关键词: 大气田, 构造沉积演化, 成藏条件, 分布特点, 西北大陆架, 澳大利亚

Abstract: Exploration for oil and gas in the Passive Continental Margin has been a hot spot of the whole world, and achieves a lot. The Northwest Shelf of Australia is a world-class gas province with minor oil, with 82% gas and only 18% condensate and oil, while other areas in the Margin are dominated by oil. Until 2009, 20 giant gas fields have been found in three basins in Northwest Shelf of Australia. Although the Northwest Shelf has rich hydrocarbon resources, its extent of exploration and exploitation is still low. Therefore, it is worthy of research and exploration. Based on the tectono-depositional evolution of Passive Continental Margin, combined with geological data of giant gas fields, this paper analyzes the features of main source rocks, reservoirs and seals in basins, studies the formation of giant gas fields, and thoroughly analyzes the factors controlling their distribution. It is believed that main source rock is humic and prone to generate gas, and the maturity is high, thereby the features of the source rock determine that the Northwest Shelf of is a gas province. Moreover, the main reservoirs are marine delta sandstone with excellent physical property, and they are widely developed in the syn-rift. After the Cretaceous Period, a set of excellent regional seals were deposited in the Northwest Shelf. Source rock, reservoirs, seals were vertically contacted and partially combined effectively, which is essential to the formation of giant gas fields. The geographic distribution of giant gas fields varies a lot. Most giant gas fields concentrate in Exmouth Platform and Rankin Platform. Besides, and most of them are buried deeply. The periods of reservoirs are chiefly Upper Triassic and Lower and Middle Jurassic, and all the giant gas fields are beneath the Cretaceous regional seals.

Key words: giant gas field, tectono-depositional evolution, accumulation, distribution, Northwest Shelf, Australia