乌石凹陷东洼伸展滑脱断裂演化特征及识别

Evolutionary characteristics and identification of extensional detachment faults in the eastern Wushi Sag

滑脱断裂在断陷盆地中普遍发育,对油气成藏具有重要控制作用。通过对乌石凹陷海底电缆地震资料的精细解释,在乌石凹陷东洼首次识别出伸展滑脱断裂体系,流二段厚层泥岩、高角度斜坡和渐新世强烈拉张作用分别是其发育的重要物质条件、几何学条件和动力学条件。基于平衡剖面分析将其形成过程划分为3个阶段:高角度正断层形成阶段、高角度正断层向低角度正断层递变阶段、低角度正断层上覆地层滑动阶段。基于伸展滑脱断裂在地震剖面上的几何学和运动学特征,建立了伸展滑脱断裂断距不协调、非三角形减薄以及非沉积超覆等3种典型识别标志,并总结了伸展滑脱断裂旋转型、非旋转型、叠瓦状构造型、双重构造型等4种构造样式。该研究对乌石凹陷油气勘探具有重要理论和指导意义。

Detachment faults are widely developed in faulted basins and play an important role in controlling oil and gas accumulation.Based on the fine interpretation of the seismic data of the submarine cables in Wushi Sag,the extensional detachment faults were identified in the eastern Wushi Sag for the first time.The thick mudstone in the second member of Liushagang Formation,the high angle slope and Oligocene strong tension are the important material conditions,geometric conditions and dynamic conditions for the development of extensional detachment faults.Based on the analysis of balanced profiles,their formation process can be divided into three stages:the formation stage of high angle normal fault,progressive stage from high angle normal fault to low angle normal fault,and sliding stage of overlying strata of low angle normal fault.Based on the geometric and kinematic characteristics of extensional detachment faults on seismic profiles,three typical identification marks of the extensional detachment faults are established,including uncoordinated fault displacement,non-triangular thinning and non-sedimentary overlap,and four structural styles of the extensional detachment faults are summarized,including rotary,non-rotary,imbricate and dual structural styles.This study has important theoretical and practical significance for oil and gas exploration in Wushi Sag.