Tight Oil Accumulation Characteristics Of Da'anzhai Member Of Gongshanmiao Oilfield In Central Sichuan

Gongshanmiao oilfield is located in the central area of Sichuan basin.It is in Yingshan tectonic group of northern flattish tectonic belt with an area of about 560km2.It is one of the five main oil fields that have been found in Sichuan area.The main oil production layer of the lower Jurassic Daanzhai is a typical unconventional tight limestone reservoir.The thesis is based on the petroleum geology,reservoir geology,and geochemistry of oil and gas theory,with modern analytical methods.based on analyzing the stratigraphic characteristics,structural characteristics,through the study of characteristics of source rocks and oil source correlation,reservoir characteristics and reservoir migration conditions,detailed summary of the work area density limestone reservoir reservoir geological conditions,the accumulation period and main controlling factors of oil and gas,and establish reservoir model.Research shows that:the Da'anzhai formation is stable.It is divided into 3 sub sections of the first,the second,and the third.The first section is clay bearing shell limestone and black shale interbedded grayish brown shell limestone.The second sub section is mainly thick black shale,which is the Da'anzhai main oil-bearing stratum.The third section is the main reservoir reservoir,which is mainly the thick massive brown shell limestone with thin layers of black shale.The Da'an Zhai segment is a tight limestone reservoir with poor physical properties.It is a very low porosity and low permeability reservoir.The reservoir space types of Da'an Zhai reservoir mainly composed of four types,including micropores,microfractures,macropores and fractures.In terms of origin,they are mainly structural joints and secondary dissolution pores.The thickness of the Da'an Zhai source rock is 30?70m.The abundance of organic matter in the second subsection is relatively good source rock,and the organic matter is type ???2,followed by the first subsection,the abundance of organic matter is differential medium source rock,the organic matter is type ?1??,and the third subsection,the organic matter is a differential source rock,and the organic matter is type ?2??.Based on the comprehensive analysis of maturity of organic matter in source rocks,it is believed that the source rocks of the Da'an Zhai segment of the main reservoir are mainly in the peak period of oil generation.According to the oil source comparison,the crude oil mainly originates from the self generating and self storage of the Da'an block,and has the characteristics of the near source aggregation.According to the characteristics of the whole oil chromatographic fingerprint,the crude oil composition of Da'an Zhai section has a large lateral variation,and the difference between wells is obvious,and the heterogeneity is strong.The main oil and gas charging power is the maximum residual pressure.The maximum residual pressure in the study area is characterized by the high level in the southwest and the low in the northeast.The main oil and gas are vertical migration through pore,micro crack and wide crack.We induce reservoir geological conditions,determine the accumulation stage,analysis of main controlling factors of hydrocarbon accumulation and sum up the reservoir forming model.The second section of the basin source rocks developed well,has sufficient oil source.The crust and limestone reservoirs in the first and the third section are tight and poor in physical properties,but the oil content is relatively good.Fracture is the main channel of oil and gas migration,and large fracture is not conducive to oil and gas migration and accumulation.The source and reservoir interbeds are beneficial to the migration and accumulation of oil and gas.Combined with the simulation experiments of sedimentary burial history,thermal evolution history,tectonism and reservoir forming dynamics,it is considered that the peak period of petroleum generation is in Yanshan period,and the distance of oil and gas migration is short,which is near source charging.The reservoir has been densified,and the tight oil is transported to the reservoir in the reservoir with better reservoir space,and the inner structure of the basin eventually forms the late Himalayan tectonic movement.