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A machine learning-based thermal-mechanical parameter inversion of energy pile considering thermo-mechanical behaviors 考虑热力学行为的基于机器学习的能量桩热力学参数反演

IF 3.7 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-28 DOI: 10.1016/j.gete.2025.100752

Chaoran Wang, Jiaxin Liu, Gia Trung Luu, Chanjuan Han

The thermal-mechanical properties of rock-soil are indispensable for the geotechnical investigation of energy piles according to design codes. The thermal parameters of the stratum and pile are commonly determined through thermal response tests (TRT), and the mechanical parameters are obtained via sampling or in-situ testing, with some parameters also assigned based on engineering experience. However, on the one hand, TRT and in-situ testing are costly and labor-intensive processes that last nearly one week. On the other hand, the accuracy of personal experience on parameter determination is not guaranteed. Parameter inversion adjusts numerically modelled values (originally from tests/experience) to compensate for sampling effects, stratigraphic variations, and human biases that create simulation errors. The machine learning-based surrogate model, experiencing a surge in popularity in recent years, is a promising solution for inversion acceleration. By training on precomputed numerical simulation results, the surrogate model emulates the system’s behavior at significantly faster speeds, simultaneously reducing computational time and financial costs compared to traditional numerical modelling. This study proposes a novel method for parameter inversion with machine-learning-based surrogate models. A numerical model is first established by replicating a reduced-scale physical test capturing the thermal-mechanical behaviors of the energy pile. The Latin hypercube sampling is subsequently utilized to generate sufficient data for XGBoost model development, where the sensitivity analysis is subsequently carried out for parameter screening. The parameter inversion is then implemented with non-dominated sorting genetic algorithms. The effectiveness of the method is validated using 4 real-case test conditions. The results demonstrate that the surrogate model attains high accuracy with an R² of temperature and axial forces above 0.97 and 0.9, respectively. Lastly, the results of parameter inversion indicate a promising and optimistic prospect for the proposed inversion method, which can reveal the comprehensive parameters of the material to a certain extent. This study presents an efficient method for parameter inversion of energy piles while providing a perspective of fast determination of rock-soil thermal properties.

根据设计规范进行能源桩岩土工程勘察时，岩土热力学特性是必不可少的。地层和桩的热参数一般通过热响应试验（TRT）确定，力学参数一般通过抽样或现场测试获得，部分参数也根据工程经验确定。然而，一方面，TRT和原位测试是一个耗时近一周的昂贵和劳动密集型过程。另一方面，不能保证个人经验对参数确定的准确性。参数反演调整数值模拟值（最初来自测试/经验），以补偿采样效应、地层变化和造成模拟误差的人为偏差。基于机器学习的代理模型近年来越来越受欢迎，是一种很有前途的反演加速解决方案。通过对预先计算的数值模拟结果进行训练，代理模型可以以更快的速度模拟系统的行为，同时与传统的数值模拟相比，减少了计算时间和财务成本。本研究提出了一种基于机器学习的代理模型参数反演的新方法。首先通过模拟能量桩的小尺度物理试验，建立了能量桩的数值模型。随后利用拉丁超立方体采样为XGBoost模型开发生成足够的数据，随后进行敏感性分析以进行参数筛选。然后用非支配排序遗传算法实现参数反演。通过4个实际测试条件验证了该方法的有效性。结果表明，该模型具有较高的拟合精度，温度和轴向力的R2分别在0.97和0.9以上。最后，参数反演结果表明，所提出的反演方法具有良好的应用前景，能在一定程度上揭示材料的综合参数。该研究为能量桩参数反演提供了一种有效的方法，同时为快速确定岩土热特性提供了前景。

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引用次数: 0

Shape effect of shear box in large-scale direct shear test for soil-rock mixture 土石混合体大尺度直剪试验中剪切箱形状效应研究

IF 3.7 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-25 DOI: 10.1016/j.gete.2025.100750

Yiliang Tu , Quanlin Huang , Qianglong Yao , Zhong Fang , Xinrong Liu , Hejun Chai

