Relationship Between Overpressure And Hydrocarbon Migration And Accumulation Of Jurassic In Central Junggar Basin

Overpressure affects the migration direction and spatial distribution of hydrocarbons in oil-gas basins,and plays an important role in the study of the mechanism and distribution of hydrocarbons accumulation.The Jurassic strata in the central of Junggar basin are overpressure developed and rich in hydrocarbons resources.It is important to clarify the overpressure characteristics and their relationship with oil and gas migration and accumulation in the study area.This paper studies the formation pressure characteristics,overpressure genesis and evolution process of Jurassic system in the middle of alignment area by means of formation pressure prediction,geochemical test analysis,fluid inclusion test analysis,Paleopressure recovery,basin simulation and other technical means.The results show that there are two overpressure systems in the middle of the area,Jurassic overpressure system and Permian overpressure system,and the overpressure top interface has the characteristics of the distribution of the strata.The formation pressure coefficient increases with the increase of the buried depth in the section,and has a trend of high in the south and low in the north in the plane.According to the number of pressure system and the magnitude of overpressure,the research area can be divided into single overpressure structure,bottom strong double overpressure structure and top strong double overpressure structure.Among them,the single overpressure structure mainly develops in Zhong 1 block,and the bottom strong double overpressure structure mainly develops in Zhong 3 block,the top strong double overpressure structure is mainly developed in Zhong 4 block.Overpressure in Jurassic formation is mainly the result of hydrocarbon generation,while overpressure in reservoir is conducted by overpressure fluid.The fluorescence color of reservoir inclusions can be roughly divided into blue white and orange yellow,which indicates that there are two reservoir forming periods in the study area:Late Cretaceous and Paleogene to Neogene.The simulation results of Petromod software show that there are three types of pressure evolution in the study area:pressurization relief mode,pressurization relief pressurization mode and pressurization strong pressurization mode.The main source rock series in the central Junggar basin are Permian and Jurassic,both of which developed overpressure,the hydrocarbon migration is mainly along the fault,and some areas have lateral movement along the sand body.In Zhong 1 and Zhong 3 blocks,the source rocks of Permian are mainly supplied with hydrocarbon,and the deep chase source fault is the main channel of oil and gas migration,and the pressure attenuation gradient of source and reservoir is small.The Zhong 2 and Zhong 4 block mainly supplied by Jurassic system are the intergranular fault sand body combination transport system,and the residual pressure attenuation gradient of source and reservoir is relatively large.According to the recovery of pore permeability and overpressure in reservoir forming period,the reservoir formation index is analyzed and matched with its oil bearing property.The results show that the larger the reservoir forming index,the better the oil and gas properties of the reservoir.Combined with the coupling relationship of oil and gas source,distribution of transport system,pressure attenuation in the process of oil and gas migration,and dynamic resistance of oil and gas charging during the accumulation period,three kinds of oil and gas migration and accumulation models under overpressure control are established in the central Junggar basin:’single overpressure structure-break pressure transmission-vertical far source reservoir forming mode’,’strong double overpressure at the bottom-fault sand transport-multi-source reservoir forming mode’,’top strong double overpressure-fault sand transport-near source accumulation mode’.