准噶尔盆地玛湖凹陷地层超压成因及其对物性的影响

Formation overpressure and its influence on physical properties in Mahu sag,Junggar Basin

利用实测地层压力与测井资料开展准噶尔盆地玛湖凹陷砾岩储层超压成因机理及压力分布特征研究.在此基础上,通过铸体薄片、地质、测井、试油等资料分析研究区超压对储层物性的影响,并用模拟地层变孔隙压力下的孔隙度-渗透率-电阻率岩石物理联测试验验证.研究认为,玛湖凹陷砾岩油层的超压主要由泥岩欠压实形成,超压改变了储层孔隙结构,增加了储层的连通性,变孔隙压力试验能较好的模拟地层超压.研究结果表明,储层孔隙度随孔隙压力增大而增大,但绝对值影响较小,在2%以内;渗透率随孔隙压力增大而增大,当孔隙压力系数达到临界值1.8时,储层孔隙结构突变致渗透率异常升高,这是研究区超压油层高渗透性、储层高产的原因;超压导致泥岩中形成大量的微裂隙,增加了束缚水的联系使得电阻率降低.研究结果揭示了准噶尔盆地玛湖凹陷超压地层成因及超压高产油层孔隙度、渗透率、电阻率的变化规律,为勘探开发提供重要的技术支持.

Based on the measured formation pressure and logging data,the overpressure mechanism and pressure distribution characteristics of conglomerate reservoir in Mahu sag of Junggar basin are studied.On this basis,the influence of overpressure on reservoir physical properties is analyzed by casting thin section,geology,logging and oil testing data,and verified by rock physical joint test of porosity permeability resistivity under simulated formation variable pore pressure.The results show that the overpressure of conglomerate reservoir in Mahu sag is mainly formed by the undercompaction of mudstone.The overpressure changes the pore structure of reservoir and increases the connectivity of reservoir.The results show that the porosity of the reservoir increases with the increase of pore pressure,but the absolute value has little influence,less than 2%;the permeability increases with the increase of pore pressure.When the pore pressure coefficient reaches the critical value of 1.8,the permeability increases abnormally due to the sudden change of pore structure,which is the reason of high permeability and high production of overpressured reservoirs in the study area;overpressure leads to the formation of a large number of microcracks in mudstone,which increases the connection of bound water and reduces the resistivity.The results reveal the genesis of overpressure formation and the variation law of porosity,permeability and resistivity of overpressure and high production reservoirs in Mahu sag of Junggar basin,which provides important technical support for exploration and development.