The large-scale direct shear test is one of the simplest and most efficient methods for testing the shear strength parameters of soil-rock mixtures (S-RM), with shear boxes available in various shapes such as circular and rectangular. However, it remains unclear whether the shear box shape affects the accuracy of the results from large-scale direct shear tests. Therefore, this study uses a three-dimensional (3D) discrete element method to construct a numerical model for large-scale direct shear tests on S-RM, accounting for realistic rock block shapes. Subsequently, the reliability of this numerical model was validated by comparing it with results from large-scale direct shear tests laboratory. Next, the direct shear test results of the same S-RM were compared between circular and square shear boxes. The results indicate that the test results in the square shear box are more accurate. In the circular shear box, the test results approximate those in the square shear box, but their deformation is not a strict plane strain. Finally, the influence of the length-width ratio (L/W) of the shear box on results of large-scale direct shear tests on S-RM is discussed. Results show that as the L/W decreases, the interlocking effect between rock blocks strengthens, the number of force chains increases, and the shear band thickness decreases; the stress-strain curve transitions from strain-softening to strain-hardening; both cohesion and internal friction angle exhibit two distinct trends within the range before and after the L/W reaches 1:1. Thus, in large-scale direct shear tests of S-RM, square shear boxes with a L/W of 1:1 are preferred, followed by rectangular shear boxes with a L/W greater than 1:1, while shear boxes with a L/W less than 1:1 should be avoided.

大型直剪试验是测试土石混合体抗剪强度参数最简单、最有效的方法之一，剪切箱有圆形和矩形等多种形状。然而，剪切箱的形状是否会影响大型直剪试验结果的准确性尚不清楚。因此，本研究采用三维（3D）离散元方法，在考虑真实岩块形状的情况下，构建S-RM大尺度直剪试验数值模型。通过与室内大型直剪试验结果的对比，验证了该数值模型的可靠性。接下来，比较了圆形和方形剪切箱对同一S-RM的直剪试验结果。结果表明，方形剪切箱的试验结果更为准确。在圆形剪切箱中，试验结果与方形剪切箱中的试验结果接近，但它们的变形不是严格的平面应变。最后，讨论了剪切箱长宽比（L/W）对S-RM大型直剪试验结果的影响。结果表明：随着L/W的减小，岩块间的联锁效应增强，力链数增加，剪切带厚度减小；应力-应变曲线由应变软化过渡到应变硬化；黏聚力和内摩擦角在L/W达到1:1前后表现出明显的变化趋势。因此，在S-RM大型直剪试验中，首选L/W为1:1的方形剪切箱，其次是L/W大于1:1的矩形剪切箱，而L/W小于1:1的剪切箱应避免使用。

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引用次数: 0

Load transfer analysis of driven energy pile under combined thermal and mechanical loading 热-力复合荷载作用下动力桩的荷载传递分析

IF 3.7 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-25 DOI: 10.1016/j.gete.2025.100751

Changyi Yang , Jingpei Li , Guiwei Tian , Chang Liu , Ning Lai

This study presents a semi-analytical analysis on load transfer mechanisms of driven energy piles in clay, with a comprehensive consideration of installation effects, reconsolidation of surrounding soils and combined thermal and mechanical loading. The installation effects of driven energy piles are modelled based on the cavity expansion theory. Analytical expressions for thermally induced displacements, including axial and radial expansion of pile, are derived. A hysteresis hyperbolic load transfer function is proposed according to the Masing’s criterion to incorporate the loading and unloading induced by temperature changes. Through numerical simulations and experimental validations, the axial strain and stress distribution within the pile under varying conditions is explored, where good agreements between the proposed theoretical method, numerical results and field tests are observed. A thorough comparison is conducted between driven energy piles and bored energy piles to assess the impact of installation effects on pile-soil relative displacement, shaft friction, and the ultimate bearing capacity. It is found that although the bearing capacity of driven energy piles is greater than that of bored energy piles, the axial stress within driven energy piles is also higher under thermal load. The findings shed light on the design and optimization of PHC energy piles in geothermal systems.

