The Formation And Evolution Of Fluid Dynamic Field And Its Effect On Hydrocarbon Accumulation In Southern Junggar Basin

As a fluid mineral,hydrocarbon migration and accumulation are mainly controlled by the characteristics of fluid dynamic field.Southern Junggar foreland sub-basin,located in the northern of Tianshan Mountains,is rich in hydrocarbon resources.Due to multiple periods of tectonic compression,faulting,and rapid uplift and subsidence of the basin,fluid pressure increases,and faults cause fluid and pressure conduction,which makes the composition and evolution of abnormal pressure of southern Junggar foreland sub-basin far more complex than other sedimentary basins.This thesis focused on southern Junggar foreland sub-basin as the research object.To highlight the impact of the tectonic compression process on the fluid dynamic field,including transfer overpressure and pressurization resulted from tectonic compression.By the means of basin simulation,coupling simulation of abnormal pressure with multiple causes,analyzing its impact on hydrocarbon migration and accumulation.The tectonic deformation during the late Himalayan period in the southern Junggar Basin was the strongest,and it was also a critical period for hydrocarbon accumulation.In the research,based on the analysis of the late Himalayan tectonic stress field,the boundary conditions and results of the section model are used as constraints to simulate the 3-D stress field.Furthermore,based on the analysis of rock stress and strain,comprehensively considering elastic deformation and plastic deformation,a quantitative evaluation model of the maximum and minimum values of tectonic compression pressurization is established.Finally,on the basis of fluid dynamics reconstruction of disequilibrium compaction and hydrocarbon generation,by setting the fault permeability and the period of fault activity,the evaluation results of tectonic compression pressurization are defined as boundary conditions to couple abnormal pressure of disequilibrium compaction,hydrocarbon generation,tectonic compression pressurization,and transfer overpressure.The abnormal pressure coupling simulation with multiple causes can more accurately describe the evolution of the fluid dynamic field during tectonic thrusting,erosion of high parts,and deposition of low parts in the late Himalayan.The main results are as follows:(1)The causes of overpressure in southern Junggar foreland sub-basin are mainly disequilibrium compaction,hydrocarbon generation,tectonic compression pressurization,and transfer overpressure.Disequilibrium compaction is widespread in southern Junggar Basin.Pressurization during hydrocarbon generation mainly occurs in the Jurassic and below strata,and the pressurization amplitude is small.Because the pressure system in the Huo-Ma-Tu anticline of the lower play is relatively closed,after the tectonic uplift,the high-value area of fluid pressure resulted from disequilibrium compaction and hydrocarbon generation migrates to the front of the Tianshan Mountains.(2)The magnitude of tectonic compression pressurization is related to the horizontal minimum principal stress during the maximum-fold period,petrophysical parameters,buried depth,and fluid pressure before tectonic compression.After considering the tectonic compression,the distribution pattern of fuild potential has changed significantly.Tectonic pressurization led to the expansion of the high flow potential zone to the thrust belt,and the gas potential gradients of Ziniquanzi Formation and Qingshuihe Formation are reduced,which provided a guarantee for hydrocarbon accumulation,meanwhile the Jurassic gas gradient increased,which was beneficial to lateral hydrocarbon migration.(3)The permeability of the faults,the period of fault activity and the overpressure difference between the source and the end have a relatively obvious impact on the transfer overpressure through faults.The fault activity communicates the deep and shallow fluid dynamics systems in the form of "seismic pumps",and efficiently transports deep overpressured fluid or hydrocarbon to the shallow layers.During the active period of the fault,the failure of the sealing of the shallow cap by the fault causes mass losses of oil and gas,which is the primary factor restricting the hydrocarbon accumulation of shallow in southern Junggar foreland sub-basin.(4)The coupling simulation of abnormal pressures with multiple causes can obtain more accurate fluid dynamic fields,and the location of oil and gas fields revealed by the simulation are more compatible with proven oil and gas fields.The evolution of the fluid dynamic field in the southern Junggar Basin indicates that the lower play is a favorable exploration area.Moreover,combined with static accumulation factors such as hydrocarbon source faults,reservoirs,traps,etc.,seven favorable areas are selected for the streamline accumulation area of the Qingshuihe Formation fluid potential,and the favorable area south of GQ1 has been confirmed.