gas sources of the extended group.The fluid inclusion temperature measurement method combined with the burial history and thermal history analysis of the formation determines the time and time of hydrocarbon accumulation,and combines the results of illite dating to prove the accuracy of hydrocarbon accumulation time.Source rock evaluation and resource potential analysis were carried out based on organic abundance,kerogen type,crude oil composition,and effective source rock thickness.Based on the reservoir profile,the basic elements of hydrocarbon accumulation,trap conditions and preservation conditions are analyzed,the migration and accumulation process of oil and gas are clarified,and the reservoir formation model is established,which lays a geological foundation for the next oil and gas exploration.There are three sets of source rocks in the Fuxian area,which are the Chang 6 section with a small amount of black shale,the Zhangjiatan shale at the bottom of the Chang 7 section,and the black mudstone at the bottom of the Chang 8 section.The organic abundance of these three sets of shale is good,and they all reach the maturity stage.The kerogen types of the Chang 7section and Chang 8 section are mostly humus-soybean-type,and the Chang 6 section is mostly humic-soil-to-soil-humic type.The three sets of shale have the best quality in the Chang 7section,and have large thickness,wide distribution and great potential for hydrocarbon generation.Comprehensive geochemical analysis data,from the group composition,saturated hydrocarbon gas chromatography and biomarker compounds,comprehensively analyzed the geochemistry of the Chang 8-Chang 6 layer crude oil and source rocks of the Triassic Yanchang Formation in Fuxian area,Ordos Basin.Characteristics to analyze the oil and gas exploration prospects in the area.The analytical variable parameters are parameters such as Pr/Ph,Ph/n C₁₈,Pr/n C₁₇,OEP ratio in saturated hydrocarbon chromatography.The light/heavy ratio and Ph/n C₁₈and Pr/n C₁₇ of Chang 6 section and Chang 7 section are relatively close,reflecting similar sources.The distribution characteristics of normal paraffins are unimodal,the main peak carbon is C₁₈?C₂₀,and the content of gamma wax is generally low,which indicates that the environment in which source rocks develop is not a strong reduction environment.The most striking feature of the decane compounds in the Fuxian area of the Ordos Basin is that the regular decane has an asymmetric"V"shape distribution in the C₂₇,C₂₈,and C₂₉ series.Based on the analysis of the source rock conditions,reservoir conditions and capping conditions of the Yanchang Formation in Fuxian area,it is concluded that three favorable sets of reservoirs and reservoirs are formed in the longitudinal direction of the study area.The accumulation model can be divided into upper reservoirs.There are three types of self-storing and subsistence storage.The oil source of the 7th and 9th sections is transported to the Chang6 or Chang 8 reservoir through cracks,micro-cracks,sand body stacking points and mudstone tipping points.Some of them are directly integrated in the long 7 clusters.The reservoir-forming model in the study area has the characteristics of near-integration and accumulation,and has favorable conditions for forming large and medium-sized gas fields.