台阶式断坡带砂砾岩体沉积过程模拟及其勘探启示——以东营凹陷胜坨地区沙河街组四段上亚段为例

为了厘清台阶式断坡带砂砾岩体的展布规律,建立合理可靠的沉积充填模式并有效指导勘探决策,以东营凹陷胜坨地区台阶式断坡为基底模型开展了水槽沉积模拟实验,并在实验中设计了交替发生泥石流、阵发性洪水和牵引流等沉积作用。研究结果表明:台阶式断坡带中主要发育近岸水下扇、浊积岩等砂砾岩体,其中,近岸水下扇分布在一台阶断坡带,扇体的沉积充填特征与前人提出的铲式断坡近岸水下扇的沉积充填特征基本一致,即早期填洼补齐、孤立发育,晚期迁移叠置、连片发育;二台阶主要发育浊积岩,其砂砾岩体在动态充填过程中表现为断层转换带、似湖底扇、越阶式和迁移叠置式等多类沉积充填类型。一台阶与二台阶的砂砾岩体存在成因联系。基于沉积过程和砂体发育规律的认识,胜坨地区二台阶的油气勘探再获突破。

Sedimentary process simulation and exploration implication of glutenite body in stepped fault-ramp zone:a case study of the upper submember of Member 4 of Shahejie Formation in Shengtuo area of Dongying sag

In order to investigate the distribution law of glutenite bodies in the stepped fault-ramp zone,establish a reasonable and reliable sedimentary filling pattern and effectively guide exploration decision-making,a flume sedimentation experiment was carried out with the stepped fault-ramp in Shengtuo area of Dongying sag as the base model,and the alternating sedimentary processes such as debris flow,paroxysmal flood,and traction flow was designed in the experiment.The results show as follows.The glutenite bodies such as nearshore subaqueous fans and turbidites are mainly developed in the stepped fault-ramp zone.The nearshore subaqueous fans are distributed in the first stepped fault-ramp zone,and the sedimentary filling characteristics of the fans are basically consistent with those of the shovel-like nearshore subaqueous fans in the fault ramp proposed by the predecessors.That is,the fan bodies fill the geodepressions and develop isolately in the early sedimentation stage,and then migrate and overlap to form larger contiguous regions in the late sedimentation stage.Turbidites are mainly developed in the second stepped fault-ramp zone.There are many dynamic filling types of glutenite bodies,such as fault transition zone filling,sublacustrine fan filling,step filling and migration-superposition filling.There is a genetic relationship between the glutenite bodies of the first and second stepped fault-ramp zone.Based on the understanding of sedimentary process and sand body development law,the oil-gas exploration has made another breakthrough in the second stepped fault-ramp zone of Shengtuo area.