Geomechanics for Energy and the Environment最新文献_第6页

Thermomechanical response and crack evolution of sandstone at elevated temperatures 砂岩在高温下的热力学响应和裂纹演变

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2024-10-05 DOI: 10.1016/j.gete.2024.100603

Amulya Ratna Roul , Vikram Vishal

Understanding the thermomechanical response of rock at high temperatures is crucial for various energy applications such as underground coal gasification and geothermal systems. The study investigated the effects of temperature, mineral composition, and grain size on crack initiation (CI) and crack damage (CD) thresholds in Jodhpur sandstones using uniaxial compressive strength with acoustic emission, Brazilian tensile strength, and thermogravimetric analysis subjected to elevated temperatures. The study revealed distinct patterns in crack initiation stress threshold ratios (CISTR) and crack damage stress threshold ratios (CDSTR) influenced by mineral composition and grain size under temperature treatments. Ferruginous quartz arenite exhibited an inverse relationship between quartz content and crack initiation/damage stress thresholds, while siliceous quartz arenite and subarkose showed a positive correlation. The established variation is attributed to the differing grain boundary strengths among the minerals. Comparative analysis of crack thresholds with the minerals, excluding quartz and feldspar, revealed complex relationships with clay and other minerals. Finer-grained sandstones showed direct proportionality in CI and CISTR with clay content, while coarser sandstones exhibited an inverse relationship. Additionally, the study highlighted differential trends in toughness parameters and CISTR, emphasizing the role of grain size and heat-treatment conditions in governing stress thresholds. Significant chemical changes, including quartz phase shifts and kaolinite/muscovite dehydroxylation, occurred in sandstones at 500–600°C. The presence of kaolinite/hematite in ferruginous quartz arenite caused the increased mass loss in pure O₂ due to kaolinite breakdown, while siliceous quartz arenite exhibited a greater mass loss in standard conditions. The findings suggest that quartz content does not consistently enhance rock strength under heat treatment, particularly in the presence of significant clay minerals, leading to an inverse quartz-rock strength relationship in ferruginous quartz arenites. The study provides valuable insights into the thermomechanical behavior of sandstones, which is crucial for assessing rock stability and durability in energy applications.

了解岩石在高温下的热力学响应对于地下煤炭气化和地热系统等各种能源应用至关重要。该研究利用声发射单轴抗压强度、巴西抗拉强度和高温下的热重分析，研究了温度、矿物成分和晶粒大小对焦特布尔砂岩裂纹起始（CI）和裂纹损伤（CD）阈值的影响。研究发现，在温度处理条件下，裂纹起始应力阈值比（CISTR）和裂纹损伤应力阈值比（CDSTR）受矿物成分和晶粒大小的影响模式截然不同。铁锈色石英砺石的石英含量与裂纹起始/破坏应力阈值之间呈反比关系，而硅质石英砺石和钠长石则呈正比关系。已确定的差异归因于矿物之间不同的晶界强度。除石英和长石外，裂缝阈值与矿物的比较分析表明，裂缝阈值与粘土和其他矿物之间存在复杂的关系。细粒度砂岩的 CI 和 CISTR 与粘土含量成正比，而粗粒度砂岩则成反比。此外，研究还突出了韧性参数和 CISTR 的不同趋势，强调了晶粒大小和热处理条件在控制应力阈值方面的作用。在 500-600°C 的温度下，砂岩发生了显著的化学变化，包括石英相变和高岭石/黑云母脱羟基。铁闪闪石英褐铁矿中高岭石/红柱石的存在导致高岭石分解引起的纯氧气质量损失增加，而硅质石英褐铁矿在标准条件下的质量损失更大。研究结果表明，在热处理条件下，石英含量并不能持续提高岩石强度，尤其是在存在大量粘土矿物的情况下，这导致铁纹石英质 arenite 中的石英-岩石强度呈反比关系。该研究为了解砂岩的热力学行为提供了宝贵的见解，这对于评估能源应用中岩石的稳定性和耐久性至关重要。

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引用次数: 0

Quantification of energy consumed in simulated percussive drilling process using dynamic indentation experiment 利用动态压痕实验量化模拟冲击钻孔过程中消耗的能量

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2024-10-05 DOI: 10.1016/j.gete.2024.100604

