Abstract Micron-sized fluid inclusions within quartz grains from Late Cretaceous sandstones, recovered from drill cuttings from four wells in the Great Australian Bight, contain palaeo-fluids such as brine, black oil, light oil, gas condensate, and N2 and CO2-rich hydrocarbon gas, providing evidence of multiple palaeo-hydrocarbon migration in the Bight Basin. A series of microscopic, spectroscopic and thermometric characterisation techniques were applied to the petroleum fluid inclusions in Gnarlyknots-1A, Potoroo-1, Greenly-1 and Duntroon-1 in order to estimate fluid types, palaeo-pressures and palaeo-temperatures (PT) of hydrocarbon entrapment, and to provide constraints on the age of petroleum migration in the central and eastern parts of the Ceduna Sub-basin. The Coniacian interval (Tiger Supersequence) in Gnarlyknots-1A trapped a variety of petroleum fluid types (black oil, light oil and gas-condensate) over an extended period. The earliest phase of oil entrapment recorded in quartz grains took place at a minimum of 58 °C as light oil and, together with pressure, constraints this to the end of the Cretaceous (circa 75 Ma). Source rocks capable of light oil generation at this time occur in the Blue Whale Supersequence. Petroleum compositions evolved toward more gas-rich fluids during the Cenozoic. This, together with some late oil constrained to Miocene age migration, implies generation from at least two source rocks. Source rocks capable of generating gas at this time are interpreted to be in the Blue Whale and White Pointer supersequences, while late oil may have been expelled from the Tiger Supersequence in the central basin depocentre. The palaeo-PT evolution recorded by the fluid inclusions in Gnarlyknots-1A closely follows the modelled burial curve, suggesting that the petroleum fluids were in thermal equilibrium with the rock. In contrast, the oil and gas inclusion assemblages found at Potoroo-1, Greenly-1 and Duntroon-1 were trapped later, with some at temperatures higher than the formation temperatures predicted from burial models. Whilst there are several potential mechanisms that explain these observations, we suggest that these wells are located near major extensional faults that have the potential for conducting fluids upwards. Additionally, gases such as CO2 and N2 associated with hydrocarbons possibly relate to mixing with mantle-derived fluids, which may also have contributed to the aforementioned thermal anomalies.

中文翻译：

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约束海湾盆地油气运移的时间和演化

摘要 晚白垩世砂岩石英颗粒内的微米级流体包裹体，从大澳大利亚湾四口井的钻屑中回收，包含古流体，如盐水、黑油、轻油、凝析气以及富含 N2 和 CO2烃气，提供了湾湾盆地多次古烃运移的证据。为了估计流体类型、古压力和古温度 (PT)，对 Gnarlyknots-1A、Potoroo-1、Greenly-1 和 Duntroon-1 中的石油流体包裹体应用了一系列显微、光谱和测温表征技术烃圈闭，并限制塞杜纳盆地中部和东部的石油运移年龄。Gnarlyknots-1A 中的 Coniacian 层段（Tiger Supersequence）在很长一段时间内捕获了多种石油流体类型（黑油、轻油和凝析气）。记录在石英颗粒中的最早的油包封阶段发生在最低 58 °C 时，作为轻质油，加上压力，将其限制在白垩纪末期（大约 75 Ma）。此时能够产生轻质油的烃源岩出现在蓝鲸超层序中。在新生代，石油成分向富含气体的流体演化。这与一些受中新世时代迁移限制的晚期石油一起，意味着至少有两个烃源岩的生成。此时能产气的烃源岩被解释为蓝鲸和白指针超层序，而晚期石油可能是从中央盆地沉积中心的老虎超层序中排出的。Gnarlyknots-1A 中流体包裹体记录的古 PT 演化与模拟的埋藏曲线密切相关，表明石油流体与岩石处于热平衡。相比之下，在 Potoroo-1、Greenly-1 和 Duntroon-1 发现的油气包裹体组合较晚被捕获，其中一些温度高于埋藏模型预测的地层温度。虽然有几种可能的机制可以解释这些观察结果，但我们认为这些井位于有可能向上引导流体的主要伸展断层附近。此外，与碳氢化合物相关的 CO2 和 N2 等气体可能与地幔衍生流体的混合有关，