Origin and nature of pores in the Toolebuc Formation, a potential unconventional target in Australia

IF 5.6 2区 工程技术 Q2 ENERGY & FUELS
Xiaoxiao Mao , Grant K.W. Dawson , Victor Rudolph , Sandra Rodrigues , Suzanne D. Golding
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引用次数: 0

Abstract

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 N2 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 cm3/100 g, and 1.26–9.65 m2/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 cm3/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 cm3/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 cm3/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.

澳大利亚潜在的非常规目标--托勒布克地层孔隙的起源和性质
澳大利亚图勒布克地层是一种潜在的非常规碳氢化合物资源,但对其孔隙结构和吸附特征的研究却很有限。在这项研究中,采集了页岩样本,涵盖了 Toolebuc Formation 的下部混合砾质泥岩(MAM)岩性、中部互层钙质泥岩和薄层钙质泥岩(CM-STB)岩性以及上部互层钙质泥岩和钙质地层(CM-SH)岩性。采用扫描电子显微镜、X 射线衍射、氦气比重测定法、汞侵入孔隙测定法和 N2 物理吸附技术对这些样本的孔隙结构进行了分析。此外,还在原位条件下测量了甲烷吸附等温线。结果表明,大多数孔隙是与矿物有关的颗粒内(intraP)和颗粒间孔隙,形状有狭缝形、等长形和拉长形。有机物(OM)孔隙很少见。孔隙率、总孔隙体积和 BET 比表面积(SSA)分别为 3.25%-8.26%、1.32-3.55 立方厘米/100 克和 1.26-9.65 平方米/克。孔隙体积主要是中孔和大孔,而比表面积主要是细中孔和微孔。在早期油窗热成熟阶段,由于有机质孔隙稀少,有机质的孔隙率明显偏低;有机质因此堵塞了孔隙空间,也对平均孔隙率产生了负面影响。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 P 内孔隙,但也作为闭塞物填充了其他孔隙空间。甲烷等温线呈现线性形状,表明部分气体储存在溶液中。下层 MAM 岩性的特点是富粘土、高孔隙度和 BET SSA,经测量,其甲烷原位吸附能力为 4.32 立方厘米/克;中层 CM-STB 岩性的孔隙度居中,但表现出良好的气体生成潜力和较高的甲烷原位吸附能力(4.12-5.5 立方厘米/克)。在 CM-STB 岩性中,孔隙度随深度下降。上部的 CM-SH 岩性富含碳酸盐,孔隙度和原位甲烷吸附能力最低(2.56 立方厘米/克),但可能起到地层内部封闭的作用。三种岩性的组合和垂直堆积模式为天然气储存提供了有利条件。
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来源期刊
International Journal of Coal Geology
International Journal of Coal Geology 工程技术-地球科学综合
CiteScore
11.00
自引率
14.30%
发文量
145
审稿时长
38 days
期刊介绍: The International Journal of Coal Geology deals with fundamental and applied aspects of the geology and petrology of coal, oil/gas source rocks and shale gas resources. The journal aims to advance the exploration, exploitation and utilization of these resources, and to stimulate environmental awareness as well as advancement of engineering for effective resource management.
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