Wei Yao , Xuan Li , Guilherme Corrêa Soares , Mikko Hokka

The high cost of drilling deep wells is the main barrier to the widespread exploitation of deep geothermal energy. Percussive drilling is one of the significant drilling technologies used in energy exploration projects. However, there is no good quantitative understanding of how much energy in percussive drilling is consumed in pulverization, heating, the kinetic energy of particles, acoustic emission, etc. In this study, energy efficiency is quantitatively investigated to understand the percussive drilling process better. The dynamic percussive drilling was evaluated using a modified split Hopkinson pressure bar (SHPB) system and non-contact measurements. The amount of energy dissipated in different processes and the overall energy efficiency was estimated for Kuru granite, Balmoral granite, and Kivijärvi gabbro. The energy spent on the kinetic energy E_k of fragments was evaluated using a high-speed camera, whereas the energy consumed on heat or the thermal energy E_t was obtained by high-speed infrared imaging. The cracking energy E_c was measured by using the surface energy of rock and the total newly created surface areas. The results indicate that the fragment size distribution of these three rocks generally varies with the penetration speed, and the fragmentation level of these rocks increases with the penetration speed. The input energy and the energy consumption grow with the increase of the penetration speed. The proportions of E_t, E_k, and E_c in the total energy consumption for these three rocks increase with the penetration speed. The energy efficiency obtained from the dynamic indentation experiments for the three rocks generally increases with the penetration speed and almost approaches a limit value when the penetration speed is high. A model is improved to describe the relationship between energy efficiency and penetration speed quantitatively. Therefore, the penetration process should be optimized to balance the high drilling efficiency and the low energy consumption.

钻探深井的高昂成本是广泛开发深层地热能源的主要障碍。冲击钻井是能源勘探项目中使用的重要钻井技术之一。然而，对于冲击钻在粉碎、加热、颗粒动能、声发射等方面消耗了多少能量，目前还没有很好的定量了解。本研究对能效进行了定量研究，以更好地了解冲击钻的钻进过程。使用改进的分体式霍普金森压力棒（SHPB）系统和非接触式测量方法对动态冲击钻进进行了评估。估算了库鲁花岗岩、巴尔莫勒尔花岗岩和基维耶尔维辉长岩在不同过程中耗散的能量以及总体能量效率。使用高速照相机评估了碎片动能 Ek 消耗的能量，而热量或热能 Et 消耗的能量则是通过高速红外成像获得的。裂解能 Ec 是通过岩石表面能和新产生的总表面积来测量的。结果表明，这三种岩石的碎裂尺寸分布一般随穿透速度而变化，岩石的碎裂程度随穿透速度而增加。输入能量和能量消耗随着穿透速度的增加而增加。在这三种岩石的总能耗中，Et、Ek 和 Ec 所占的比例随着穿透速度的增加而增加。这三种岩石的动态压入实验所获得的能量效率一般随穿透速度的增加而增加，当穿透速度较高时，能量效率几乎接近极限值。改进的模型可以定量描述能量效率与贯入速度之间的关系。因此，应优化贯入过程，以兼顾高钻进效率和低能耗。

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引用次数: 0

Experimental investigation into the effect of porosity on the strains developing during anhydrite to gypsum transformation 关于孔隙率对无水石膏转化过程中产生的应变的影响的实验研究

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2024-09-27 DOI: 10.1016/j.gete.2024.100601

Antonia Nousiou, Erich Pimentel, Georgios Anagnostou

The swelling of anhydritic claystones often leads to severe tunnel damage. Even though this phenomenon has gained significant scientific interest, particularly in the last decades, there are still open questions which introduce uncertainties in tunnel design. One question concerns the strains developing during the anhydrite to gypsum transformation (AGT). These depend, among other factors, on whether the gypsum crystals grow within the available pore space or whether they tend to push the particles apart, leading to an expansion of the matrix and, in turn, larger macroscopic strains. The experimental investigations of this paper aim to assess the influence of the initial porosity on the strains developing during AGT. Specimens consisting of highly compacted anhydrite and kaolin powders are created with varying initial porosities between 0.22 and 0.35. It is concluded that, ceteris paribus, the strains developing during AGT decreases with increasing initial porosity. The results also indicate that in the case of high initial porosity the gypsum crystals grow in the available pore space, thus decreasing the porosity, while in the case of low initial porosity, gypsum growth leads to an increase of the pore space. The results are applicable to porous media where crystallisation may occur within the pores.

