CHARACTERISTICS OF FAULT ZONE STRUCTURE AND ITS RELATIONSHIP WITH HYDROCARBON MIGRATION AND ACCUMULATION: A CASE STUDY OF QIONGDONGNAN BASIN, SOUTH CHINA SEA

Qiongdongnan Basin is a Cenozoic petroliferous basin in the northern South China Sea. Because it is located at the junction of the Eurasian plate, the Pacific Plate plate and the India Australia plate, it is jointly affected by multiphase stress, and a large number of extensional faults are developed. Faults are important elements that transport natural gas and form structural traps. A fault is a three-dimensional geological body with a certain width, and its internal structure has strong heterogeneity. This research is based on core characteristics and logging curve response characteristics to carry out structural identification and division of fault zone. The structural development model of fault zone is established. Through experimental testing of fault rock samples, the physical characteristics and diagenetic cementation were analyzed. The structural characteristics of fault zone in Qiongdongnan basin and its relationship with hydrocarbon migration and accumulation are discussed. The results show that: (1) Fault zone can be divided into fault core and damage zone, and deep and shallow resistivity, caliper, porosity logging curves have good response characteristics to the structural division of fault zone; (2) The structure of fault zone is not necessarily well developed, and its development degree is greatly affected by the lithology of country rock, structural stress and fault activity. The structural characteristics of the same fault are heterogeneous; (3) The transmission and sealing of fault zone to oil and gas depend on the development degree of each structural unit of the fault, physical property conditions, diagenesis and the "time-space" matching relationship. The incomplete structure of the fault zone is a transport type fault zone, and the transmission capacity is controlled by the fracture density and connectivity. The complete structure of the fault zone is a sealed fault zone, and the transmission capacity depends on the matching relationship between diagenesis, main generation and expulsion periods and fault activity periods.

Acknowledge: The research was supported by special project for the operation of scientific research institutions in Shandong province (2021QNLM020001) and National Natural Science Foundation of China (42272155) .