The Toolebuc Formation of Australia, a potential unconventional hydrocarbon resource, has limited studies on its pore structure and sorption characteristics. In this study, shale samples covering the lower mixed argillaceous mudstone (MAM) lithofacies, the middle interbedded calcareous mudstone and shelly thin beds (CM-STB) lithofacies, and the upper interbedded calcareous mudstone and shelly horizons (CM-SH) lithofacies of the Toolebuc Formation were collected. These samples were analysed for pore structure using a combination of scanning electron microscopy, X-ray diffraction, helium pycnometry, mercury intrusion porosimetry, and N physisorption techniques. Additionally, methane sorption isotherms were measured under in-situ conditions. The results reveal that most pores are mineral-related intraparticle (intraP) and interparticle pores, with slit, equant and elongated shapes. Organic matter (OM) pores are rare. Porosity, total pore volume and BET specific surface area (SSA) are 3.25–8.26%, 1.32–3.55 cm/100 g, and 1.26–9.65 m/g, respectively. Pore volume is dominated by mesopores and macropores while specific surface area is dominated by fine mesopores and micropores. The porosity of the organic matter is significantly low due to the rarity of OM pores in the stage of early oil-window thermal maturity; organic matter consequently occludes pore space and also negatively impacts the average porosity. Clay by contrast is positively correlated to the average porosity. Carbonate provides intraP pores in fecal pellets, but also fills in other pore spaces as occlusion. Methane isotherms exhibit linear shapes, suggesting that a portion of the gas is stored in solution. The lower MAM lithofacies, characterised by rich clay, high porosity and BET SSA, was measured to have an in-situ methane sorption capacity of 4.32 cm/g; the middle CM-STB lithofacies has intermediate porosity, but exhibits excellent gas generation potential and high in-situ methane sorption capacity (4.12–5.5 cm/g). Within the CM-STB lithofacies, porosity declines with depth. The upper CM-SH lithofacies is carbonate-rich, exhibiting the lowest porosity and in-situ methane sorption capacity (2.56 cm/g), but may act as an intraformational seal. The combination and vertical stacking pattern of the three lithofacies provided a favourable setting for gas storage.

中文翻译：

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Toolebuc 地层孔隙的起源和性质，澳大利亚潜在的非常规目标

澳大利亚Toolebuc组是一种潜在的非常规油气资源，对其孔隙结构和吸附特性的研究有限。在这项研究中，页岩样品覆盖了下层混合泥岩（MAM）岩相、中层互层钙质泥岩和贝壳薄层（CM-STB）岩相以及上层互层钙质泥岩和贝壳层（CM-SH）岩相。收集了 Toolebuc 地层。使用扫描电子显微镜、X射线衍射、氦比重测定法、压汞孔隙率测定法和N物理吸附技术的组合来分析这些样品的孔隙结构。此外，在原位条件下测量了甲烷吸附等温线。结果表明，大多数孔隙为与矿物相关的粒内孔和粒间孔，形状为狭缝状、等长状和细长状。有机质（OM）孔隙很少见。孔隙率、总孔体积和BET比表面积（SSA）分别为3.25-8.26%、1.32-3.55 cm/100 g和1.26-9.65 m/g。孔体积以介孔和大孔为主，比表面积以细介孔和微孔为主。早期油窗热成熟阶段，由于有机质孔隙稀少，有机质孔隙度明显较低；因此，有机物会堵塞孔隙空间，并对平均孔隙率产生负面影响。相比之下，粘土与平均孔隙度呈正相关。碳酸盐在粪便颗粒中提供了内部孔隙，但也填充了其他孔隙空间作为闭塞物。甲烷等温线呈现线性形状，表明一部分气体储存在溶液中。下MAM岩相以富粘土、高孔隙度和BET SSA为特征，测得原位甲烷吸附能力为4.32 cm/g；中CM-STB岩相具有中等孔隙度，但具有良好的产气潜力和较高的原位甲烷吸附能力（4.12~5.5 cm/g）。在 CM-STB 岩相中，孔隙度随深度而降低。上部 CM-SH 岩相富含碳酸盐，表现出最低的孔隙度和原位甲烷吸附能力（2.56 cm/g），但可能充当地层内封闭。三种岩相的组合和垂直叠置格局为储气提供了有利的环境。