无水粘土岩的膨胀往往会导致隧道的严重破坏。尽管这一现象已经引起了科学界的极大兴趣，尤其是在过去的几十年中，但仍有一些悬而未决的问题，给隧道设计带来了不确定性。其中一个问题涉及无水石膏转化（AGT）过程中产生的应变。除其他因素外，这些应变取决于石膏晶体是在可用的孔隙空间内生长，还是倾向于将颗粒推开，从而导致基体膨胀，进而产生更大的宏观应变。本文的实验研究旨在评估初始孔隙率对 AGT 过程中产生的应变的影响。试样由高度压实的无水石膏和高岭土粉末组成，初始孔隙率在 0.22 和 0.35 之间。得出的结论是，在相同情况下，AGT 过程中产生的应变会随着初始孔隙率的增加而减小。结果还表明，在初始孔隙率较高的情况下，石膏晶体会在可用的孔隙空间中生长，从而降低孔隙率，而在初始孔隙率较低的情况下，石膏的生长会导致孔隙空间的增加。这些结果适用于可能在孔隙内发生结晶的多孔介质。

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引用次数: 0

Geothermal bridge deck de-icing using a novel external hydronic heating system with insulated pipe loops 使用带保温管环路的新型外部水力加热系统进行地热桥面除冰

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2024-09-27 DOI: 10.1016/j.gete.2024.100602

Omid Habibzadeh-Bigdarvish , Gang Lei , Hussein Hashemi Senejani , Alireza Fakhrabadi , Anand J. Puppala , Xinbao Yu

A geothermal-based external hydronic heating system (EHHS) has been developed as an effective solution to address the de-icing needs of in-service bridges with minimum negative impacts on the structure, traffic, and environment. This paper discusses the implementation and operational response of a new design of the EHHS in which rather than the whole bottom surface of the bridge deck, only the hydronic heating loops are covered with insulation material and provides the accessibility for visual inspection of the bridge deck. The first full-scale external hydronic heating system with an insulated loop (EHHS-IL) was installed on a mock-up bridge deck in north Texas and tested in a record snowstorm with a low ambient temperature of −19.5 ˚C. The system operated in three different stages, and the inlet fluid temperature was adjusted according to the weather forecast. Overall, during a 10-day operation, three ice and snow events and 209 hours of freezing ambient temperature were observed. The heating system was able to maintain the heated bridge deck surface temperature above freezing except for 1.3 hours when the −19.5 ˚C low ambient temperature coincided with snowfall. The average surface heat flux during the test varied from 34.8 – 84 W/m^2, and the average heating efficiency was estimated at 17.7 %. The seasonal performance factor (SPF) of the system remains consistently greater than 1 during the heating period. Also, 422 kWh of electrical energy was consumed during 10 days of operation by the entire geothermal de-icing system. This new geothermal bridge deicing system offers a practical solution to icy bridges by retrofitting.

以地热为基础的外部水力加热系统（EHHS）是解决在役桥梁除冰需求的有效解决方案，对结构、交通和环境的负面影响最小。本文讨论了 EHHS 新设计的实施和运行反应，在该设计中，仅在水力加热环路上覆盖隔热材料，而不是整个桥面的底面，并为桥面的可视检查提供了便利。第一个带隔热环路的全尺寸外部水力加热系统（EHHS-IL）安装在德克萨斯州北部的一个模拟桥面上，并在创纪录的暴风雪中进行了测试，环境温度低至零下 19.5 ˚C。系统分三个不同阶段运行，入口流体温度根据天气预报进行调整。总体而言，在为期 10 天的运行期间，共观测到三次冰雪天气和 209 小时的冰冻环境温度。除 1.3 小时内因降雪而出现-19.5 ˚C的低环境温度外，加热系统能够将加热后的桥面表面温度保持在冰点以上。测试期间的平均表面热通量在 34.8 - 84 W/m2 之间变化，平均加热效率估计为 17.7%。在供暖期间，系统的季节性能系数（SPF）始终大于 1。此外，整个地热除冰系统在 10 天的运行期间消耗了 422 千瓦时的电能。这种新型地热桥梁除冰系统通过改造为结冰桥梁提供了一种实用的解决方案。