综合考虑安装效应、周围土体的再固结和热力复合荷载，对粘土中动力桩的荷载传递机理进行了半解析分析。基于空腔膨胀理论，对动力桩的安装效果进行了模拟。导出了热致位移的解析表达式，包括桩的轴向和径向扩展。根据Masing准则，提出了一个包含温度变化引起的加载和卸载的滞后双曲荷载传递函数。通过数值模拟和试验验证，探讨了不同工况下桩内的轴向应变和应力分布，理论方法、数值结果和现场试验结果吻合较好。对动力桩和钻孔动力桩进行了全面对比，评估了安装效应对桩土相对位移、桩身摩擦和极限承载力的影响。研究发现，虽然打入能源桩的承载力大于钻孔能源桩，但在热荷载作用下，打入能源桩内部的轴向应力也更高。研究结果为地热系统中PHC能源桩的设计与优化提供了参考。

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引用次数: 0

Quantitative prediction of tertiary formation fractures and its application in lost circulation prediction in the Bozhong Depression 渤中坳陷第三系裂缝定量预测及其在漏失预测中的应用

IF 3.7 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-24 DOI: 10.1016/j.gete.2025.100749

He Du , Jianwei Feng , Shouyu Xu , Junxiao Qu , Chen Li , Xiang Gao , Huilin Xing

In recent years, the exploration and development of oil and gas reservoirs in the Bohai Sea have gained significant attention. However, the high cost of offshore drilling and the occurrence of frequent lost circulation accidents have resulted in substantial economic losses. Therefore, it is crucial to effectively predict and assess the risk of lost circulation in the Bozhong Depression. This study focuses on the analysis of lost circulation characteristics, identifying fracture characteristics as the most influential factors. Geomechanical methods were employed to characterize fracture parameters in the study area, enabling the prediction of lost circulation. A three-dimensional heterogeneous rock mechanical parameter model, incorporating lithology and faults, was constructed based on rock mechanics experiments, logging, and seismic data. Structural evolution analysis and acoustic emission experiments were conducted to determine the main period of fracture development. The Ansys software's finite element simulation platform facilitated the simulation of the paleo-stress field in the study area. By applying the principles of geomechanics, a calculation formula for fracture parameters was derived, and the spatial distribution of fracture parameters in the study area was quantitatively characterized using the results of the paleo-stress field simulation. Taking into account the lost circulation points of drilled wells, fracture parameters, current stress field, lithology, and other factors contributing to lost circulation, a leakage risk threshold area for fracture parameters was proposed. The predictions of lost circulation were validated using verification wells, demonstrating good agreement with actual drilling conditions. This approach provides valuable insights for mitigating lost circulation during drilling, reducing drilling cycles, and minimizing economic losses.

近年来，渤海地区的油气勘探与开发备受关注。然而，海上钻井成本高，漏失事故频发，造成了巨大的经济损失。因此，有效地预测和评估渤中坳陷的漏失风险至关重要。本研究重点分析了漏失特征，认为裂缝特征是影响漏失最主要的因素。利用地质力学方法对研究区域的裂缝参数进行表征，从而预测井漏情况。基于岩石力学实验、测井和地震资料，建立了考虑岩性和断层的三维非均质岩石力学参数模型。通过构造演化分析和声发射实验确定了裂缝发育的主要时期。利用Ansys软件的有限元仿真平台，实现了研究区古应力场的模拟。应用地质力学原理，推导了裂缝参数计算公式，并利用古应力场模拟结果定量表征了研究区裂缝参数的空间分布。综合考虑井漏点、裂缝参数、当前应力场、岩性等导致漏失的因素，提出了裂缝参数的泄漏风险阈值区域。利用验证井对漏失预测进行了验证，与实际钻井条件吻合良好。该方法为减少钻井过程中的漏失、缩短钻井周期、最大限度地减少经济损失提供了宝贵的见解。

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引用次数: 0

Discrimination of critically stressed faults and safety-optimized hydraulic fracturing design: Insights from meter-scale physical modeling 临界应力断层的识别和安全优化水力压裂设计：来自米尺度物理建模的见解

IF 3.7 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-23 DOI: 10.1016/j.gete.2025.100748

