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Research on the brittle characteristics of shale under long-term CO2-H2O-shale coupling effects 长期co2 - h2o -页岩耦合作用下页岩脆性特征研究

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-01 Epub Date: 2025-06-04 DOI: 10.1016/j.gete.2025.100696

Zhengjie Liu , Yongdong Jiang , Shizhe Song , Hongtao Zhang , Fuxin Guo

Hybrid fracturing focuses on optimizing the extraction of shale gas. In order to solve the issues of shale reservoir fracturing and CO₂ storage stability. Research was conducted to examine the mechanical properties of shale under long-term CO₂-H₂O-shale coupling effects. The results reveal that the SC-CO₂-H₂O-shale coupling effects increase shale porosity and pore size due to the dissolution of minerals. Concurrently, Shale cohesion and internal friction angle decrease. Following prolonged SC-CO₂-H₂O-shale coupling effects, there is a decline in shale strength and elastic modulus decline, alongside a decrease in axial strain (such as the growth of the compaction segment, but the shortening of the elastic and strain hardening segments). lateral strain increase, resulting in a higher Poisson's ratio. Additionally, the indices BI₁ rises by 47.44 %, whereas BI₂ drops by 66.85 %, improving the shale's drillability and cuttability. the indices BI₃, BI₄, BI₅, and BI₆ increase by 11.90 %, 45.10 %, 15.19 %, and 8.99 %, respectively, highlighting the shale's brittle characteristics. However, the indices BI₇, BI₈, and BI₉ decrease by 35.05 %, 38.20 %, and 46.67 %, indicating a reduction in the shale's fracturability. Confining pressure reduces lateral strain and increases axial strain, result in an increase in shale Poisson's ratio and strength. Following enhanced confining pressure, the indices BI₃ drops by 1.19–10.61 %, BI₄ decreases by 43.14–61.29 %, BI₅ falls by 1.27–14.29 %, and BI₆ declines by 1.12–8.42 %. Consequently, the failure characteristics transition from brittle to plastic. The SC-CO₂-H₂O-shale coupling effects facilitate the growth of fractures in unfractured areas. However, the elevated ground stress and reduced fracturability of the shale reservoirs restricts the growth of fractures in fractured zone, ensuring the stability of CO₂ storage.

混合压裂侧重于优化页岩气的开采。以解决页岩储层压裂及CO2储存稳定性问题。研究了长期co2 - h2o -页岩耦合作用下页岩的力学特性。结果表明，sc - co2 - h2o -页岩耦合作用增加了页岩孔隙度和孔隙尺寸。同时，页岩黏聚力和内摩擦角减小。随着sc - co2 - h2o -页岩耦合作用时间的延长，页岩强度和弹性模量下降，轴向应变减小（压实段增大，但弹性和应变硬化段缩短）。侧向应变增大，泊松比增大。BI1指数提高了47.44 %，BI2指数下降了66.85 %，提高了页岩的可钻性和可切削性。BI3、BI4、BI5、BI6指数分别上升11.90 %、45.10 %、15.19 %、8.99 %，表明页岩具有脆性特征。而BI7、BI8、BI9指数分别下降35.05 %、38.20 %、46.67 %，表明页岩可压性降低。围压降低了侧向应变，增大了轴向应变，导致页岩泊松比增大，强度增大。围压升高后，BI3指数下降1.19 ~ 10.61 %，BI4指数下降43.14 ~ 61.29 %，BI5指数下降1.27 ~ 14.29 %，BI6指数下降1.12 ~ 8.42 %。因此，破坏特征由脆性向塑性转变。sc - co2 - h2o -页岩耦合效应有利于裂缝发育。但由于地应力升高，页岩储层可压性降低，限制了裂缝区裂缝的发育，保证了CO2储层的稳定性。

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引用次数: 0

Centrifuge modelling of energy geostructures in soil: A review 土中能量土工结构的离心模拟研究进展

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-01 Epub Date: 2025-07-14 DOI: 10.1016/j.gete.2025.100719