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引用次数: 0

Vertical dynamic responses of model energy piles 模型能量桩的垂直动态响应

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2024-09-25 DOI: 10.1016/j.gete.2024.100598

Lingfei Su , Chenglong Wang , Abdelmalek Bouazza , Gangqiang Kong , Xuanming Ding

This paper explores the dynamic responses of model energy piles embedded in sand subjected to the combined effects of temperature change and cyclic mechanical loading. The same type of cyclic loading was applied separately on three single energy piles with temperature differences (ΔT) of −20 ℃, +20 ℃ and 0 ℃, respectively. The results show that after 2000 cycles of mechanical loading, the cumulative displacement of the energy pile increased under cooling conditions and decreased under heating conditions. The tip resistance of a single energy pile increased under both conditions, especially during cooling.

本文探讨了嵌入砂中的模型能量桩在温度变化和循环机械荷载的共同作用下的动态响应。对温差（ΔT）分别为-20 ℃、+20 ℃和0 ℃的三个单个能量桩分别施加了相同类型的循环荷载。结果表明，在机械加载 2000 个循环后，能量桩的累积位移在冷却条件下增加，在加热条件下减少。在这两种条件下，单根能量桩的桩尖阻力都有所增加，尤其是在冷却条件下。

引用次数: 0

Shear-induced fluid localization, episodic fluid release and porosity wave in deformable low-permeability rock salt 可变形低渗透性岩盐中剪切诱导的流体定位、偶发性流体释放和孔隙度波

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2024-09-21 DOI: 10.1016/j.gete.2024.100600

Yifeng Wang , Hua Shao , Kristopher L. Kuhlman , Carlos F. Jove-Colon , Olaf Kolditz

Understanding fluid distribution and migration in deformable low-permeability rock salt is critical for geologic disposal of nuclear waste. Field observations indicate that fluids in a salt formation are likely compartmentalized into relatively isolated patches and fluid release from such a formation is generally episodic. The underlying mechanism for these phenomena remains poorly understood. In this paper, a hydrological-mechanical model is formulated for fluid percolation in a rock salt formation under a deviatoric stress. Using a linear stability analysis, we show that a porosity wave (a train of alternating high and low porosity pockets) can emerge from positive feedbacks among intergranular wetting, grain boundary weakening and shear-induced material dilatancy. Fluid localization or episodic release can be viewed as a stationary or propagating porosity wave respectively. Fluid pockets transported via a porosity wave remain relatively isolated with minimal mixing between neighboring pockets. We further show that the velocity of fluid flow can be significantly enhanced by the emergence of a porosity wave. The concept and the related model presented in this paper provide a unified consistent explanation for the key features observed in fluid flow in rock salt. The similar process is expected to occur in other deformable low-permeability media such as shale and partially molten rocks under a deviatoric stress. Thus, the result presented here has an important implication to hydrocarbon expulsion from shale source rocks, radioactive waste isolation in a tight rock repository, and caprock integrity of a subsurface gas (CO₂, H₂ or CH₄) storage system. It may also help develop a new engineering approach to fluid injection into or extraction from unconventional reservoirs.

了解可变形低渗透岩盐中的流体分布和迁移对于核废料的地质处置至关重要。实地观察表明，盐层中的流体很可能被分隔成相对孤立的小块，从这种盐层中释放出来的流体通常是偶发性的。人们对这些现象的基本机制仍然知之甚少。本文针对偏差应力作用下岩盐地层中的流体渗流建立了一个水文力学模型。通过线性稳定性分析，我们发现，晶间润湿、晶界弱化和剪切引起的材料膨胀之间的正反馈会产生孔隙度波（一连串交替出现的高孔隙度和低孔隙度袋）。流体的局部或偶发释放可分别视为静止或传播的孔隙度波。通过孔隙波传输的流体袋保持相对孤立，相邻流体袋之间的混合极少。我们进一步证明，多孔波的出现可以显著提高流体的流动速度。本文提出的概念和相关模型为岩盐中流体流动的主要特征提供了统一一致的解释。类似的过程预计也会发生在其他可变形的低渗透介质中，如偏离应力作用下的页岩和部分熔融岩。因此，本文介绍的结果对页岩源岩中碳氢化合物的排出、致密岩储存库中放射性废物的隔离以及地下气体（CO2、H2 或 CH4）储存系统的盖岩完整性具有重要意义。它还有助于开发一种新的工程方法，将流体注入非常规储层或从非常规储层中提取流体。

