南海第三纪生物礁及其含油气性

TERTIARY REEFS OF THE SOUTH CHINA SEAS AND THEIR OIL-GAS BEARING CHARACTERS

本文收集我国和周边国家大量的油气勘探资料,综合分析南海沉积盆地第三纪生物礁的分布、类型和岩性特征,探讨了珠江口盆地、莺歌海盆地、琼东南盆地、万安盆地、曾母盆地和巴拉望盆地生物礁的含油气性,认识到良好的生、储、盖组合和运、圈、保各项条件较好又能彼此配合,可使盆地具很好的含油气性,而礁体储油物性和生油岩的好坏又是含油气性评价的关键因素,有利的圈闭条件和运移条件也是重要的影响因素。通过分析热认为。本区各盆地第三纪生物礁的含油气性可分为三等:珠江口盆地和曾母盆地最好,万安盆地和巴拉望盆地次之。莺歌海盆地和琼东南盆地较为逊色。

There are various types of Tertiary reefs in basins of the South China Seas; and the reefs developing in Zhujiangkou Basin, Yinggehai Basin, Qiongdongnan Basin, Wan'an Basin, Zengmu Basin and Balawang Basin are of good conditions of oil and gas accumulation. The research result shows the difference of the distribution, type and lithology of the Tertiary reefs of the South China Seas and the characters of the migration, trap and preserve. The reefs of these basins are of different oil-gas bearing characters. The oil-gas accumulation capacities of these reefs in the basins can be separated into three varying degrees, that is, Zhujiangkou Basin and Zengmu Basin are the best; Wanan Basin and Balawang Basin are the second; Yinggehai Basin and Qiongdongnan Basin are the third. The three oil-generating beds in Zhujiangkou Basin are Eocene, Oligocene and lower Miocene strata with lacustrine shale and argillites, which are of good oil-productive capacity. The three early-late Miocene reefs with grainstones, packstones, wackestones, etc., which are situated in the Shenhu Uplift and Dongsha Uplift, are characterized by high porosity and high permeability, so that they can become fine reservoirs. Meanwhile, the middle Miocene mudstone of 500～895m thickness is regional capping bed. Combining with the fine qualification of oil-gas migration, trap and preserve, these uplifts became advantageous oil-gas gathering reef-zones. The middle-Miocene reefs in Yinggehai Basin grew in the littoral area near the lower Tertiary resource bed with average TOC 1.95% and Ⅱ kerogen. The reef reservoirs are of low permeability because of the little thickness and the lack of the secondary pores. The distribution of early-middle Miocene reefs, such as atolls and platform fringe reefs in Qiongdongnan Basin, was obviously controlled by the basement fractures. The physical property of reef reservoirs, like Yinggehai Basin, is not good. The various types of middle-late Miocene reefs in Zengmu Basin characterized by large areas and thickness and high porosity and permeability, which are fine reservoirs. There are well conditions of oil-gas migration, trap and preserve together with the combination of the source, reservoir and capping rocks giving rise to the formation of the reef oil-gas agglomerate zones in this basin. The developing time of the reefs of Balawang Basin was in middle-late oligocene and Nidou Reef located in the north of this basin is a large reef oil-gas field. There are many Tertiary reefs in Wanan Basin and oil fied development is been going in these reefs now. The component factor of the source, reservoir and capping is fine in this basin, but there is no condition for the long-distance migration, resulting in the invalid traps far from the source rocks.