琼东南盆地天然气成藏特征及地震识别技术
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摘要
琼东南盆地是南海北部大陆边缘的新生代伸展盆地,面积3×104km2。气源岩主要分布在中央坳陷带断陷期层序中(包括煤系和海相泥岩),具有早、晚两期生烃且以晚期为主的特征。天然气运聚成藏模式主要有3种:沿斜坡带侧向运聚成藏、沿断裂带垂向运聚成藏和强超压区盖层破裂式运聚成藏。圈闭形成有3期,早期(始新世—渐新世)形成的构造圈闭主要是与断层相关的背斜构造,中期(中新世)形成的构造圈闭主要是披覆背斜,晚期(上新世—全新世)形成的主要是挤压背斜。岩性圈闭和地层圈闭的形成与海平面变化和褶皱运动有关。早、中期形成的圈闭与晚期生排烃匹配较好。天然气勘探方向以凸起和低凸起边缘的构造为主,超压囊上部的岩性圈闭也是重要的勘探领域。近两年来,通过对琼东南盆地岩石物理参数进行统计分析和对地震资料作相对保幅处理,建立了盆地岩性、含气性与纵波阻抗、vp/vs(或泊松比)等地震岩石物理参数与地震响应的关系,在此基础上建立了琼东南盆地天然气地震识别技术体系和流程,为该盆地天然气层预测提供了有效的技术手段。
As an extensional basin,Qiongdongnan lies along the north margin of South China Sea,covering an area of 3×10~4km~2.Its gas source rocks occur mainly in the rifted-stage sequence of Central Sag belt(including coal measures and marine mudstone),and may be characterized by early and late two stages of hydrocarbon generation,with the late stage dominant.There are three patterns of gas migration and accumulation,i.e.lateral migration and accumulation along slope,vertical migration and accumulation through fault zones and seal-cracked migration and accumulation in overpressured areas.Structural traps may form in three different periods,with anticlines associated with faults in the early period(Eocene-Oligocene),drape structures in the middle period(Miocene) and compressive anticlines in the late period(Pliocene-Holocene).For lithologic and stratigraphic traps,their origination might relate to sea level changes and folding.The traps formed in the early and middle periods have a quite good match relationship with the late stage of hydrocarbon generation.Gas exploration should focus mainly on structures along the margins of uplifted or sub-uplifted areas,and the lithologic traps in upper overpressed chambers are also important targets.During the past two years,useful relationships were established between the basin's lithology and gas potential and the seismic responses of rocks,such as P-wave impedance and v_p/v_s ratio(or Poisson's ratio),by statistical analyses of petrophysical parameters and preserved amplitude processing of seismic data.Based on these relationships,a technical system and flowsheet of seismic gas identification have been set up in Qiongdongnan basin,providing an effective tool for the future gas predictions.
As an extensional basin,Qiongdongnan lies along the north margin of South China Sea,covering an area of 3×10~4km~2.Its gas source rocks occur mainly in the rifted-stage sequence of Central Sag belt(including coal measures and marine mudstone),and may be characterized by early and late two stages of hydrocarbon generation,with the late stage dominant.There are three patterns of gas migration and accumulation,i.e.lateral migration and accumulation along slope,vertical migration and accumulation through fault zones and seal-cracked migration and accumulation in overpressured areas.Structural traps may form in three different periods,with anticlines associated with faults in the early period(Eocene-Oligocene),drape structures in the middle period(Miocene) and compressive anticlines in the late period(Pliocene-Holocene).For lithologic and stratigraphic traps,their origination might relate to sea level changes and folding.The traps formed in the early and middle periods have a quite good match relationship with the late stage of hydrocarbon generation.Gas exploration should focus mainly on structures along the margins of uplifted or sub-uplifted areas,and the lithologic traps in upper overpressed chambers are also important targets.During the past two years,useful relationships were established between the basin's lithology and gas potential and the seismic responses of rocks,such as P-wave impedance and v_p/v_s ratio(or Poisson's ratio),by statistical analyses of petrophysical parameters and preserved amplitude processing of seismic data.Based on these relationships,a technical system and flowsheet of seismic gas identification have been set up in Qiongdongnan basin,providing an effective tool for the future gas predictions.
引文
[1]邱中建,龚再升.中国油气勘探[M].北京:地质出版社、石油工业出版社,1999:1164-1198.
[2]李绪宣,朱光辉.琼东南盆地断裂系统及其油气输导特征[J].中国海上油气,2005,17(1):1-7.
[3]龚再升等编著.中国近海大油气田[M].北京:石油工业出版社,1997.
[2]李绪宣,朱光辉.琼东南盆地断裂系统及其油气输导特征[J].中国海上油气,2005,17(1):1-7.
[3]龚再升等编著.中国近海大油气田[M].北京:石油工业出版社,1997.
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