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引用次数: 0

Assessing swelling-induced damage in shale samples during triaxial testing 在三轴测试过程中评估页岩样本中膨胀引起的损伤

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2024-09-20 DOI: 10.1016/j.gete.2024.100599

E. Crisci , R. Ewy , A. Ferrari , S.B. Giger

In shale testing, understanding the impact of effective stress and saturation conditions is crucial for accurate material behaviour assessment and parameter determination. In some cases, saturation in triaxial testing starts at low effective stress before ramping up for shearing. However, when in contact with water (or saline water), shales are prone to swelling, particularly at low effective stress levels, which can induce fissures and alter material properties. This study investigates the influence of fluid saturation strategies and stress/pressure variations on the mechanical behaviour of shales, particularly under low effective confinement. Building upon the comprehensive testing campaign (>140 tests) in Crisci et al. (2024), additional tests were conducted on Opalinus Clay shale, focusing on sample saturation methods and loading histories before shearing. The conditions under which tested specimens experience damage were detected through diagnostic indicators such as differences in stress path and lower strength and stiffness compared to intact specimens with identical basic properties. Micro CT scanning confirms that damage is related to the development of fissures. The volumetric changes in specimens were quantified throughout the testing phases and thresholds for tolerable strains and effective stresses, specific to this material, were established. Comparative analysis with Opalinus Clay from shallower depths and other shales globally revealed consistent findings. Notably, it is shown that, for all shale types analyzed, a linear failure envelope emerges in the low to intermediate effective stress regime when filtering out "damaged" specimens. This suggests that non-linear failure envelopes observed in some cases may stem from exposing specimens to low effective stress before shearing.

在页岩测试中，了解有效应力和饱和条件的影响对于准确评估材料性能和确定参数至关重要。在某些情况下，三轴测试中的饱和始于较低的有效应力，然后才逐渐升高进行剪切。然而，当页岩与水（或盐水）接触时，很容易发生膨胀，尤其是在低有效应力水平下，这会诱发裂缝并改变材料特性。本研究调查了流体饱和策略和应力/压力变化对页岩机械行为的影响，尤其是在低有效约束条件下。在 Crisci 等人（2024 年）的综合测试活动（140 次测试）的基础上，对 Opalinus Clay 页岩进行了额外的测试，重点是样品饱和方法和剪切前的加载历史。通过诊断指标，如与基本属性相同的完好试样相比，应力路径的差异以及强度和刚度的降低，检测出测试试样出现损坏的条件。显微 CT 扫描证实，损坏与裂缝的发展有关。在整个测试阶段，对试样的体积变化进行了量化，并确定了这种材料特有的可容忍应变和有效应力阈值。与较浅深度的 Opalinus Clay 和全球其他页岩的对比分析显示了一致的结果。值得注意的是，对于所分析的所有页岩类型，在过滤掉 "受损 "试样后，在中低有效应力范围内会出现线性破坏包络。这表明，在某些情况下观察到的非线性破坏包络可能是由于试样在剪切前暴露在低有效应力下造成的。

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引用次数: 0

A numerical analysis of Thermo–Hydro–Mechanical behavior in the FE experiment at Mont Terri URL: Investigating capillary effects in bentonite on the disposal system 对 Mont Terri URL 的 FE 实验中的热-水-机械行为进行数值分析：调查膨润土中的毛细管效应对弃置系统的影响

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2024-09-19 DOI: 10.1016/j.gete.2024.100597

Taehyun Kim , Chan-Hee Park , Changsoo Lee , Jin-Seop Kim , Eui-Seob Park , Bastian Graupner

We investigated thermo–hydro–mechanical (T-H–M) coupled behavior observed during the full-scale heater emplacement experiment at the Mont-Terri underground research laboratory conducted in the Opalinus clay as part of the DECOVALEX-2023 Task C project. Utilizing the OGS-FLAC simulator, we created a three-dimensional model to simulate multiphase flow in the experiment, applying extended Philip and de Vries’ model and incorporating the anisotropic T–H–M properties of the Opalinus clay. The simulation, which included a ventilation process, spanned five years of heating experiments and successfully replicated the measured temperature, pore pressure, displacement, and relative humidity results in bentonite and host rock during the experiment. The analysis revealed that capillary pressure significantly influenced the pore pressure change in the host rock near the tunnel, while thermal pressurization became dominant with increasing distance. Consequently, we conducted a sensitivity analysis on a simplified model to evaluate the effect of capillary pressure on the disposal system. Capillarity is a dominant factor for the multiphase flow depending on the distance from the heat. Variations in capillary pressure were observed depending on the gas entry pressure and water retention model, indicating that the capillarity of unsaturated bentonite could inherently affect the T–H–M results within the disposal system.