Rui Zhao , Cong Shao , Jonathan Adam Knappett , Anthony Kwan Leung , Teng Liang , Liangtong Zhan , Yunmin Chen

Energy geostructures integrate heat exchange pipes of ground source heat pump systems within traditional underground structures, serving the dual purpose of extracting geothermal energy and supporting above-ground structures. The interaction between geothermal structures and soil involves heat transfer, pore pressure evolution and soil skeleton deformation, exhibiting a coupled thermo-hydro-mechanical response. Although detailed numerical and analytical models have been developed to analyze the thermo-hydro-mechanical behaviour of energy geostructures in soil, significant challenges remain in validating this coupled response. Centrifuge modelling provides prototype confining stresses in reduced-scale models, providing an alternative to field measurements with more controllable conditions and at lower cost. This paper reviews the current state of the art of centrifuge modelling of energy geostructure–soil interaction, with a particular focus on (i) scaling laws; (ii) evaluations of existing heating and cooling systems; (iii) soil modelling, including material selection and model preparation; and (iv) scale modelling of energy geostructural elements. Each section emphasizes the challenges of centrifuge modelling and presents identified solutions to these challenges. Finally, the prospect for future studies is discussed, highlighting the potential to enhance understanding of the underlying mechanisms controlling thermo-hydro-mechanical behaviour of geothermal structures in soil.

能源土工构筑物将地源热泵系统的换热管道集成在传统地下构筑物内，起到提取地热能和支撑地上构筑物的双重作用。地热构造与土壤的相互作用涉及传热、孔隙压力演化和土壤骨架变形，表现出热-水-力耦合响应。尽管已经开发了详细的数值和分析模型来分析土壤中能量土工结构的热-水-力学行为，但在验证这种耦合响应方面仍然存在重大挑战。离心机建模提供了缩小比例模型的原型围应力，为现场测量提供了更可控条件和更低成本的替代方案。本文回顾了能量土工结构-土壤相互作用的离心模型的现状，特别关注(i)标度定律；（ii）评估现有的加热及冷却系统；（iii）土壤建模，包括材料选择和模型准备；（四）能量土工结构单元的尺度建模。每个部分都强调了离心机建模的挑战，并提出了应对这些挑战的确定解决方案。最后，讨论了未来研究的前景，强调了加强对控制土壤地热结构热-水-力学行为的潜在机制的理解的潜力。

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引用次数: 0

Experimental and numerical analysis of hydraulic fracture propagation in naturally fractured granite cores 天然裂缝花岗岩岩心水力裂缝扩展的实验与数值分析

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-01 Epub Date: 2025-06-06 DOI: 10.1016/j.gete.2025.100695

Jia He , Li Zhuang , Muzi Li , Zhou Zhou

Understanding hydraulic fracture (HF) propagation in naturally fractured granite reservoir is of great importance for deep geothermal energy exploitation. We first conducted laboratory hydraulic fracturing tests on granite outcrops containing natural fractures (NF) and observed deflection of HF toward the NF in a parallel-approach case, and arrested HF in a perpendicular-approach case. Then, a two-dimensional discrete element model is employed to analyze coupled hydro-mechanical processes in the experiments. Our modeling results reveal that, for a parallel-approach case, HF tends to deflect toward the NF when the normal distance between the HF propagation path and NF is less than 5 mm (equivalent to borehole diameter). HF crossing at perpendicular-approach case was found to occur only when two conditions are met: (i) the maximum principal stress at the intersection exceeds the tensile strength of rock, and (ii) no shear failure occurs in NF. Finally, we examined the combined effects of approach angle, NF friction coefficient, and differential principal stress under a constant minimum principal stress (σ_h) of 10 MPa. HF crossing occurred only when the differential principal stress (σ_H - σ_h) ≥ 3 MPa, and was further promoted by larger approach angles (e.g., θ > 50°) and higher NF friction coefficients (e.g., μ > 0.4).

