Prediction Of The Formation Pressure And Its Significance On Petroleum Geology In Block 4 Of The Central Junggar Basin

Abnormal formation pressure is a common phenomenon in petroliferous basins,which plays an important role in the generation,migration,accumulation and preservation of oil and gas.It has been proved by drilling that abnormal formation pressure exists widely in Block 4of the Central Junggar basin,and that the mechanism of overpressure is complicated.In this paper,the prediction of present formation pressure and the restoration of paleo-pressure evolution in Central Block 4 are carried out by using exploration data and various tested geochemical data,and the influence of overpressure on oil and gas accumulation is analyzed,and the following acknowledge are obtained:(1)In the methods of predicting formation pressure based on logging interval transit data,it is found that the pressure predicted by Eaton formula method and Bowers method is more consistent with the measured pressure at the same depth,and the Bowers method is not easy to be restricted by the relevant parameters,and the predicted pressure accuracy is higher,which is suitable for the calculation of overpressure caused by various causes.The D_C index generally deviates from the normal trend line in the direction of decreasing in the overpressure section.For the response of the relationship between D_C index and overpressure in some layers is not very obvious,the influence of other factors in drilling should be considered.(2)Based on the velocity data of seismic wave layer,the variation of section pressure can be predicted well.The prediction results of section pressure show that the overpressure section of the Central Block 4 has obvious low velocity characteristics,and the overpressure top interface has a certain transversal time.From the deep depression area to the slope area,the formation shows the trend of aging.(3)Fluid inclusion analysis and basin numerical simulation show that there are at least two periods of multi-stage petroleum filling process in the Central Block 4.The overpressure evolution of Jurassic started to increase about 180Ma?150Ma,and the pressure evolution is increasing up to now.The overpressure in Central Block 4 is mainly caused by hydrocarbon generation in the source rocks of Badaowan formation,and undercompaction has relatively little contribution to the formation of overpressure.The calculation of hydrocarbon generation pressurization shows that the hydrocarbon generation pressurization of the main hydrocarbon source rocks in Badaowan formation is a process in which there are at least two periods of increase in overpressure and one overpressure release.(4)From the section point of view,there are two sets of ultra-high pressure systems(Badaowan formation and Xishanyao formation)in the Jurassic of the Central Block 4.The overpressure in the Sangonghe formation is due to the transmission of the ultra-high pressure from the Badaowan formation to it,and the top boundary of the overpressure is near the Toutunhe formation.The accumulation of oil and gas in Toutunhe formation is due to the interaction of overpressure,large fault and sandstone transport layer of Sangongghe formation.From the plane,the oil and gas migration and accumulation from the southwest of the region to the east and northeast of the region are dominated by the overpressure of the Central Block 4.The tracer of dibenzothiophene parameters indicates that there may be two oil and gas filling paths in the north and south of the Tuantouhe formation in the Central Block 4,which are eastward in the direction of the north and the south.