Xiaodong Wang , Qianting Hu , Baocai Wang , Chunhui Cheng , Yongjiang Luo

This study presents an integrated approach combining metre-scale physical experiments, numerical simulations and theoretical modelling to systematically investigate the mechanisms and controlling factors of fault slip induced by hydraulic fracturing, with the ultimate goal of establishing fundamental design principles for fault slip mitigation. First, we quantify the influence of fault geometry and mechanical properties on stress concentration by deriving a quantitative stress concentration equation through multivariate regression analysis. Second, a novel three-dimensional (3D) Coulomb failure stress (CFS) expression incorporating stress concentration coefficients is proposed to overcome the limitations of conventional regional stress analysis. Third, the theoretical stress transfer model is validated against experimental data, showing strong agreement between predicted and measured CFS changes, with a relative error of less than 10 %. Our results demonstrate that hydraulically isolated faults are primarily controlled by regional stress states during slip initiation. Critically stressed faults exhibit significant slip near injection points, while non-critical faults remain stable. The proposed 3D CFS expression successfully discriminates between stress-transfer induced PNR-1z and pore-pressure driven PNR-2 seismic events. Finally, faults are classified into four distinct types, each associated with tailored hydraulic fracturing design protocols: type I faults require mandatory avoidance; type II-III faults require controlled injection parameters; and type IV faults permit cost-optimised operations. These findings provide theoretical advances and practical guidelines for mitigating induced seismicity in hydraulic fracturing.

本研究采用米尺度物理实验、数值模拟和理论建模相结合的综合方法，系统研究水力压裂诱发断层滑动的机理和控制因素，最终建立断层滑动缓解的基本设计原则。首先，通过多元回归分析，推导出定量应力集中方程，量化断层几何形状和力学性质对应力集中的影响。其次，针对传统区域应力分析的局限性，提出了一种包含应力集中系数的三维库仑破坏应力（CFS）表达式。第三，将理论应力传递模型与实验数据进行对比验证，结果表明，CFS变化预测值与实测值吻合较好，相对误差小于10 %。研究结果表明，水力隔离断层主要受起滑过程中区域应力状态的控制。临界应力断层在注入点附近表现出明显的滑移，而非临界断层则保持稳定。提出的三维CFS表达式成功区分了应力传递诱发的PNR-1z和孔隙压力驱动的PNR-2地震事件。最后，将断层分为四种不同的类型，每种类型都与定制的水力压裂设计方案相关：I型断层需要强制规避；II-III型故障需要控制注入参数；IV型故障可以实现成本优化操作。这些发现为减轻水力压裂诱发地震活动提供了理论进展和实践指导。

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引用次数: 0

Damage simulation of casing-cement interface of wellbore structure under non-uniform formation stress 非均匀地层应力下井筒结构套管-水泥界面损伤模拟

IF 3.7 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-18 DOI: 10.1016/j.gete.2025.100747

Fei Li , Yongsheng Liu , Haoran Xu , Feng Tang , Lihong Han , Shangyu Yang

In ultra-deep drilling operations, formations such as creeping mudstone and high-pressure salt layers are frequently encountered, generating non-uniform loads that pose severe challenges to casing design and wellbore integrity. The interfacial bonding behavior between the cement sheath and casing is a critical factor governing the long-term integrity of the wellbore. This paper develops a damage model for the double-layer casing-cement sheath interface under non-uniform loading based on peridynamic theory. The model numerically characterizes the evolution mechanism of interface damage under non-uniform stress. Laboratory tests were conducted using a Digital Image Correlation (DIC) system to capture the strain evolution on the casing-cement sheath surface during radial compression. The results indicate that the peridynamic simulation of damage at the double-layer casing-cement sheath interface under non-uniform loading is in strong agreement with the DIC strain measurements. From the perspective of strain accumulation and damage morphology, increasing the outer casing radius enhances the overall structural stiffness. Strain accumulation at the inner casing-cement interface accelerates, with damage concentrated at the interface. while damage within the cement sheath primarily propagates along the 90° and 270° loading directions. In contrast, an increase radius of the inner casing reduces the constraint on the cement sheath, making the casing more prone to “ovalization” deformation. This extension of the stress transfer path slows strain accumulation at the inner casing–cement interface, with damage propagating along the 0°, 90°, 180°, and 270° directions. Experimental results further indicate that the load-bearing capacity of the model with an inner casing is at least 2.5 times higher than that of the model without an inner casing. The study reveals the mechanical mechanism governing the sealing capacity of the cement sheath in double-layer casings, providing significant theoretical and engineering implications for ensuring wellbore integrity and stability in oil and gas operations.