了解天然裂缝型花岗岩储层水力裂缝的扩展规律对深部地热能开发具有重要意义。我们首先对含有天然裂缝（NF）的花岗岩露头进行了实验室水力压裂试验，观察了在平行接近的情况下HF向NF的偏转，在垂直接近的情况下HF被阻止。然后，采用二维离散元模型对实验中的水-力耦合过程进行分析。模拟结果表明，在平行接近的情况下，当HF传播路径与NF之间的法向距离小于5 mm（相当于钻孔直径）时，HF倾向于向NF偏转。在垂直接近的情况下，只有满足两个条件才会发生HF交叉：(1)相交处的最大主应力超过岩石的抗拉强度；(2)NF不发生剪切破坏。最后，在最小主应力（σh）为10 MPa的恒定条件下，考察了进近角、NF摩擦系数和差主应力的综合效应。只有当主应力差(σH - σH)≥ 3 MPa时才会发生HF交叉，较大的进近角(如θ >；50°)和更高的NF摩擦系数(例如μ >；0.4)。

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引用次数: 0

Thermal influence zone of energy tunnels in sandy soils under the hydrostatic condition 静水条件下砂土能量隧道热影响区

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-01 Epub Date: 2025-07-13 DOI: 10.1016/j.gete.2025.100716

Alaaeldin Magdy , Alice Di Donna , Hussein Mroueh

Energy geostructures are more and more considered as a possible solution to cover heating and cooling needs. They function according to the principle of shallow geothermal energy, exchanging heat with the ground. This results in a zone underground where the temperature of the ground is affected by the presence of the geothermal system, which is called thermal influence zone. As the number of energy geostructures increases, determining their thermal influence zone becomes crucial, especially in environments where adjacent energy geostructures or other geothermal systems coexist. Indeed, avoid or minimize the overlap between the thermal influence zones of different geothermal installations is important to ensure their efficiency. This study investigates the effects of groundwater level, thermal operation period, and ground permeability, in both heating and cooling modes, on the thermal influence zone generated around an energy tunnel. The results indicate that the thermal induced change in groundwater density and viscosity due to geothermal operations generates groundwater circular flows. These flows play a major role in shaping the thermal influence zone. In the heating mode (winter), when the groundwater is within the vicinity of the tunnel, i.e., above, at or just below the tunnel, the thermal influence zone takes an oval shape elongated below the tunnel invert. In the cooling mode (summer), the thermal influence zone does not follow a specific shape, and it is remarkably changed by the groundwater level. For instance, when the groundwater level is shallow, the thermal influence zone extends significantly upward, potentially overlapping with the surface layer affected by atmospheric air temperature. However, when the groundwater level at the tunnel centreline, the thermal influence zone takes a horizontal oval shape, which might interfere with adjacent similar installations. The expansion of the thermal influence zone is highly dependent on the operation duration. In winter, the downward elongation after 6 months operation reaches around 1.5 times that after 3 months.

能源土工结构越来越被认为是满足供暖和制冷需求的可能解决方案。它们根据浅层地热能原理工作，与地面交换热量。这就产生了地下的一个区域，在这个区域里，地面的温度受到地热系统的影响，这个区域被称为热影响区。随着能源土工结构数量的增加，确定其热影响区变得至关重要，特别是在邻近能源土工结构或其他地热系统共存的环境中。事实上，避免或尽量减少不同地热装置的热影响区之间的重叠对于确保其效率非常重要。研究了地下水位、热力运行周期和地下渗透率对能量隧道周边热影响区的影响。结果表明，地热开采引起的地下水密度和粘度的热致变化产生了地下水循环流动。这些气流在形成热影响区方面起主要作用。在采暖模式下（冬季），当地下水处于隧道附近，即隧道上方、下方或下方时，热影响区在隧道仰拱下方呈椭圆形拉长。在降温模式下（夏季），热影响区不遵循特定的形状，受地下水位的影响变化显著。例如，当地下水位较浅时，热影响区明显向上延伸，可能与受大气温度影响的表层重叠。然而，当地下水位在隧道中心线时，热影响区呈水平椭圆形，可能会干扰邻近的类似设施。热影响区的扩展高度依赖于运行时间。冬季手术6个月后的下伸率达到3个月后的1.5倍左右。

