Deformation Experiments on Bowland and Posidonia ShalePart I: Strength and Young's Modulus at Ambient and In Situ pc-T Conditions
Deformation Experiments on Bowland and Posidonia ShalePart I: Strength and Young's Modulus at Ambient and In Situ pc-T Conditions
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DOI：
10.1007/s00603-018-1572-4
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发表时间：
2018-12-01
影响因子：
6.2
通讯作者：
Dresen, G.
中科院分区：
文献类型：
--
作者：
Herrmann, J.;Rybacki, E.;Dresen, G.
过去十年，来自致密页岩等非常规储集层的碳氢化合物产量大幅增加。水力压裂是提高这些油气藏钻井产能的常用方法。不幸的是，随着时间的推移，产量会下降，这可能是由于裂缝闭合。支撑剂破碎和埋入引起的裂缝闭合率取决于页岩和支撑剂的力学性能，而页岩和支撑剂的力学性能受围压(p(C))、温度(T)和页岩成分的影响。我们使用不同矿物学、孔隙度和成熟度的欧洲页岩样品，在环境和现场条件下对一个典型的页岩储层(p(C)100 Mpa，T125℃)进行了恒应变速率变形测试。我们重点比较了波西多尼亚页岩和鲍兰页岩，后者被认为是英国最有前景的页岩地层。压缩试验垂直于层理方向进行。应力-应变曲线表明，鲍兰页岩表现出较强的脆性，而波西多尼亚页岩表现出半脆性变形特征。从弹性性质估算的脆性与记录的应力-应变行为很好地吻合，但与成分没有明显的关系。抗压强度(Sigma(Ics)=单轴抗压强度，Sigma(TCS)=三轴抗压强度)和静态杨氏模数E显示出很强的围压和矿物学依赖性，而温度和应变速率对Sigma(TCS)和E的影响很小。两个页岩的内耗系数约为0.42+/-0.03。随着弱矿物(如粘土、云母)含量的增加，西格玛(UCS)、西格玛(TCS)和E显著降低。这可能与由坚硬矿物的承重骨架支撑的变形转变为相互关联的弱矿物在约25-30vol%的弱相中变形有关。在应用条件下，垂直于层理变形的大多数页岩的三轴抗压强度和杨氏模数都接近Reuss界。据我们所知，这是第一项研究，介绍了为表征鲍兰页岩的力学行为而进行的实验研究结果。观测结果有助于估计鲍兰水库在经济开采碳氢化合物方面的潜力。
The production of hydrocarbons from unconventional reservoirs, like tight shale plays, increased tremendously over the past decade. Hydraulic fracturing is a commonly applied method to increase the productivity of a well drilled in these reservoirs. Unfortunately, the production rate decreases over time presumably due to fracture closure. The fracture closure rate induced by proppant crushing and embedment depends on mechanical properties of shales and proppants that are influenced by confining pressure (p(c)), temperature (T), and shale composition. We performed constant strain rate deformation tests at ambient and in situ conditions of a typical shale reservoir (p(c)100MPa, T125 degrees C) using European shale samples exhibiting variable mineralogy, porosity and maturity. We focused on a comparison of Posidonia shale with Bowland shale, which is believed to be the most prospective shale formation in the United Kingdom. Compression tests were performed perpendicular to bedding orientation. Stress-strain curves show that Bowland shales are relatively strong and brittle compared to Posidonia shale which display semibrittle deformation behavior. Brittleness estimated from elastic properties is in good agreement with the recorded stress-strain behavior but shows no clear relation to composition. Compressive strengths (sigma(UCS)=uniaxial compressive strength, sigma(TCS)=triaxial compressive strength) and static Young's moduli, E, reveal a strong confining pressure and mineralogy dependence, whereas temperature and strain rate only have a minor influence on sigma(TCS) and E. The coefficient of internal friction for both shales is approximate to 0.42 +/- 0.03. With increasing amount of weak minerals (e.g., clay, mica) sigma(UCS), sigma(TCS) and E strongly decrease. This may be related to a shift from deformation supported by a load-bearing framework of hard minerals to deformation of interconnected weak minerals at about 25-30vol% of weak phases. At the applied conditions, the triaxial compressive strength and Young's moduli of most shales deformed normal to bedding are close to the Reuss bound. To our knowledge, this is the first study, which presents results of experimental investigations carried out to characterize the mechanical behavior of Bowland shale. The observed results are helpful to estimate the potential of the Bowland reservoir with respect to the economical extraction of hydrocarbons.