Exploration potential of marine source rocks oil-gas reservoirs in China

摘要

There is broad exploration potential of oil-gas generated from marine source rocks because of its generally lower exploration degree in China. So far, rather more marine oil-gas reservoirs have been found onshore as in Tarim basin, Sichuan basin, Erdos basin, Bohai Bay basin, North Jiangsu basin and offshore as in East China Sea (ECS) shelf basin, many Tertiary basins in South China Sea (SCS) such as Yin'ge Sea basin, Southeast Hainan basin, West Taiwan basin, Southwest Taiwan basin, Wan basin and Zenmu basin (East Natuna Basin and Sarawak Basin). The marine source rocks in these basins are mainly Paleozoic and Mesozoic onshore whereas Tertiary offshore. Three genetic categories of oil-gas reservoirs have been defined to the marine reservoirs in China as primary reservoirs, secondary reservoirs and hydrocarbon-regeneration reservoirs which formed by the second times hydrocarbon generation of marine source rocks. And three exploration prospects have also been suggested: ①primary reservoirs prospects, are chiefly distributed in many Tertiary basins of SCS, the Tertiary shelf basin of ECS and the Paleozoic of Erdos basin onshore. To explore the large-middle scale even oversize reservoirs should chiefly be considered in these category reservoirs. These basins are the most hopeful areas to explore the marine oil-gas reservoirs in China, among which especially the many Tertiary basins of SCS should be strengthened to explore; ②secondary reservoirs prospects, are mainly distributed in Paleozoic and Mesozoic of Tarim basin, Sichuan basin, Qiangtang basin and Cuxiong basin in western China, of which exploration potential is less than primary reservoirs. The formation of primary reservoirs and its secondary reservoirs is generally controlled by successive paleo-uplift, and the reservoirs are chiefly distributed at the upper part of slope transitioned from paleo-uplift to its adjacent hydrocarbon generation depression. Many bitumen beds (paleo-reservoirs) found in Tarim basin, Sichuan basin and southern China chiefly belong to relics of destroyed primary oil-gas reservoirs, ③hydrocarbon-regeneration reservoirs prospects, are chiefly distributed in Bohai Bay basin, North Jiangsu -South Yellow Sea basin, Southern North China basin, Jianghan basin, South Poyang basin in eastern China and Tarim basin, of which source rocks are generally the Paleozoic. And the reservoirs formed by the later stage's (always Cenozoic) second times hydrocarbon generation of the Paleozoic source rocks should mainly be considered to explore, among which middle-small and small reservoirs are the chief exploration targets. The distribution of hydrocarbon-regeneration reservoirs is generally controlled by the second times hydrocarbon generation center or later stage hydrocarbon generation center of Paleozoic & Mesozoic sources rocks. Because of particularity and activity of China continent tectonic, the marine reservoirs onshore chiefly belong to secondary and hydrocarbon-regeneration categories, but much less primary reservoirs. As a result of higher thermal evolution of' Paleozoic & Mesozoic source rocks, the marine reservoirs onshore are mainly gas fields, and so far the marine oil fields have only been found in Tarim basin. Considering the status of higher exploration degree of continental oil & gas of which residual resource gradually decreases in China, the exploration & development to marine genetic oil & gas should be fortified. No other than establishing corresponding marine oil-gas exploration & development strategy and policy, sufficiently enhancing cognition to the particularity and complexity of China marine petroleum geology, and applying new thoughts, new theories and new technologies, at the same time tackling some key technologies, it is possible to fast effectual exploit and utilize the huge marine oil-gas resource of China.