The Rupture Of The Seal Of Pressure Compartment And Its Effect On Hydrocarbon Accumulation In Eastern Kuqa Depression

The seal is boundary of fluid pressure compartment,and it can make the fluid pressure compartment become an independent pressure system(open to the inside,closed to the outside).In addition,seal of fluid pressure compartment is an important basis for the division of oil-gas migration and accumulation system.It will cause the high pressure fluid in the compartment to leak out and remigrate,while the seal breaks.Therefore,it is great significance to study the rupture mechanism of the seal and expound its influence on the preservation and destruction of the fluid pressure compartment,hydrocarbon migration and accumulation.In this paper,the Dibei slope zone in the eastern Kuqa Depression is taken as the key research object,seals and its lithological characteristics,longitudinal pressure characteristics,sealing ability are determined and discussed by using drilling and completion,well logging,oil test data and downhole testing.There are two main rupture modes in the seal: fault and overpressure fracture.Therefore,the fault distribution and development characteristics are studied,and the loading curve method is used to identify the pressure transfer phenomenon caused by the fault.The overpressure fracture of the seal is studied by using the numerical simulation to restore regional stress field,combining with the feature of overpressure,and introducting the failure criterion of rock.Finally,the accumulation model under the condition of seal rupture is discussed and the following understandings are obtained:(1)The seal of pressure compartment is controlled by stratum obviously,and the three most prominent seal are pasty salt and pasty mudstone of Jidike formation,thick layer mudstone of Shushanhe formation,the thick mudstone strata of Yangxia coal strata.The mudstone layer of Yangxia formation at the top of the lower Jurassic high pressure gas reservoir is thick and stable,with high displacement pressure and overpressure.It is also the source rock of the high pressure gas reservoir,so it is considered as a good seal without rupturing.(2)There are three main fault zones in the east of kuqa depression,which are northern Yiqikelike fault zone,Dibei fault zone and eastern Tugeerming fault zone.There are three types about fault-break relationship between the fault and the seal:the fault extend to the surface and crossed salt bed,the fault under the salt bed and crossed Yangxia seal,the fault inside lower Jurassic pressure compartmentr.However,the pressure transfer phenomenon mainly occurs in the subsalt faultarea near the Dibei fault zone.(3)The numerical simulation results show that the maximum effective principal stress is about 80 MPa,the minimum effective principal stress is about25 MPa,during the late Himalayan movemwnt,in the Dibei slope zone.And the overpressure in the reservoir of the Ahe formation was 30~36 MPa.The results show that overpressure rupture happened in seal during the late Himalayan movement and keep the integrity in the current by combining with the stress characteristics of the seal,the overpressure in lower Jurassic pressure compartment and the rock rupture conditions modified by Griffith criterion.(4)There is early oil charged and late gas heavily charged in eastern Kuqa Depression.Including oil and gas charged event during sedimentary period of the Jidike formation and the gas charged event at the end of kuqa formation.Hydrocarbon further migration to shallow subsalt reservoirs or surface leakage by large faults.Small faults will accelerate the migration and accumulation of hydrocarbon in the lower Jurassic.Overpressure fracture of seal of pressure compartment occurred in the late Himalayan movement,it caused hydrocarbon leakage.And current overpressure fracture is closed.The seal of pressure compartment restores its sealing ability,and contributes to the formation of tight gas reservoirs in the ahe formation.