The Impact Of Overpressure Evolution Of The Bashijiqike Formation In The Kuqa Foreland Basin On Reservoir Pore Preservation

Recently,the Bashijiqike Formation in the Kuqa foreland Basin has found high quality reservoirs with abnormally thick layers and high pores.As an important factor for the preservation of pores in deep-ultra-deep reservoirs,the influence of overpressure evolution process on the preservation of pores in deep-ultra-deep reservoirs is still unclear.Therefore,on the basis of analyzing the pore types,physical characteristics and diagenetic evolution process of the target layer in the study area,the evolution process of formation overpressure and its evolution process,this paper uses numerical simulation method to recover the paleotectonic stress field,formation pressure evolution process and reservoir pore evolution process of Bashijiqike Formation in different structural sections of Kuqa foreland basin.The influence of abnormal pressure evolution on reservoir pore preservation in the study area is evaluated comprehensively.The results show that:(1)the pores of the target layer in the study area are relatively developed,and the primary pores are mainly developed.The reservoir has experienced diagenesis such as compaction,dissolution,cementation and metasomatism.(2)Overpressure is generally developed in the target strata of the study area.The present overpressure is mainly the result of the combined action of early undercompaction,late tectonic extrusion and overpressure transfer.(3)The study area experienced the strongest tectonic compression in the late Himalayan period,and different tectonic segments suffered different compressive strengths.The maximum horizontal principal stress of the target strata in the late Himalayan period in Keshen area was mainly distributed between 175～261MPa,and that in Dabei area was mainly distributed between 135～201MPa.(4)The overpressure development of the target layer in the study area has a positive influence on the reservoir pore preservation,and there are certain differences in the reservoir pore preservation effect among different structural sections.In Keshen area,about 2.64%～4.46% of reservoir pores are protected from compaction under the overpressure development.About 2.62%～4.23% of reservoir pores are protected from compaction in Dabei area.