Study On The Identification And Prediction Method Of Overpressure In Xihu Depression

Overpressure is widely developed in Xihu depression,which has complicated formation mechanism.In this paper,a lot of documents about overpressure at China and abroad are investigated.The overpressure identification and pressure prediction methods are summarized,and applied in the middle part of Xihu depression.Through the analysis of the related geological conditions of overpressure,the overpressure in the study area is identified by the method of combined logging curve analysis,mud density and measured pressure analysis,and its causes are analyzed,and the pressure distribution and overpressure structure model are also analyzed.The overpressure of Pinghu Formation and Huagang Formation in acoustic logging and density logging combination chart displays 3 features: First,the inversion of sonic logging curve and density logging curve is reversed.,the western slope drilling is characterized by this characteristic;Second,there is stagnation(constant)in sonic logging and density logging,this kind of feature is found in west slope and west sub-concave.Third,acoustic logging and density logging conform to the normal trend,mainly in the central inversion structural belt.In addition,it is found that there are at least two types of pressure structures in the middle part of Xihu depression,such as atmospheric-overpressure and atmospheric-overpressure-atmospheric pressure structures.The overpressure of the west slope and the west sub-concave source rock in Xihu depression is the cause of the autogenous hydrocarbon supercharging,and the non-hydrocarbon source rock mudstone and reservoir overpressure are the causes of the adjacent source pressure conduction.The hydrocarbon source rock overpressure of the central inversion tectonic belt is the multiple causes of autogenous hydrocarbon supercharging and tectonic compression,On the basis of previous studies,the Fillippone method and its improved formula method,Bowers method and Eaton index method were applied to predict the overpressure in the study area.A multi method overpressure prediction model for different zones and horizons in the study area has been established.The results show that the Eaton method and Bowers method are more accurate than the Fillippone method in the study area,and the relative error is 4.5% and 4%,respectively.The pressure prediction model of Bowes method is slightly higher than that of Eaton method.Therefore,the Eaton method and Bowers method should be chosen to establish the pressure prediction model.