在超深钻井作业中，经常会遇到蠕变泥岩和高压盐层等地层，这些地层会产生不均匀载荷，对套管设计和井筒完整性构成严重挑战。水泥环与套管之间的界面粘合行为是决定井筒长期完整性的关键因素。基于周动力理论，建立了非均匀载荷作用下双层套管-水泥环界面损伤模型。该模型对非均匀应力作用下界面损伤的演化机制进行了数值表征。使用数字图像相关（DIC）系统进行了实验室测试，以捕获径向压缩过程中套管-水泥环表面的应变演变。结果表明，非均匀载荷作用下双层套管-水泥环界面损伤的周动力模拟结果与DIC应变测量结果吻合较好。从应变积累和损伤形态的角度来看，增大外套管半径可以提高整体结构刚度。内套管-水泥界面应变积累加速，损伤集中在界面处。而水泥环内的损伤主要沿90°和270°加载方向传播。相反，内套管半径的增加减少了对水泥环的约束，使套管更容易发生“卵化”变形。这种应力传递路径的延伸减缓了内套管-水泥界面的应变积累，损伤沿0°、90°、180°和270°方向传播。实验结果进一步表明，加内壳模型的承载能力比不加内壳模型的承载能力至少提高2.5倍。该研究揭示了双层套管中控制水泥环密封能力的机械机制，为确保油气作业中的井筒完整性和稳定性提供了重要的理论和工程意义。

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引用次数: 0

Comparative tests on the failure characteristics and mechanisms of soft inclined foundation waste dump under gravity 重力作用下软倾斜地基排土场破坏特征及机理对比试验

IF 3.7 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-18 DOI: 10.1016/j.gete.2025.100746

Qiang Wen , Shuwei Sun , Jiachen Zhang , Yuan Li , Hui Ding

Landslide disasters occur frequently on the slopes of open-pit mine waste dumps, thus the study of their failure mechanism is crucial to mine environmental protection and safe production. This study conducted three sets of base friction model tests on waste dumps with different inclination angles. Based on an updated speckle analysis and point-tracking technology, the failure process of the waste dump slopes was obtained, focusing on analyzing the occurrence mechanism, failure mode, and stability of the slopes. The findings indicated that the waste dump slopes of inclined foundations have prominent progressive failure characteristics, and due to the influence of the inclined foundation, the waste dump slope failure mode is significantly different. According to the movement characteristics of the slopes in the tests, the deformation process of slopes was categorized into three phases: the uniform deformation phase, the local failure phase, and the overall instability phase. Taking the characteristic moment of the model entering into local failure and overall instability as the stability evaluation index, which showed that anti-inclined foundation slopes had the best stability, followed by horizontal, with down-inclined slopes being the least stable, which is basically consistent with other results. The sliding surface geometry and factor of safety of the slopes were obtained by using the strength reduction method in the FLAC3D software. The deformation characteristics of waste dump slopes with soft inclined foundations derived from numerical modeling are in basic accordance with previous base friction model test results. The study also noted that as the inclination angle of the basement changes, the sliding surface of different types of foundation waste dumps gradually changes from polyline to arc-shaped. These findings could offer qualitative insights into assessing the stability of waste dump slopes on soft inclined foundations, which are of great significance to mine environmental protection and mine safety production.

露天矿排土场边坡滑坡灾害频繁发生，研究其破坏机理对矿山环境保护和安全生产具有重要意义。本文对不同倾角的排土场进行了三组基础摩擦模型试验。基于更新的散斑分析和点跟踪技术，获得了排土场边坡的破坏过程，重点分析了边坡的发生机制、破坏模式和稳定性。研究结果表明：倾斜基础的排土场边坡具有明显的递进破坏特征，且受倾斜基础的影响，排土场边坡破坏模式存在显著差异。根据试验边坡的运动特征，将边坡的变形过程分为均匀变形阶段、局部破坏阶段和整体失稳阶段三个阶段。以模型进入局部破坏和整体失稳的特征矩为稳定性评价指标，表明抗倾斜地基边坡稳定性最好，水平边坡次之，下倾斜地基边坡稳定性最差，与其他结果基本一致。在FLAC3D软件中采用强度折减法得到边坡的滑动面几何形状和安全系数。数值模拟得出的软倾斜地基排土场边坡变形特征与前人基础摩擦模型试验结果基本一致。研究还发现，随着基底倾角的变化，不同类型的基础排土场的滑动面逐渐由多线形变为弧形。研究结果可为软倾斜基础上排土场边坡稳定性评价提供定性认识，对矿山环境保护和矿山安全生产具有重要意义。

