Petroleum-rich basins at a mature stage of exploration and production offer many opportunities for large-scale Carbon Capture and Storage (CCS) since oil and gas were demonstrably contained by low-permeability top-sealing rocks, such as shales. For CCS to work, there must be effectively no leakage from the injection site, so the nature of the top-seal is an important aspect for consideration when appraising prospective CCS opportunities. The Lower Cretaceous Rodby Shale and the Palaeocene Lista Shale have acted as seals to oil and gas accumulations (e.g., the Atlantic and Balmoral fields) and may now play a critical role in sealing the Acorn and East Mey subsurface carbon storage sites. The characteristics of these important shales have been little addressed in the hydrocarbon extraction phase, with an understandable focus on reservoir properties and their influence on resource recovery rates. Here, we assess the characteristics of the Rodby and Lista Shales using wireline logs, geomechanical tests, special core analysis (mercury intrusion) and mineralogical and petrographic techniques, with the aim of highlighting key properties that identify them as suitable top-seals. The two shales, defined using the relative gamma log values (or Vshale), have similar mean pore throat radius (approximately 18 nm), splitting tensile strength (approximately 2.5 MPa) and anisotropic values of splitting tensile strength, but they display significant differences in terms of wireline log character, porosity and mineralogy. The Lower Cretaceous Rodby Shale has a mean porosity of approximately 14 %, a mean permeability of 263 nD (2.58 × 10⁻¹⁹ m²), and is calcite rich and has clay minerals that are relatively rich in non-radioactive phases such as kaolinite. The Palaeocene Lista Shale has a mean porosity of approximately 16% a mean permeability of 225 nD (2.21 × 10⁻¹⁹ m²), and is calcite free, but contains abundant quartz silt and is dominated by smectite. The 2% difference in porosity does not seem to equate to a significant difference in permeability. Elastic properties derived from wireline log data show that Young’s modulus, material stiffness, is very low (5 GPa) for the most shale (clay mineral)-rich Rodby intervals, with Young’s modulus increasing as shale content decreases and as cementation (e.g., calcite) increases. Our work has shown that Young’s modulus, which can be used to inform the likeliness of tensile failure, may be predictable based on routine gamma, density and compressive sonic logs in the majority of wells where the less common shear logs were not collected. The predictability of Young’s modulus from routine well log data could form a valuable element of CCS-site top-seal appraisals. This study has shown that the Rodby and Lista Shales represent good top-seals to the Acorn and East Mey CCS sites and they can hold CO₂ column heights of approximately 380 m. The calcite-rich Rodby Shale may be susceptible to localised carbonate dissolution and increasing porosity and permeability but decreasing tendency to develop fracture permeability in the presence of injected CO₂, as brittle calcite dissolves. In contrast, the calcite-free, locally quartz-rich, Lista Shale will be geochemically inert to injected CO₂ but retain its innate tendency to develop fracture permeability (where quartz rich) in the presence of injected CO₂.

中文翻译：

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下白垩统Rodby和古新世Lista页岩：英国近海两个计划中的CCS站点顶部密封泥岩的特征与比较

