澳大利亚西北陆架深水盆地油气地质特征

HYDROCARBON GEOLOGICAL FEATURES OF DEEPWATER BASINS ON NORTHWEST SHELF OF AUSTRALIA

澳大利亚西北陆架贫油富气,在近年的勘探开发中显示出广阔的前景。通过对澳大利亚西北陆架大量相关文献的分析总结,区域上包括4个盆地和1个造山带:北卡那封盆地、柔布克盆地、布劳斯盆地、波拿巴盆地和帝汶-班达褶皱带。西北陆架属边缘海型被动大陆边缘,构造演化经历了前裂谷期、裂谷期和被动大陆边缘期三大阶段,对应发育有三大沉积建造层序。西北陆架的油气绝大多数集中在中生界,且呈现"内油外气,上油下气"的分布特点。发育三套主要烃源岩:三叠系湖相泥页岩、侏罗系海陆过渡相碳质泥岩和煤系及海相泥岩及下白垩统海相泥页岩,烃源岩样品显示其大多具生气能力,揭示了形成烃源岩的4种模式;主力储集层为裂谷期海相砂岩,被动陆缘期白垩系浊积砂岩是潜在储层;下白垩统海相泥页岩是区域性盖层。根据形成储盖组合的沉积环境,主要发育海相型、海陆过渡相型和陆相型三大储盖组合类型,海陆过渡相型储盖组合是区域主要的成藏组合。油气运移的方式主要有构造脊运移、垂向运移和不整合面侧向运移,超压、断层和不整合面是本区影响运移的主要因素。油气成藏以近源下生上储占主导。随着勘探技术的进步,本区油气勘探前景广阔。

The North West Shelf of Australia is a world known gas province with great potential having proved by the exploration and exploitation in recent years.It is a typical passive margin of a marginal sea consisting of four basins and an orogenic zone,namely the North Carnarvon basin,Roebuck basin,Browse basin,Bonaparte basin and the Timor-Banda orogenic zone.It has experienced three stages of evolution,i.e.,the pre-rift stage from the Cambrian to Early Jurassic,the rift stage from the Early Jurassic to Early Cretaceous and the passive continental margin stage from the Early Cretaceous up to present.Correspondingly there are three suits of sedimentary sequences.Most of hydrocarbon is accumulated in the Mesozoic,with gas in the outer part and lower sequence,and oil in the inner part and upper sequence.3 types of source rocks are recognized.They are the Triassic lacustrine shale,Jurassic paralic carbonaceous argilite,coal bearing strata and marine shale,and Cretaceous marine shale.Most of the source rocks have great capacity of gas generation.The source rocks can be summarized into four models.The main reservoir is the marine sandstone deposited in the rift stage,and the Cretaceous turbidites formed in the passive continental margin stage is a potential reservoir.The Lower Cretaceous marine shale is the main seal covering the whole region.From the view point of petroleum system,there are three reservoir-seal assemblages in the region including the marine reservoir-seal assemblage,paralic reservoir-seal assemblage and continental reservoir-seal assemblage,and the paralic reservoir-seal assemblage dominates.The major passes for hydrocarbon migration include structural ridges,faults,and unconformities.Overpressure,fault and unconformity are the major driving factors of hydrocarbon migration.In this study area major plays always occur in the lower sequence near the source with the upper parts as reservoir and seal.