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引用次数: 0

Energy evolution and distribution patterns of sandstone and its microscopic mechanism under multistage cyclic loading 多级循环加载下砂岩能量演化分布规律及微观机制

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-01 Epub Date: 2025-06-01 DOI: 10.1016/j.gete.2025.100694

Hongying Tan , Hejuan Liu , Chunhe Yang , Haijun Mao , Yujia Song , Debin Xia , Shengnan Ban , Weimin Wang

Sandstone, as a fundamental engineering material in depleted oil and gas reservoir gas storage systems, is susceptible to damage and failure under periodic stress disturbances. In this study, multi-level multi-cyclic loading tests were carried out on sandstone samples over the confining pressures range of 5–40 MPa, accompanied by real-time acoustic emission (AE) monitoring and periodic nuclear magnetic resonance (NMR) measurements. This study investigats the effects of confining pressure, stress level, and the number of cycles on energy evolution and energy distribution in rock, revealing the micromechanisms of energy evolution during cyclic loading. The results indicate that during the first cyclic loading, the input energy is primarily converted into dissipated energy through the compression of small pores and some medium pores. In subsequent loading cycles, the input energy is primarily converted into dissipated energy through the initiation and propagation of internal microcracks. Under high confining pressure, the rock transitions from brittle to ductile behavior, enabling it to withstand greater deformation. Additionally, at high confining pressure, rocks accumulate more strain energy, while energy dissipation is higher compared to lower confining pressures. Throughout the cyclic loading, dissipated energy consistently accounts for less than 30 % of the total input energy across all stress levels. The linear energy storage coefficient remains independence from stress level and cycle number, but exhibits an inverse relationship with confining pressure. There is an obvious linear relationship between rock dissipation energy and AE energy. Higher AE energy indicate that the rock dissipates more strain energy.

砂岩作为衰竭油气藏储气系统的基础工程材料，在周期性应力扰动下易发生破坏。在5 ~ 40 MPa围压范围内，对砂岩试样进行了多级多循环加载试验，并进行了实时声发射（AE）监测和周期性核磁共振（NMR）测量。研究了围压、应力水平和循环次数对岩石能量演化和能量分布的影响，揭示了循环加载过程中能量演化的微观机制。结果表明：在第一次循环加载过程中，输入能量主要通过压缩小孔隙和部分中等孔隙转化为耗散能量；在随后的加载循环中，输入能量主要通过内部微裂纹的萌生和扩展转化为耗散能量。在高围压下，岩石从脆性转变为延性，使其能够承受更大的变形。高围压条件下，岩石积累的应变能更多，能量耗散也比低围压条件下大。在整个循环加载过程中，耗散能量始终占所有应力水平下总输入能量的30% %以下。线性蓄能系数与应力水平和循环次数无关，与围压呈反比关系。岩石耗散能与声发射能之间存在明显的线性关系。声发射能越高，说明岩石耗散的应变能越大。

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引用次数: 0

Hydromechanical simulation of argillaceous rocks: From laboratory tests to drift excavation 泥质岩石的流体力学模拟：从实验室试验到进路开挖

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-01 Epub Date: 2025-07-09 DOI: 10.1016/j.gete.2025.100714

Davood Yazdani Cherati , Jean Vaunat , Antonio Gens Solé , Carlos Plua , Minh Ngoc Vu , Gilles Armand

This study aims to evaluate the role of the pre-peak hardening regime in an elasto- viscoplastic model for argillaceous rocks, called the argillite model, use the model to replicate the hydromechanical response of argillaceous rocks observed in both laboratory and field tests, and investigate the interactions between excavation supports and these geomaterials. Initially, the impacts of the pre-peak strain hardening regime on behavior of argillaceous rocks are investigated through modeling a series of theoretical biaxial tests. Afterward, the model is validated by simulating biaxial and triaxial tests conducted on Beaucaire marl and Callovo-Oxfordian (COx) clay samples, respectively. Additionally, the role of the hardening regime in capturing the dependence of strain at peak strength on confining pressure is demonstrated using the triaxial models. Next, the effects of the hardening regime on the hydromechanical response of argillaceous rocks to drift excavations are demonstrated by modeling GCS drift, excavated within the Meuse/Haute-Marne Underground Research Laboratory (MHM URL). Subsequently, the argillite model is employed to simulate three other supported and unsupported drifts, excavated within the MHM URL. Finally, the long-term failure pattern of the concrete lining is predicted. Results indicate that incorporating the hardening regime and support effects can significantly enhance the accuracy of the model predictions.

