关键词: 南海北部, 深水区, 新凹陷, 石油领域突破, 顺德凹陷, 伸展-走滑作用

Abstract: Pearl River Mouth Basin is one of the main fields of oil-gas exploration in the north of the South China Sea. There is a low degree of early exploration and no drilling in Shunde sag, which is located in the west of Zhu Ⅱ depression. Based on the newly acquired 3D seismic data in Shunde sag and the drilling data in the surrounding area, the regional petroleum geology research has been carried out. Through analyzing the tectonic evolution and fracture characteristics of Shunde sag, the paper investigates its controlling on source rocks, reservoir-cap assemblages, trap characteristics, migration and accumulation conditions, establishes hydrocarbon accumulation models, and proposes favorable oil-gas migration directions. The results indicate that strong extension of the northern Shunde sag in the faulting period played a role in controlling the sag structure and the distribution of semi-deep lacustrine source rocks along the sag and slope, with two main hydrocarbon kitchens developed in the east and west. Moreover, the superposed effect of both extension and strike-slip in depression period controlled the large-scale fan delta, braided river delta, and a series of fault-plunging structure or fault block trap groups distributed along the fault zone. Additionally, the hydrocarbon migration and accumulation was controlled by the long-term active faults and a series of positive structures formed by extension and strike-slip action. Finally, the accumulation model controlled by extension and strike slip actions has been established; the nose-shaped structural belt near the sag, the southern slope zone, and the horst belt in the sag are predicted as the dominant hydrocarbon migration and accumulation directions in the northern Shunde sag. The Well W36a was drilled in the horst zone of the northern Shunde sag, from which oil layers with the thickness of over 45 m were discovered, and high production of industrial oil over 100 m³/d was obtained, thus realizing a significant breakthrough in the new deep-water sags and new fields of petroleum exploration in the northern South China Sea, and confirming the development of high-quality thick layered semi-deep lacustrine source rocks during the strong faulting period in the northern Shunde sag. This has important guidance and reference significance for oil exploration in Shunde sag and even the northern South China Sea and demonstrates the exploration prospects for the oilfield groups of billion tons in Shunde sag and other marginal sags.

Key words: northern South China Sea, deep water area, new sag, breakthrough in petroleum fields, Shunde sag, extensional-strike slip effect