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引用次数: 0

Predicting subsurface thermal conductivity from wellbore temperatures 根据井筒温度预测地下导热系数

IF 3.7 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-18 DOI: 10.1016/j.gete.2025.100745

Josiane Jello , Patrick Harsono , Tugce Baser

This study focuses on the prediction of subsurface thermal conductivity using in-situ wellbore temperature profiles by solving an inverse one-dimensional heat equation. Existing methods to measure or estimate thermal conductivity either require core samples, empirical correlations, or are only applicable to shallow depths. To demonstrate how thermal conductivity can be accurately predicted from borehole temperature data collected using a fiber-optic distributed temperature sensing (DTS) system, a field-scale heat injection experiment was performed in an open oil well located near Fairfield, Illinois. The heat equation was solved numerically based on the finite difference method and it was used to predict wellbore temperatures. An optimization technique was introduced into the finite difference model to predict the thermal diffusivity, which was then used to predict the thermal conductivity as these two properties are proportional. A thermal conductivity profile which is consistent with the anticipated thermal properties of the geological strata is obtained and the results from the analyses showed that the thermal conductivity values varied between 0.42 and 5.36 W/m.K. The highest mean square error (MSE) recorded was relatively small with a value of less than 0.005℃. The model presented in this study can widely be used with DTS measurements to predict the subsurface thermal conductivity. This model presents a useful tool to better characterize thermal properties for the design of efficient geothermal systems when the evolution of wellbore temperatures is known.

本研究的重点是通过求解一维逆热方程，利用原位井筒温度剖面预测地下导热系数。现有的测量或估计热导率的方法要么需要岩心样品，要么需要经验相关性，要么只适用于较浅的深度。为了演示如何利用光纤分布式温度传感（DTS）系统收集的井温数据准确预测热导率，在伊利诺伊州费尔菲尔德附近的一口露天油井中进行了现场规模的热注入实验。基于有限差分法对热方程进行数值求解，并将其应用于井筒温度预测。在有限差分模型中引入最优化技术来预测热扩散系数，并将其用于预测导热系数，因为两者是成比例的。得到了与预期地层热物性相符的热导率剖面，分析结果表明，热导率值在0.42 ~ 5.36 W/m.K之间。记录的最高均方误差（MSE）较小，小于0.005℃。本研究提出的模型可以广泛地与DTS测量相结合来预测地下热导率。当井筒温度的变化已知时，该模型提供了一个有用的工具，可以更好地表征热特性，从而设计高效的地热系统。

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引用次数: 0

Thermomechanical analysis method for energy piles with skin friction softening and hardening behavior 具有皮摩软化硬化特性的能源桩热力学分析方法

IF 3.7 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-17 DOI: 10.1016/j.gete.2025.100744

Huaibo Song , Huafu Pei , Hao Wang

Various approaches have been proposed to analyze the thermomechanical behavior of individual energy piles. Although these approaches can account for pile-soil interactions, there is a lack of approaches for continuously describing the full nonlinear range of the load-transfer curve for individual energy piles under thermomechanical loading, including both skin friction softening and the hardening behavior. Therefore, this study developed an analysis method for individual energy piles by considering skin friction softening and hardening behaviors. The developed approach was verified by comparing the simulation results with those of three well-documented field tests, alongside laboratory and centrifuge model tests. The simulation results show a maximum percentage error between the simulation results and the field measurement results is 8.8 %, which is much smaller than that of other methods, indicating a relatively high degree of consistency between the simulation and the actual situation. Besides，the results suggest that the proposed method can capture the full nonlinear range of the load-transfer curve and essential aspects of the pile in terms of the stress and displacement induced by the thermomechanical operation. Finally, a parametric analysis was conducted to study the effects of the model parameters on the energy pile thermomechanical performance. Results show that increasing the dimensionless parameter changes the pile axial thermal stress and displacement oppositely; increasing the residual ratio boosts axial thermal stress, reduces displacements and stress, and moves the neutral point (NP) towards the pile head.

