{"title":"基于能量演化的含水层页岩破坏特征及评价指标研究","authors":"Xian-yin Qi, Dian-dong Geng, Meng-yao Feng, Ming-zhe Xu","doi":"10.1007/s11440-024-02263-6","DOIUrl":null,"url":null,"abstract":"<div><p>The presence of abundant clay components and microporous structure in shale results in its high hydrophilicity, making a water-rich environment inevitable in petroleum exploration projects. Therefore, it is crucial to consider the influence of bedding structure, moisture content, confining pressure, and their combined effects on the geomechanical properties of shale. This article aims to investigate the mechanical properties of deep shale under varying water content conditions, elucidate the failure mode and failure mechanism of shale in actual engineering scenarios, and explores the interplay between stress, structure, moisture content, and other factors on its mechanical properties. The evaluation of wellbore stability and fracture propagation effects is proposed based on laboratory experiments using triaxial stress and strain data, along with the application of energy evolution theory. The experimental procedures encompass an analysis of shale's microscopic components and structure, as well as anisotropic shale triaxial compression tests conducted under different moisture contents and confining pressures. The results demonstrate that shale exhibits dense pores in its microstructure and displays pronounced anisotropic characteristics in its macrostructure. The presence of water within these pores, combined with the in situ stress within the formation, significantly influences the mechanical properties of shale. This anisotropy decreases with increasing moisture content, but the mechanical performance still decreases. Under triaxial compression conditions, the increase in confining pressure to some extent enhances the anisotropy of shale's deformation characteristics, which is related to the failure modes of shale. However, the detrimental effect of moisture content on shale's mechanical properties still persists. In order to quantify the impact of these factors, this study utilizes the elastic modulus as an indicator of the coupling effect. It combines the triaxial strain curve obtained from laboratory tests and proposes an evaluation index for shale mechanical properties based on the energy evolution theory. This index is suitable for assessing wellbore stability (the stability index called <i>SI</i><sub><i>r</i></sub>) and crack expansion (the brittleness index called <i>BI</i><sub>r</sub>). The calculation results reveal that, during the wellbore drilling process, excavating parallel to the direction of shale bedding while maintaining low moisture content and high confining pressure yields a higher <i>SI</i><sub><i>r</i></sub> value, indicating better wellbore stability. On the other hand, during reservoir fracturing, fracturing perpendicular to the shale bedding direction and maintaining low confining pressure and moisture content result in a smaller <i>BI</i><sub>r</sub> value. This approach is more beneficial for the expansion of shale fracture network in engineering.</p></div>","PeriodicalId":49308,"journal":{"name":"Acta Geotechnica","volume":null,"pages":null},"PeriodicalIF":5.6000,"publicationDate":"2024-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s11440-024-02263-6.pdf","citationCount":"0","resultStr":"{\"title\":\"Study on failure characteristics and evaluation index of aquifer shale based on energy evolution\",\"authors\":\"Xian-yin Qi, Dian-dong Geng, Meng-yao Feng, Ming-zhe Xu\",\"doi\":\"10.1007/s11440-024-02263-6\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>The presence of abundant clay components and microporous structure in shale results in its high hydrophilicity, making a water-rich environment inevitable in petroleum exploration projects. Therefore, it is crucial to consider the influence of bedding structure, moisture content, confining pressure, and their combined effects on the geomechanical properties of shale. This article aims to investigate the mechanical properties of deep shale under varying water content conditions, elucidate the failure mode and failure mechanism of shale in actual engineering scenarios, and explores the interplay between stress, structure, moisture content, and other factors on its mechanical properties. The evaluation of wellbore stability and fracture propagation effects is proposed based on laboratory experiments using triaxial stress and strain data, along with the application of energy evolution theory. The experimental procedures encompass an analysis of shale's microscopic components and structure, as well as anisotropic shale triaxial compression tests conducted under different moisture contents and confining pressures. The results demonstrate that shale exhibits dense pores in its microstructure and displays pronounced anisotropic characteristics in its macrostructure. The presence of water within these pores, combined with the in situ stress within the formation, significantly influences the mechanical properties of shale. This anisotropy decreases with increasing moisture content, but the mechanical performance still decreases. Under triaxial compression conditions, the increase in confining pressure to some extent enhances the anisotropy of shale's deformation characteristics, which is related to the failure modes of shale. However, the detrimental effect of moisture content on shale's mechanical properties still persists. In order to quantify the impact of these factors, this study utilizes the elastic