本研究旨在评估峰值前硬化机制在泥岩弹粘塑性模型（即泥岩模型）中的作用，利用该模型复制实验室和现场试验中观察到的泥岩流体力学响应，并研究开挖支架与这些岩土材料之间的相互作用。首先，通过模拟一系列理论双轴试验，研究了峰前应变硬化对泥质岩石行为的影响。随后，分别在Beaucaire泥灰岩和Callovo-Oxfordian （COx）粘土样品上进行了双轴和三轴模拟试验，对模型进行了验证。此外，使用三轴模型证明了硬化机制在捕获峰值强度下应变对围压的依赖中的作用。接下来，通过模拟在默兹/上马恩地下研究实验室（MHM URL）挖掘的GCS漂移，验证了硬化机制对泥质岩石对漂移开挖的水力学响应的影响。随后，利用泥质岩模型模拟了在MHM URL内开挖的另外三个有支撑和无支撑的巷道。最后，对混凝土衬砌的长期破坏模式进行了预测。结果表明，考虑硬化机制和支撑效应可以显著提高模型预测的准确性。

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引用次数: 0

Evaluation of acid fracturing in carbonatite geothermal reservoirs based on a coupled thermo-hydro-mechanical-chemical model considering discrete fracture networks 考虑离散裂缝网络的热-水-力-化学耦合模型碳酸盐岩地热储层酸压评价

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-01 Epub Date: 2025-06-18 DOI: 10.1016/j.gete.2025.100704

Jia Liu , Wenqi Zhang , Yi Xue , Huimin Wang , Shi-Tong Li , Yun Zhang , Weihua Li

In the development of carbonate geothermal reservoirs, the implementation of acid fracturing technology is common and essential, effectively enhancing reservoir permeability. It encompasses a sequence of intricate phenomena including solute migration, acid-rock reaction, heat transfer, and deformation. Herein, a comprehensive thermo-hydro-mechanical-chemical (THMC) coupling model considering field-scale discrete fracture networks (DFNs) is established for the process. With the thin elastic layer and fracture element assumptions, the corrosion and deformation of fractures are considered simultaneously. Additionally, the model accounts for the corrosion effects of both bedrock and fracture surfaces, and tracks the evolution of fracture aperture and matrix porosity. Using the proposed model, this study investigates acid fracturing in varying reservoir and operational conditions. It is found that the connectivity of DFN can influence the seepage path of acid fluid, therefore affecting acid concentration transport, which has a significant impact on the reconstruction of reservoir acidification. The acidification effectiveness nonlinearly positively correlates to the rate and concentration of acid injection, while the change of chemical aperture is negatively correlated to the initial fracture aperture. Reservoir temperature has a limited influence on acidification outcomes. The scientific insights provided here are valuable in steering the optimization of acid fracturing in carbonatite reservoirs.

在碳酸盐岩地热储层开发中，实施酸压技术是普遍和必不可少的，能有效提高储层渗透率。它包含了一系列复杂的现象，包括溶质迁移、酸岩反应、传热和变形。在此基础上，建立了考虑现场尺度离散裂缝网络（DFNs）的热-水-机械-化学（THMC）综合耦合模型。采用薄弹性层和断裂单元假设，同时考虑了断裂的腐蚀和变形。此外，该模型考虑了基岩和裂缝表面的腐蚀效应，并跟踪裂缝孔径和基质孔隙度的演变。利用所提出的模型，研究了不同储层和作业条件下的酸压裂。研究发现，DFN的连通性会影响酸性流体的渗流路径，从而影响酸浓度的输运，对储层酸化改造有重要影响。酸化效果与注酸速率和注酸浓度呈非线性正相关，而化学孔径的变化与初始裂缝孔径呈负相关。储层温度对酸化效果的影响有限。本文提供的科学见解对于指导碳酸盐岩储层酸压裂的优化具有重要价值。