作为 DECOVALEX-2023 任务 C 项目的一部分，我们研究了在 Mont-Terri 地下研究实验室的 Opalinus 粘土中进行的全面加热器置入实验中观察到的热-水-机械（T-H-M）耦合行为。利用 OGS-FLAC 模拟器，我们创建了一个三维模型来模拟实验中的多相流，应用了 Philip 和 de Vries 的扩展模型，并结合了 Opalinus 粘土的各向异性 T-H-M 特性。该模拟包括一个通风过程，跨越了五年的加热实验，成功地复制了实验期间在膨润土和主岩中测量到的温度、孔隙压力、位移和相对湿度结果。分析表明，毛细管压力对隧道附近主岩的孔隙压力变化有显著影响，而随着距离的增加，热加压成为主要影响因素。因此，我们对简化模型进行了敏感性分析，以评估毛细管压力对弃置系统的影响。毛细管是多相流的主导因素，取决于与热量的距离。毛细管压力的变化取决于气体进入压力和保水性模型，这表明非饱和膨润土的毛细管性可能会在本质上影响处理系统内的 T-H-M 结果。

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引用次数: 0

Numerical investigation of the thermal hydrofracturing behavior of the Callovo-Oxfordian claystone 卡勒沃-牛津粘土岩热压破裂行为的数值研究

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2024-09-15 DOI: 10.1016/j.gete.2024.100596

Carlos Plúa , Minh-Ngoc Vu , Gilles Armand , Zady Ouraga , Zhan Yu , Jian-Fu Shao , Qianyun Wang , Hua Shao , Tsubasa Sasaki , Sangcheol Yoon , Jonny Rutqvist , Fei Song , Stefano Collico , Antonio Gens , Louise Bruffell , Kate Thatcher , Alexander E. Bond

This study addresses the thermal hydrofracturing behavior in claystone within the context of the high-level and intermediate-level long-lived radioactive waste disposal. The heat generated by the waste packages will lead to a temperature increment within the host formation, inducing a pore pressure build-up essentially due to the difference between the thermal expansion coefficient of the pore water and that of the solid skeleton. If the induced pore pressure build-up is too high, the host formation will experience tensile stresses, potentially exceeding its tensile strength and resulting in fracturing. Understanding of these processes and improving numerical models to reproduce them will help the design, optimization, and safety of the repository. Additionally, it will contribute to demonstrating robustness by showing that such processes are not expected to occur at the repository scale.

This study was conducted as part of the DECOVALEX-2023 project and synthesizes the efforts of six research teams modelling laboratory thermal extension tests conducted on Callovo-Oxfordian claystone (COx) samples, as well as an in-situ thermal hydrofracturing experiment conducted at the Meuse/Haute-Marne Underground Research Laboratory in France. The teams used different numerical codes with different approaches, including continuum and discrete approaches, to model these two tests. The laboratory tests were used to calibrate the teams’ models, such as the fracturing criterion. The teams considered a thermo-hydromechanical formulation under saturated conditions. One of the key features of their models was the incorporation of changes in the hydraulic properties of the COx through hydromechanical coupling.

The approaches developed by the teams demonstrated their capability to analyze and reproduce fracture initiation in the COx in terms of time of occurrence and location based on their respective stress analyses. However, attempts to reproduce fracture aperture or fracture propagation were less accurate and remain areas for future research, which were beyond the scope of this study.

