Features Of Formation Pressure And Its Relationship With The Oil And Gas Distribution In The PH Structural Belt Of Xihu Sag

Overpressure phenomena are very common in the Pinghu formation of PH structural belt,which is located in the middle of the western slope zone of Xihu sag.The overpressure developed in the PH structural belt the most widely,which is the main production region of the Xihu sag,and there is a close relationship between abnormal high pressure and hydrocarbon distribution.Based on the Equivalent depth method,Eaton method and Bowers method as long as the measured formation pressure as calibration,the single well formation pressures are calculated.Combined with the lithology and the organic matter maturity,the single well formation pressure longitudinal section figures are made.Combined with the lithology,sedimentation rate,and organic matter maturity,based on the acoustic velocity-vertical effective stress,the single-well overpressure mechanisms are analyzed.According to all these work above,the formation pressure transverse and plane distribution characteristics are obtained.Combined with the oil,gas and water distribution and reservoir types,the relationships between formation pressure and oil and gas distribution in the PH structural belt and the favorable hydrocarbon enrichment are also discussed.?1?The Equivalent depth method is more suitable for the calculation of shallow formation pressure.For the deeper formation pressure,however,it is noneffective.For the pressure calculations in these areas,the Eaton method is the most useful one with the Eaton exponent of 1.3-1.6 which is roughly the same in the same area.?2?The abnormal high pressure top interface depth of the PH structural belt has significant differences in different tectonic zone.The abnormal high pressure top interface depth of Pingzhong zone began to appear in the 3300 m,geological horizon is three parts of Pinghu set,the abnormal high pressure top interface depth of Pingbei zone began to appear in the 3500 m,geological horizon is second parts of Pinghu set.?3?In PH structural belt,high pressure began to appear in second parts of Pinghu set,a total of four kinds of high pressure mechanism,the basic mechanism of E₂p² is undercompaction+hydrocarbon generation,the main mechanism of E₂p³ is hydrocarbon generation,undercompaction play a certain role in the causes of high pressure mechanism,the mechanism of E₂p³ and E₂p⁴ is hydrocarbon generation.Part of reservoirs developed high pressure,which high pressure mechanism is fluid conduction.?4?Oil and gas distribution in the study area has“oil above-gas blow”vertical distribution pattern.Condensate gas pool is main oil and gas pool in the study area.Oil and gas pool of Huagang formation is main light oil pool which is in normal pressure system.Condensate gas pool of Pinghu formation is in two sets of pressure system,roughly 3300m is boundary of two sets of pressure system in Pingzhong area,3700m is boundary of two sets of pressure system in Pingbei area.Condensate gas pool with normal pressure system is above the boundary,Condensate gas pool with abnormal high pressure system is blow the boundary.?5?Pinghu formation developed four types of oil gas reservoir in the study area,including double closed high pressure??_A type?,double closed pressure transition zone(?_B type),single closed pressure transition zone??_A type?and single closed normal pressure(?_B type),double closed high pressure and double closed pressure transition zone,are two main types of oil gas reservoir.Double closed pressure transition zone,single closed normal pressure zone and the top of double closed high pressure zone are the favorable zones where oil and gas accumulate in.?6?Pressure belt is a zonal distribution in the study area,the pressure coefficients changes quickly in the slope zone which shows good hydrocarbon migration and accumulation conditions.From Pinghu group second segment,not only high pressure distribution range becomes wide,but also high pressure growth rate increases gradually.High pressure of the Pinghu group fourth segment is the most widely scope of high pressure,and is also the biggest pressure development segment.Pressure coefficient from central sag to edge becomes smaller,finally becomes a normal hydrostatic pressure.In west secondary concave and PH structural belt,hydrocarbon formation with high pressure in the deep generated a lot of hydrocarbon,and then formatted high pressure,and then provided ample power for hydrocarbon migration.Oil and gas gathered in the pressure transition zone and pressure relief area.?7?In the study area,oil pool is main pools in Huagang group,mainly distributed in normal pressure zone,single closed normal pressure is its main formation pressure type.Condensate gas pool of E₂p^1-2 mainly distributed in normal pressure zone or pressure transition zone,single closed pressure transition zone and single closed normal pressure is its main formation pressure type.Condensate gas pool of E₂p^3-4 mainly distributed in pressure transition zone or high pressure zone,double closed pressure transition zone and double closed high pressure is its main formation pressure type.Condensate gas pool of double closed pressure transition zone have high oil and gas production.