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引用次数: 0

Thermo-mechanical coupling damage constitutive relation of thermally treated rocks: Statistical modeling and verification 热处理岩石热-机耦合损伤本构关系：统计建模与验证

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-01 Epub Date: 2025-06-23 DOI: 10.1016/j.gete.2025.100708

Peilei Zhang, Linqi Huang, Xibing Li

Under the inherent high temperature conditions, the rock will obviously be damaged and deteriorated. Developing an objective and rational thermo-mechanical coupling constitutive model is the key to directly assess the rock strength and deformation behavior within a thermodynamic framework. The classical damage model, relying on the strain equivalent hypothesis, struggles to accurately describe the real nonlinear behavior at the compaction stage. For thermally treated rocks, this significantly leads to a larger evolution error. This paper introduces a strain correction method for obtaining effective strain by separating the compaction strain. On this basis, a novel thermo-mechanical coupling statistical constitutive model is developed. Compared to the classical and existing models, the proposed coupling constitutive model demonstrates superior capabilities in describing the uniaxial strength and deformation characteristics under constant heating and heating cycles, especially for the compaction and post-peak strain softening states. Furthermore, the thermo-mechanical coupling damage evolution is analyzed. As temperature increases, the initial damage increases, the experienced deformation also increases, and the overall damage development trends to be flat. In contrast, the influence of heating cycles on rock damage is more significant than that of direct heating. The integration of macroscopic thermodynamic degradation and statistical characterization in constitutive modeling is a reasonable analytical approach, with the parameters have clearly physical meaning. These results can serve as a reference for the thermodynamic constitutive theory in relation to deep rock engineering.

在固有的高温条件下，岩石会发生明显的破坏变质。建立客观合理的热-力耦合本构模型是在热力学框架下直接评价岩石强度和变形行为的关键。经典损伤模型依赖于应变等效假设，难以准确描述压实阶段的实际非线性行为。对于经过热处理的岩石，这明显导致较大的演化误差。本文介绍了一种通过分离压实应变获得有效应变的应变校正方法。在此基础上，建立了一种新的热力耦合统计本构模型。与经典模型和现有模型相比，本文提出的耦合本构模型能够更好地描述恒定加热和加热循环下的单轴强度和变形特性，特别是对压实和峰后应变软化状态。进一步分析了热-机耦合损伤演化过程。随着温度的升高，初始损伤增加，经历的变形也增加，整体损伤发展趋势趋于平缓。相比之下，加热循环对岩石损伤的影响比直接加热更显著。将宏观热力学退化与统计表征相结合的本构建模是一种合理的分析方法，参数具有明确的物理意义。研究结果可为深部岩体工程的热力学本构理论提供参考。

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引用次数: 0

Thermally induced tensile hoop stresses in energy piles: Implications for design and operation 能源桩的热致拉箍应力：对设计和操作的影响

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-01 Epub Date: 2025-06-17 DOI: 10.1016/j.gete.2025.100702

Ugur Can Erginag , Mert Guner , Semra Polat , Melis Sutman , Ozer Cinicioglu

Energy piles, also known as thermoactive piles, serve a dual purpose: providing structural stability and harvesting shallow geothermal energy. As such, their design must account for both structural and thermal loads. However, current practice typically considers only the axial components of thermal loads. This study aims to investigate thermal loads in three dimensions, with a particular focus on tensile hoop stresses in the clear concrete cover. Through numerical modelling, this study examines the positional and temporal variations of hoop stresses and elucidates the underlying mechanisms. The findings demonstrate that significant tensile hoop stresses can develop within the clear concrete cover during the operation of energy piles, and that these stresses shift positions with seasonal operational changes. Therefore, it is crucial to consider hoop stresses in the design of energy piles to prevent the exceedance of concrete’s structural tensile capacity, a major design concern. A sensitivity analysis was conducted, varying material properties, geometric aspects and operational preferences to identify the relationships between influential parameters and hoop stresses. The study concludes with design and operational recommendations based on these findings.