本研究以高水平和中水平长寿命放射性废物处置为背景，探讨粘土岩的热压裂行为。废物包产生的热量会导致主地层内的温度升高，从而引起孔隙压力增大，这主要是由于孔隙水的热膨胀系数与固体骨架的热膨胀系数之间存在差异。如果诱导的孔隙压力积聚过高，主地层将承受拉伸应力，有可能超过其抗拉强度，导致断裂。了解这些过程并改进数字模型以再现这些过程，将有助于设计、优化和保证储存库的安全。本研究是 DECOVALEX-2023 项目的一部分，综合了六个研究团队的工作成果，包括对 Callovo-Oxfordian 粘土岩（COx）样本进行的实验室热延伸试验建模，以及在法国 Meuse/Haute-Marne 地下研究实验室进行的原位热压裂实验。研究小组使用不同的数值代码和不同的方法（包括连续和离散方法）对这两项试验进行建模。实验室测试用于校准团队的模型，如压裂标准。研究小组考虑了饱和条件下的热-水-力学模型。各小组开发的方法表明，他们有能力根据各自的应力分析，在发生时间和位置方面分析和再现 COx 的断裂起始。然而，再现断裂孔径或断裂扩展的尝试不太准确，仍是未来研究的领域，超出了本研究的范围。

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引用次数: 0

A complete experimental study on hard granites: Microstructural characterization, mechanical response, and failure criterion 关于硬质花岗岩的完整实验研究：微结构表征、机械响应和破坏标准

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2024-09-11 DOI: 10.1016/j.gete.2024.100592

Stéphane Dumoulin , Isabelle Thenevin , Alexandre Kane , Ahmed Rouabhi , John-Paul Latham , Emad Jahangir , Hedi Sellami

This study, performed during the ORCHYD European project, devoted to drilling deep geothermal boreholes, has many potential applications to mechanical studies. It gathers geological descriptions of three outcropping granites from Scandinavia (Kuru Grey and Red Bohus) and from the South of France (Sidobre). Microstructural investigations include optical microscopy and X-ray tomography. The three granites chosen contain grain sizes that cover all the common ranges for granites: fine, medium and coarse. As the mineral phase volume fractions are similar in each, the grain defects and grain boundaries are carefully studied in an attempt to understand the physical and mechanical properties of the three granite rock samples measured at laboratory specimen scale. The rocks are tested for UCS, BTS and triaxial compressive strength with confining pressures up to 225 MPa or/and high strain-rates up to 10³/s. The micro-structural parameters influencing the mechanical behaviour are highlighted. Test results show that the effect of confining pressure and strain-rate on compressive strength are uncoupled. These effects are then estimated independently, and a fracture criterion in compression accounting for both variables is proposed for the family of very hard granites. This criterion takes as a single reference strength measure for each rock the deviatoric stress at failure under 20 MPa confining stress in the quasi-static regime. It is then compared with existing datasets for which both quasi-static and dynamic regime data are available. This complete data set on these three very hard granites (UCS ∼ 200 MPa), together with a synthesis for failure prediction, has the potential to inform numerous rock engineering projects and be of value to the scientific community.

这项研究是在致力于钻探深层地热钻孔的欧洲 ORCHYD 项目期间进行的，在力学研究方面有许多潜在应用。它收集了斯堪的纳维亚（Kuru Grey 和 Red Bohus）和法国南部（Sidobre）三块露头花岗岩的地质描述。微观结构研究包括光学显微镜和 X 射线断层扫描。所选的三种花岗岩的晶粒大小涵盖了花岗岩的所有常见范围：细粒、中粒和粗粒。由于每种花岗岩的矿物相体积分数相似，因此对晶粒缺陷和晶粒边界进行了仔细研究，试图了解在实验室试样尺度下测量的三种花岗岩岩石样本的物理和机械性能。对岩石进行了 UCS、BTS 和三轴抗压强度测试，约束压力高达 225 兆帕或/和高应变速率高达 103/秒。重点介绍了影响力学行为的微观结构参数。试验结果表明，约束压力和应变速率对抗压强度的影响是不耦合的。然后，对这些影响进行了独立估算，并为超硬花岗岩系列提出了一个考虑到这两个变量的压缩断裂标准。该标准将每块岩石在 20 兆帕准静态约束应力下破坏时的偏差应力作为单一的参考强度测量值。然后将其与现有的准静态和动态数据集进行比较。关于这三种硬度极高的花岗岩（UCS ∼ 200 MPa）的完整数据集，以及用于破坏预测的综合方法，有可能为众多岩石工程项目提供信息，并对科学界具有重要价值。

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