关键词: 珠江口盆地, 西江凹陷, 番禺4洼, 古近系, 高含砂率地层, 勘探突破, 大—中型油田

Abstract: Panyu4 subsag in the south of Xijiang sag in Pearl River Mouth Basin is proved to be rich in hydrocarbons. The early oil-gas exploration discoveries were mainly distributed in the middle and shallow strata above the Miocene Zhujiang Formation (buried depth less than 3 000 m). Recently, a major breakthrough has been made in the oil-gas exploration for Paleogene reservoirs in the middle and deep layers. Large and medium oilfields have been found in sand-rich strata of the Oligocene Zhuhai Formation and the Eocene Enping Formation in the Panyu10-6 structural belt. To further guide oil-gas exploration in the Eocene reservoirs of Panyu4 subsag, based on high-precision three-dimensional seismic, drilling and analytical data, this paper systematically studies the hydrocarbon source conditions, reservoir-cap assemblage, fault trap effectiveness and hydrocarbon accumulation mode of the Paleogene sandstone reservoirs in Panyu4 subsag, and summarizes the formation conditions and exploration direction of large and medium oil-gas fields in the Paleogene sand-rich strata in Pearl River Mouth Basin. The research results show that the extensive development of high-quality semi-deep to deep lake subfacies source rocks in Wenchang Formation provides a material basis for the large-scale accumulation of deep oil and gas. Braided river delta sandstones are developed in Enping Formation and Zhuhai Formation, which constitute two types of high-quality reservoir-cap assemblages with lake (sea)flooding mudstone and calcareous sandstone, respectively. Under the background of extension and strike-slip, the pressurization zone of transtensional fault and the calcareous cementation on the hanging wall of fault zone are beneficial to the lateral sealing of fault-block traps in the sand-rich strata. The main source faults adjacent to the structural belt determine the high-efficiency accumulation of oil and gas in short distance. The research results have effectively guided the discovery of large-medium oil-gas fields in Panyu10-6 structural belt, realized the exploration breakthrough in the new Paleogene strata of Panyu4 subsag, and revealed the exploration potential of the Paleogene hydrocarbon-rich subsag in Pearl River Mouth Basin, providing important reference for the exploration of the Paleogene sand-rich strata in other areas of Pearl River Mouth Basin.

Key words: Pearl River Mouth Basin, Xijiang sag, Panyu4 subsag, Paleogene, sand-rich stratum, exploration breakthrough, large and medium oilfield