先存隐伏断裂识别方法及应用——以南海北部惠州–北卫滩断裂为例

Identification Method and Application of Pre-Existing Hidden Faults—A Case Study of the Huizhou-Beiweitan Fault in the Northern South China Sea

摘要: 先存隐伏断裂是指形成于早期地质时期、后期被沉积物或岩层覆盖且可能再次活动的断裂构造。珠江口盆地惠州凹陷是我国南海北部重要的富生烃凹陷，近年来随着盆地勘探领域逐步由浅层向深层转变，先存隐伏断裂的形成演化及其控洼作用研究尤为重要，其中惠州–北卫滩断裂是惠州凹陷西部典型的NW向先存隐伏断裂，而目前对于断裂的识别标志、发育模式的认识极为不足。本文综合运用重磁异常与三维地震资料，系统开展了隐伏断裂识别与构造解析研究，总结了先存隐伏断裂的发育特征及其识别标志。惠州–北卫滩断裂在珠一坳陷发育位置在西江23洼东侧–惠州24洼–惠州26洼一带，影响范围基本覆盖整个惠西地区，向南延伸至南部低隆起东界。断裂于惠州凹陷内的地震剖面上发育“Y”字形构造及似花状构造。根据各时期断裂活动分析表明在古近系拉张应力由NW–SE向顺时针转变为N-S向的过程中，断裂与应力方向夹角不断增大，整体经历了前新生代先存形成–早文昌张扭活化–晚文昌继承活动–恩平期张性拓展的演化过程。同时，惠州–北卫滩断裂在新生代的活动控制了惠西地区洼陷的构造样式与沉积迁移。

Abstract: Pre-existing hidden faults refer to fault structures that formed in early geological periods, were later covered by sediments or rock layers, and may be reactivated. The Huizhou Sag in the Pearl River Mouth Basin is an important hydrocarbon-rich sag in the northern part of the South China Sea. In recent years, as the exploration scope of the basin has gradually shifted from shallow to deep layers, research on the formation and evolution of pre-existing hidden faults and their depression-controlling effects has become particularly important. Among these faults, the Huizhou-Beweitan Fault is a typical NW-trending pre-existing hidden fault in the western part of the Huizhou Sag. However, the current understanding of the fault’s identification markers and development patterns is extremely insufficient. In this study, gravity-magnetic anomalies and 3D seismic data were comprehensively used to systematically conduct research on concealed fault identification and structural analysis, and the development characteristics and identification markers of pre-existing hidden faults were summarized. The Huizhou-Beweitan Fault is developed in the Zhu I Depression, distributed along the area from the east of Xijiang 23 subsag, through Huizhou 24 subsag to Huizhou 26 subsag. Its influence range basically covers the entire western Huizhou Sag and extends southward to the eastern boundary of the southern low uplift. On the seismic profiles within the Huizhou Sag, the fault develops “Y”-shaped structures and flower-like structures. Analysis of fault activity in various periods shows that during the Paleogene, when the extensional stress direction rotated clockwise from NW-SE to N-S, the angle between the fault and the stress direction increased continuously. The fault has undergone an evolutionary process of pre-Cenozoic pre-existing formation-early Wenchang Stage tensional-shear reactivation-late Wenchang Stage inherited activity-Enping Stage extensional expansion. Meanwhile, the activity of the Huizhou-Beweitan Fault in the Cenozoic controlled the structural patterns of sags and sedimentary migration in the western Huizhou Sag.