Study On Main Controlling Factors Of Oil Enrichment Of Chang9 Oil Reservoir In The Yanchang Formation In Area C Of Ordos Basin

The Yanchang FormationTriassic of Ordos Basin is rich in tight oil resources and has great potential and prospect for exploration.The tight oil of the basin is mainly distributed in the Chang4+5,Chang6,Chang7,Chang8 and Chang9 oil Groups.As the oil and gas exploration under the Yanchang Formation of Ordos Basin is deepening,the tight reservoir under the Chang9 Formation has been found.At present,the main control factors and the distribution law of oil in the tight reservoir of Chang9 reservoir formation are not clear.In this paper,the case study of Chang 9 in the central and western part of Ordos Basin is given.The main controlling factors of oil enrichment in Chang9oil Group are summarized by studying the geological conditions,accumulation mechanism and relation with oil distribution.In order to further understand the formation process of tight oil in Ordos basin,provide guidance for tight oil exploration.Regional background data are used to summarize and study the source direction of the Chang 9 oil Group,and the sedimentary facies signs such as the color,grain size analysis,sedimentary structure and so on are used to determine the sedimentary facies types of the Chang9oil Group and analyze the characteristics of the sedimentary facies distribution.The petrologic features of reservoir,physical characteristics,diagenesis,microsmic pore-throat characteristics of reservoir,type of reservoirare analyzed using the data casting thin sections,scanning electron microscope.Using well logging,logging and testing data to determine the lower limit standard of effective reservoir in Chang9oil Group and analyze the plane distribution characteristics of effective reservoir.Fluid dymics processes of tight oil migration and accumulation are comprehensively analyzed using the combination of paleopressure calculate from the data of the interval transit time.Summarize the stage of formation of Chang9 oil Group by previous research.The oil migration channel types of Chang 9 oil Group in the study area are summarized using the previous research results,sand thickness and distribution characteristics and so on.Finally,the correlation between the geological conditions of reservoir formation and the distribution characteristics of petroleum in Chang 9oil Group is analyzed,and then the main reservoir controlling factors of tight oil in Chang 9oil Group are selected.The research results show that:The sedimentary facies of Chang 9 oil Group mainly consists of delta front sedimentary subfacies,and the sedimentary microfacies,such as underwater distributary channel,shunt bay and mat sand,are developed,and underwater distributary channel sand body is the main storage space.The lithology of Chang9 oil Group mainly consists of fine feldspar sandstone,medium-fine feldspar sandstone and fine-medium feldspar sandstone.The mineral composition is mainly feldspar and the quartz content is second.The reservoir porosity is mainly distributed in 2%⁸%,and the reservoir permeability is mainly distributed in 0.01×10^-3?m2⁰.3×10^-3?m2.The main storage space is primary intergranular pore,followed by dissolution pore.The main types of pore structure of reservoir are medium and small pores,and the main types of pore and larynx structure are mesoporous and micropore and microlaryngeal.The reservoir is distributed from the ultra-low permeability layer to the tight layer.The main types of reservoir are the IV_a and IV_b,which are the ultra-low permeability and ultra-low permeability reservoirs.The effective reservoir thickness in the Chang 9 oil Group is mainly about 3 m,the area with better local development can be 7 m,and the plane spreading is mainly in the North-South-West direction.source of migration dynamics is overpressure of Chang 7,Chang 9 source rock.The migration channel is mainly sand with relatively high porosity and high permeability,and the cracks play an improved role.The superimposed oil-bearing area in the Chang 9 oil layer is 53.65 km²,of which 23.16 km² in the Chang 9^1-1 layer,20.3 km² in the Chang 9^1-2 layer and 35.5 km² in the9^2-1 layer.The Chang 9 reservoir is a lithologic reservoir,which is mainly controlled by lithology and physical property.It is concluded that the main controlling factors of reservoir are good sedimentary facies zone and high quality effective reservoir.