能源桩，也被称为热活性桩，有双重目的：提供结构稳定性和收集浅层地热能。因此，它们的设计必须同时考虑结构和热负荷。然而，目前的做法通常只考虑热负荷的轴向分量。本研究旨在研究三维热载荷，特别关注透明混凝土覆盖层中的拉箍应力。通过数值模拟，本研究考察了环向应力的位置和时间变化，并阐明了潜在的机制。研究结果表明，能源桩运行过程中，透明混凝土覆盖层内会产生显著的拉箍应力，且这些应力随运行季节的变化而发生位移。因此，在能源桩设计中考虑环向应力是防止混凝土结构抗拉能力超出的重要设计问题。对不同的材料特性、几何方面和操作偏好进行了敏感性分析，以确定影响参数与环向应力之间的关系。该研究总结了基于这些发现的设计和操作建议。

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引用次数: 0

Study on the fracture propagation rule of simultaneous fracturing under cyclic injection 循环注入条件下同时压裂裂缝扩展规律研究

IF 3.3 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-01 Epub Date: 2025-07-03 DOI: 10.1016/j.gete.2025.100711

Ge Zhu , Chuanli Wei , Jingna Liu

Simultaneous fracturing has emerged as a pivotal technology in unconventional oil and gas development, offering significant advantages in enhancing operational efficiency and reducing costs. However, plagued by stress shadow, non-uniform propagation of multiple fractures may occur during the operation, resulting in the stimulated reservoir volume (SRV) failing to meet the requirements. This study proposes an innovative scheme of utilizing cyclic injection to alleviate stress shadow. The dynamic stress generated by cyclic injection can complicate the interaction of multiple fractures during propagation, increasing the complexity of the fracture network. Furthermore, a numerical simulation model of multi-fracture propagation during simultaneous fracturing under cyclic injection was established using the extended finite element method (XFEM). The impact of the temporal modulation parameters governing cyclic injection scheme, including period, amplitude and phase, on the fracture propagation was discussed. Finally, an operational scheme was proposed in which different operating wells use distinct cyclic injection rates during simultaneous fracturing. The results reveal that cyclic injection scheme can significantly alleviate the fracture propagation disparities caused by stress shadow compared to conventional constant injection mode. The period, amplitude, and phase of cyclic injection rate exert critical control over fracture propagation morphology during simultaneous fracturing operations. Notably, the implementation of different cyclic injection schemes for various operating wells represents a deliberate attempt to alleviate stress shadow and improve fracture complexity. The research results can provide guidance for the field application of simultaneous fracturing and significantly contribute to improving the SRV.

同时压裂已成为非常规油气开发的关键技术，在提高作业效率和降低成本方面具有显著优势。然而，由于受应力阴影的影响，在作业过程中可能出现多条裂缝的不均匀扩展，导致增产储层体积（SRV）达不到要求。本研究提出了一种利用循环注射来缓解应力阴影的创新方案。循环注入产生的动应力会使多条裂缝在扩展过程中的相互作用复杂化，增加裂缝网络的复杂性。在此基础上，采用扩展有限元法（XFEM）建立了循环注入条件下同时压裂过程中多裂缝扩展的数值模拟模型。讨论了周期、振幅和相位等控制循环注入方案的时间调制参数对裂缝扩展的影响。最后，提出了不同作业井在同时压裂过程中使用不同循环注入速率的作业方案。结果表明，与常规恒注入相比，循环注入方案能显著缓解应力阴影引起的裂缝扩展差异。在同步压裂作业中，循环注入速率的周期、幅度和相位对裂缝扩展形态起着至关重要的控制作用。值得注意的是，针对不同的作业井实施不同的循环注入方案，表明了有意缓解应力阴影和提高裂缝复杂性的尝试。研究成果可为同时压裂的现场应用提供指导，对提高SRV具有重要意义。

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