modulus as an indicator of the coupling effect. It combines the triaxial strain curve obtained from laboratory tests and proposes an evaluation index for shale mechanical properties based on the energy evolution theory. This index is suitable for assessing wellbore stability (the stability index called <i>SI</i><sub><i>r</i></sub>) and crack expansion (the brittleness index called <i>BI</i><sub>r</sub>). The calculation results reveal that, during the wellbore drilling process, excavating parallel to the direction of shale bedding while maintaining low moisture content and high confining pressure yields a higher <i>SI</i><sub><i>r</i></sub> value, indicating better wellbore stability. On the other hand, during reservoir fracturing, fracturing perpendicular to the shale bedding direction and maintaining low confining pressure and moisture content result in a smaller <i>BI</i><sub>r</sub> value. 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引用次数: 0
摘要
页岩中含有丰富的粘土成分和微孔结构,因此亲水性很强,在石油勘探项目中,富水环境是不可避免的。因此,考虑垫层结构、含水率、约束压力及其综合效应对页岩地质力学性能的影响至关重要。本文旨在研究不同含水率条件下深层页岩的力学性能,阐明页岩在实际工程场景中的破坏模式和破坏机理,探讨应力、结构、含水率等因素对其力学性能的相互影响。利用三轴应力和应变数据进行实验室实验,并应用能量演化理论,提出了井筒稳定性和裂缝扩展效应的评估方法。实验程序包括分析页岩的微观成分和结构,以及在不同含水量和约束压力下进行的各向异性页岩三轴压缩试验。结果表明,页岩的微观结构中存在致密的孔隙,其宏观结构具有明显的各向异性特征。这些孔隙中水分的存在,加上地层中的原位应力,对页岩的机械特性产生了重大影响。这种各向异性会随着含水量的增加而减弱,但机械性能仍会下降。在三轴压缩条件下,约束压力的增加在一定程度上增强了页岩变形特征的各向异性,这与页岩的破坏模式有关。然而,含水量对页岩力学性能的不利影响依然存在。为了量化这些因素的影响,本研究利用弹性模量作为耦合效应的指标。它结合实验室测试获得的三轴应变曲线,提出了基于能量演化理论的页岩力学性能评价指标。该指数适用于评估井筒稳定性(稳定性指数 SIr)和裂缝扩展性(脆性指数 BIr)。计算结果表明,在井筒钻进过程中,在保持低含水率和高约束压力的情况下,平行于页岩垫层方向开挖可获得较高的 SIr 值,表明井筒稳定性较好。另一方面,在储层压裂过程中,垂直于页岩垫层方向进行压裂,并保持较低的封闭压力和含水量,会产生较小的 BIr 值。这种方法更有利于工程中页岩裂缝网络的扩展。
Study on failure characteristics and evaluation index of aquifer shale based on energy evolution
The presence of abundant clay components and microporous structure in shale results in its high hydrophilicity, making a water-rich environment inevitable in petroleum exploration projects. Therefore, it is crucial to consider the influence of bedding structure, moisture content, confining pressure, and their combined effects on the geomechanical properties of shale. This article aims to investigate the mechanical properties of deep shale under varying water content conditions, elucidate the failure mode and failure mechanism of shale in actual engineering scenarios, and explores the interplay between stress, structure, moisture content, and other factors on its mechanical properties. The evaluation of wellbore stability and fracture propagation effects is proposed based on laboratory experiments using triaxial stress and strain data, along with the application of energy evolution theory. The experimental procedures encompass an analysis of shale's microscopic components and structure, as well as anisotropic shale triaxial compression tests conducted under different moisture contents and confining pressures. The results demonstrate that shale exhibits dense pores in its microstructure and displays pronounced anisotropic characteristics in its macrostructure. The presence of water within these pores, combined with the in situ stress within the formation, significantly influences the mechanical properties of shale. This anisotropy decreases with increasing moisture content, but the mechanical performance still decreases. Under triaxial compression conditions, the increase in confining pressure to some extent enhances the anisotropy of shale's deformation characteristics, which is related to the failure modes of shale. However, the detrimental effect of moisture content on shale's mechanical properties still persists. In order to quantify the impact of these factors, this study utilizes the elastic modulus as an indicator of the coupling effect. It combines the triaxial strain curve obtained from laboratory tests and proposes an evaluation index for shale mechanical properties based on the energy evolution theory. This index is suitable for assessing wellbore stability (the stability index called SIr) and crack expansion (the brittleness index called BIr). The calculation results reveal that, during the wellbore drilling process, excavating parallel to the direction of shale bedding while maintaining low moisture content and high confining pressure yields a higher SIr value, indicating better wellbore stability. On the other hand, during reservoir fracturing, fracturing perpendicular to the shale bedding direction and maintaining low confining pressure and moisture content result in a smaller BIr value. This approach is more beneficial for the expansion of shale fracture network in engineering.
期刊介绍:
Acta Geotechnica is an international journal devoted to the publication and dissemination of basic and applied research in geoengineering – an interdisciplinary field dealing with geomaterials such as soils and rocks. Coverage emphasizes the interplay between geomechanical models and their engineering applications. The journal presents original research papers on fundamental concepts in geomechanics and their novel applications in geoengineering based on experimental, analytical and/or numerical approaches. The main purpose of the journal is to foster understanding of the fundamental mechanisms behind the phenomena and processes in geomaterials, from kilometer-scale problems as they occur in geoscience, and down to the nano-scale, with their potential impact on geoengineering. The journal strives to report and archive progress in the field in a timely manner, presenting research papers, review articles, short notes and letters to the editors.