在石油勘探开发和生产的成熟阶段，富含石油的盆地为大规模的碳捕集与封存（CCS）提供了许多机会，因为石油和天然气被明确地包含在低渗透性的顶封岩石中，例如页岩。为了使CCS正常工作，注射部位必须没有泄漏，因此，在评估潜在CCS机会时，顶部密封的性质是要考虑的重要方面。下白垩纪的罗德比页岩和古新世李斯塔页岩已成为油气聚集（例如大西洋和巴尔莫拉尔油田）的密封层，现在可能在密封橡子和东梅伊地下碳储藏地点中发挥关键作用。这些重要页岩的特征在烃萃取阶段几乎未得到解决，可以理解的重点是储层特性及其对资源采收率的影响。在这里，我们使用电缆测井仪，地质力学测试，特殊岩心分析（汞侵入）以及矿物学和岩石学技术评估了罗德比和利斯塔页岩的特征，目的是突出表明将其识别为合适的上盖层的关键特性。使用相对伽马对数值（或Vshale）定义的两种页岩具有相似的平均孔喉半径（约18 nm），抗张强度（约2.5 MPa）和抗张强度的各向异性值，但它们在电缆测井特征，孔隙度和矿物学方面的术语。下白垩纪罗德比页岩的平均孔隙度约为14％，平均渗透率为263 nD（2.58×10 我们使用电缆测井，地质力学测试，特殊岩心分析（汞侵入）以及矿物学和岩石学技术评估了罗德比和利斯塔页岩的特征，目的是突出表明将其识别为合适的上封层的关键特性。使用相对伽马对数值（或Vshale）定义的两种页岩具有相似的平均孔喉半径（约18 nm），抗张强度（约2.5 MPa）和抗张强度的各向异性值，但它们在电缆测井特征，孔隙度和矿物学方面的术语。下白垩纪罗德比页岩的平均孔隙度约为14％，平均渗透率为263 nD（2.58×10 我们使用电缆测井，地质力学测试，特殊岩心分析（汞侵入）以及矿物学和岩石学技术评估了罗德比和利斯塔页岩的特征，目的是突出表明将其识别为合适的上封层的关键特性。使用相对伽马对数值（或Vshale）定义的两种页岩具有相似的平均孔喉半径（约18 nm），抗张强度（约2.5 MPa）和抗张强度的各向异性值，但它们在电缆测井特征，孔隙度和矿物学方面的术语。下白垩纪罗德比页岩的平均孔隙度约为14％，平均渗透率为263 nD（2.58×10 特殊的岩心分析（水银侵入）以及矿物学和岩石学技术，目的是突出突出关键特性，将其识别为合适的顶部密封件。使用相对伽马对数值（或Vshale）定义的两种页岩具有相似的平均孔喉半径（约18 nm），抗张强度（约2.5 MPa）和抗张强度的各向异性值，但它们在电缆测井特征，孔隙度和矿物学方面的术语。下白垩纪罗德比页岩的平均孔隙度约为14％，平均渗透率为263 nD（2.58×10 特殊的岩心分析（水银侵入）以及矿物学和岩石学技术，目的是突出突出关键特性，将其识别为合适的顶部密封件。使用相对伽马对数值（或Vshale）定义的两种页岩具有相似的平均孔喉半径（约18 nm），抗张强度（约2.5 MPa）和抗张强度的各向异性值，但它们在电缆测井特征，孔隙度和矿物学方面的术语。下白垩纪罗德比页岩的平均孔隙度约为14％，平均渗透率为263 nD（2.58×10 具有相似的平均孔喉半径（约18 nm），断裂抗张强度（约2.5 MPa）和断裂抗张强度的各向异性值，但在测井曲线，孔隙度和矿物学方面表现出显着差异。下白垩纪罗德比页岩的平均孔隙度约为14％，平均渗透率为263 nD（2.58×10 具有相似的平均孔喉半径（约18 nm），断裂抗张强度（约2.5 MPa）和断裂抗张强度的各向异性值，但在测井曲线，孔隙度和矿物学方面表现出显着差异。下白垩纪罗德比页岩的平均孔隙度约为14％，平均渗透率为263 nD（2.58×10^-19 m ²），方解石丰富，且粘土矿物中非放射性相（例如高岭石）相对丰富。古新世李斯塔页岩的平均孔隙度约为16％，平均渗透率为225 nD（2.21×10 ^-19 m ²），不含方解石，但含有丰富的石英粉砂，并且以蒙脱石为主。孔隙率2％的差异似乎并不等于渗透率的显着差异。从电缆测井数据得出的弹性性质表明，对于最富页岩（粘土矿物）的罗德井间隔，杨氏模量，材料刚度非常低（5 GPa），随着页岩含量减少和胶结作用（例如方解石），杨氏模量增加）增加。我们的工作表明，杨氏模量（可用于告知拉伸破坏的可能性）可以根据大多数未收集较不常见的剪切测井的常规伽马，密度和压缩声波测井来预测。根据常规测井数据对杨氏模量的可预测性可能构成CCS现场顶封评价的重要组成部分。_2个柱高约380 m。富含方解石的罗德比页岩可能易受局部碳酸盐溶解的影响，并增加孔隙度和渗透率，但由于脆性方解石溶解，在注入CO ₂的情况下降低了裂缝渗透率的趋势。相反，无方解石，局部富含石英的利斯塔页岩对注入的CO ₂具有地球化学惰性，但在注入的CO ₂存在的情况下仍保持其固有的发展裂缝渗透性的趋势（在富含石英的情况下）。