“源热共控”澳大利亚西北大陆边缘油气田有序分布

澳大利亚西北大陆边缘是全球油气最富集的区域之一,研究其油气分布规律及主控因素有助于指导下一步的油气勘探。为此,基于8个沉积盆地近60年的勘探成果资料,分析了各盆地的油气地质条件和油气分布特征,发现该区油气田呈"近岸油""远岸气"有序分布,指出这一分布模式主要是受烃源岩和热演化程度的共同控制。进一步依据"源热共控"论,深入探讨了烃源岩的成烃规律和成烃模式,并指出了下一步的勘探方向。结论认为:①北卡纳文盆地发育3套烃源岩,即中—上三叠统海陆过渡相三角洲泥岩、下—中侏罗统海相/海陆过渡相三角洲泥岩和上侏罗统—下白垩统海相泥岩,而布劳斯和波拿巴盆地主要发育2套烃源岩,即下—中侏罗统海相/海陆过渡相三角洲泥岩和上侏罗统—下白垩统海相泥岩;②该区大地热流值从近岸带向远岸带增大,局部存在异常,烃源岩热演化程度随埋深增大而增高;③从近岸带向远岸带,有机质存在从生油向生气转化的趋势,未来找油的主要领域应在近岸带,找气的主要领域在远岸带,该区天然气资源潜力巨大。

Orderly distribution of oil and gas fields at the Australia Northwest Continental Margin jointly controlled by source rocks and thermal evolution degrees

The Australia Northwest Continental Margin is one of the regions with the most enriched oil and gas resources in the world, and the study and analysis on its oil and gas distribution rules and main control factors play a guiding role in further oil and gas exploration. Thus, analysis was performed on oil and gas geologic conditions and distribution characteristics of eight sedimentary basins based on 60 years of exploration results. It is indicated that oil and gas in this area are orderly distributed, namely, nearshore oil and offshore gas, and this distribution mode is mainly jointly controlled by source rocks and thermal evolution degrees. Based on this joint control theory, further discussion was conducted on hydrocarbon generating rules and modes of source rocks and the future exploration targets were proposed. The following conclusions were reached based on the above mentioned analysis and study. First, three sets of source rocks are developed in North Carnarvon Basin, i.e. Middle-Upper Triassic marine/continent transitional delta mudstones, Lower-Middle Jurassic marine/continent transitional delta mudstones and Upper Jurassic-Lower Cretaceous marine mudstones. And in the Brauss and Bonaparte Basins, two sets of source rocks are developed, including Lower-Middle Jurassic marine/continent transitional delta mudstones and Upper Jurassic-Lower Cretaceous marine mudstones. Second, geothermal heat flow value in this area increase from the nearshore belt to the offshore belt, with abnormity locally, and the source rock maturity rises with burial depth. And third, the organic matters from the nearshore belt to the offshore belt present the converting tendency from oil generation to gas generation. In this area, there are enormous natural gas resources. In the future, the oil searching shall be mainly conducted in nearshore belts and gas searching in offshore belts.