人们提出了各种方法来分析单个能量桩的热力学行为。虽然这些方法可以解释桩-土相互作用，但缺乏连续描述单个能量桩在热力载荷作用下的荷载传递曲线的全部非线性范围的方法，包括皮摩擦软化和硬化行为。因此，本研究提出了考虑皮摩软化和硬化行为的单个能源桩分析方法。通过将模拟结果与三次有充分记录的现场试验以及实验室和离心机模型试验的结果进行比较，验证了所制定的方法。模拟结果表明，模拟结果与现场测量结果的最大误差百分比为8.8 %，远小于其他方法的误差百分比，表明模拟结果与实际情况的一致性较高。研究结果表明，该方法可以捕捉到荷载传递曲线的全部非线性范围，以及热力学作用引起的应力和位移的本质方面。最后，通过参数分析研究了模型参数对能量桩热力学性能的影响。结果表明：增大无量纲参数对桩的轴向热应力和位移产生相反的影响；增加残余比增大轴向热应力，减小位移和应力，使中性点向桩顶移动。

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引用次数: 0

Numerical study on enhancing coalbed methane recovery using stress relief by multiple cavities 多空腔应力释放提高煤层气采收率的数值研究

IF 3.7 2区工程技术 Q3 ENERGY & FUELS

Geomechanics for Energy and the Environment

Pub Date : 2025-09-15 DOI: 10.1016/j.gete.2025.100742

Yi Chen, Lei Zhou, Liulin Fang, Yu Peng, Xiaocheng Li

Conventional horizontal well direct fracturing technology is inadequate for deep coalbed methane (DCBM) surface extraction. The extraction of DCBM presents a technical obstacle that impedes the advancement of China's CBM industry. This study explores the potential of a novel approach involving horizontal wells with multi-cavities to enhance DCBM extraction. A three-dimensional numerical tool, based on the elastic-plastic damage model and material point method (MPM), was developed to examine permeability enhancement and CBM desorption induced by cavities. Systematic engineering simulations were conducted to validate the effectiveness of DCBM extraction. The findings are as follows: 1) The three-dimensional numerical tool accurately simulates large deformation, large displacement, and inner boundary self-contact issues during cavity-induced collapse in deep coal. 2) A single cavity contributes an effective stress-relief volume 23.95 times greater than the cavity volume; permeability increases by 5–800 times in the plastic zones and by 1–5 times in the elastic zones over the initial permeability, and a total CBM desorption of 197.22 m³ is achieved. 3) The DCBM production volume enhanced by horizontal wells with multi-cavities is 24.98 times greater than hydraulic fracturing, with an average production exceeding 10,000 m³ /d and remaining above 6000 m³ /d after one year of extraction. 4) Optimal performance of horizontal wells with multi-cavities can be achieved by reducing the cavity angle and spacing while increasing the cavity width and length. Based on these results, implementing compound fracturing in horizontal wells with multi-cavities is recommended. This study provides a numerical tool and new insights for enhancing DCBM extraction.

常规水平井直接压裂技术在深部煤层气地面开采中存在一定的不足。DCBM的开采是制约中国煤层气产业发展的技术障碍。本研究探索了一种涉及多空腔水平井的新方法的潜力，以提高DCBM的提取。基于弹塑性损伤模型和材料点法（MPM），建立了三维数值工具，研究了空腔对煤层气的增渗和解吸作用。通过系统工程仿真验证了DCBM提取的有效性。研究结果表明：1)三维数值工具准确模拟了深部煤层空腔塌陷过程中的大变形、大位移和内边界自接触问题。2)单个空腔对有效应力消除体积的贡献是空腔体积的23.95倍；与初始渗透率相比，塑性区渗透率增加5 ~ 800倍，弹性区渗透率增加1 ~ 5倍，煤层气总解吸量为197.22 m³ 。3)多腔水平井提高DCBM产量是水力压裂的24.98倍，平均产量超过10000 m³ /d，开采1年后仍保持在6000 m³ /d以上。4)通过减小空腔角度和间距，增大空腔宽度和长度，实现多空腔水平井的最佳性能。在此基础上，建议在多空腔水平井中实施复合压裂。该研究为加强DCBM提取提供了数值工具和新的见解。

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引用次数: 0