基于CT试验的黔北凤冈地区牛蹄塘组含方解石脉页岩的力学行为研究

doi:10.13745/j.esf.sf.2024.6.15

地学前缘 ›› 2024, Vol. 31 ›› Issue (5): 117-129.DOI: 10.13745/j.esf.sf.2024.6.15

基于CT试验的黔北凤冈地区牛蹄塘组含方解石脉页岩的力学行为研究

邬忠虎¹(), 孟祥瑞¹, 蓝宝锋²^,³, 刘敬寿⁴^,⁵^,⁶, 巩磊⁷^,⁸, 杨玉翰¹

1.贵州大学土木工程学院, 贵州贵阳 550025
2.贵州大学资源与环境工程学院, 贵州贵阳 550025
3.贵州能源产业研究院有限公司, 贵州贵阳 550025
4.中国地质大学(武汉) 构造与油气资源教育部重点实验室, 湖北武汉 430074
5.中国地质大学(武汉) 资源学院, 湖北武汉 430074
6.中国地质科学院地质研究所自然资源部深部地球动力学重点实验室, 北京 100037
7.东北石油大学环渤海能源研究院, 河北秦皇岛 066004
8.东北石油大学地球科学学院, 黑龙江大庆 163318

收稿日期:2023-11-15 修回日期:2024-04-18 出版日期:2024-09-25 发布日期:2024-10-11
作者简介:邬忠虎(1989—),男,博士,教授,主要从事岩土体破裂失稳、储层裂缝预测及隧道与地下工程灾害防治的研究工作。E-mail: wuzhonghugzu@163.com
基金资助:
国家自然科学基金项目“黔北下寒武统页岩多期裂缝形成机理及分布预测模型研究”(52104080);贵州省科技计划项目“贵州省页岩气效益开发关键技术及工程试验”(黔科合战略找矿[2022]ZD005);贵州省优秀青年科技人才项目(YQK[2023]012)

Mechanical behavior of calcite vein-bearing shale of the Niutitang Formation in Fenggang area, northern Guizhou based on CT tests

WU Zhonghu¹(), MENG Xiangrui¹, LAN Baofeng²^,³, LIU Jingshou⁴^,⁵^,⁶, GONG Lei⁷^,⁸, YANG Yuhan¹

1. College of Civil Engineering, Guizhou University, Guiyang 550025, China
2. College of Resources and Environmental Engineering, Guizhou University, Guiyang 550025,China
3. Guizhou Energy Industry Research Institute Co., Ltd, Guiyang 550025, China
4. MOE Key Laboratory of Tectonics and Petroleum Resources, China University of Geosciences (Wuhan), Wuhan 430074, China
5. School of Earth Resources, China University of Geosciences (Wuhan), Wuhan 430074, China
6. Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
7. Bohai Rim Energy Research Institute, Northeast Petroleum University, Qinhuangdao 066004, China
8. School of Earth Sciences, Northeast Petroleum University, Daqing 163318, China

Received:2023-11-15 Revised:2024-04-18 Online:2024-09-25 Published:2024-10-11

摘要/Abstract

摘要：

通过黔北地区牛蹄塘组页岩的岩心观察显示,方解石脉作为天然裂缝的充填物,并在很大程度上影响着页岩的破坏模式,研究含方解石脉页岩的破坏特性对水力压裂过程中裂缝的起裂、扩展行为的预测与工程设计有重要意义。为揭示方解石脉对页岩力学特性和破裂特征的影响,进行0°、15°、30°、45°、60°、75°和90°7种倾角的单轴压缩和声发射试验,并结合CT扫描技术、有限元计算,构建了三维细观数值模型,讨论不同角度方解石脉对页岩的细观破坏过程和力学性能的影响,分析页岩微裂纹的时空演化规律。结果表明:(1)不同方解石脉角度页岩的声发射和应力-应变曲线形态变化基本相同,均经历压密阶段、弹性阶段、屈服阶段和峰后破坏阶段等4个阶段,各阶段区分明显,特征强度的变化曲线整体呈“U”形,变化程度不断加快,θ为75°时为最低值;(2)方解石脉显著影响页岩的破坏模式,随着角度的提高,由劈裂破坏转变为劈裂型剪切破坏再到剪切滑移破坏,最终变为劈裂张拉破坏;(3)重构的三维模型和物理试验的表现较为一致,并且能够观察到页岩内部和表面裂纹扩展与贯通过程,声发射的空间分布反映了不同阶段下的压缩、张拉和剪切破坏的单元类型,从微观角度揭示了含方解石页岩的破裂机制;(4)页岩的宏观力学特征同时受方解石和基质的影响,体现了明显的各向异性特征,方解石角度越高,对滑移导向作用越强,试件的力学性能越弱。

关键词: 页岩, 方解石, 各向异性, 三维重构, 黔北地区

Abstract:

Core observations of shales from the Niutitang Formation in the northern Qianbei region show that calcite veins often act as natural fracture fillers and largely influence the shale damage patterns. The damage characteristics of calcite vein-bearing shales is important for the prediction of fracture initiation and extension behavior during hydraulic fracturing and for the engineering design. In order to reveal the influence of calcite veins on the mechanical properties and fracture characteristics of shale, uniaxial compression and acoustic emission tests are conducted at seven inclination angles of 0° to 90° in 15° increment. Combined with CT scanning technology and finite element calculations, a three-dimensional (3D) microscopic numerical model is constructed. The effects of calcite vein angle on the fine-scale shale damage process as well as shale mechanical properties are discussed, and the spatiotemporal evolution of shale microcracks are analyzed. The results show that (1) under different calcite vein angles the shale acoustic emission and stress-strain curves show similar curve shape changes, in four stages, namely compression-density, elasticity, yielding, and post-peak damage, with obvious distinctions between stages. The change curve of the characteristic intensity is “U”-shaped with a local minimum at θ of 75°. (2) Calcite veins significantly affect the damage mode: As the vein angle decreases, the damage mode changes from cleavage to cleavage-type shear, to shear-slip, and finally to cleavage-tension. (3) The reconstructed 3D model is largely consistent with physical testing data, providing insights into the process of crack expansion and penetration at shale’s interior and surface. The spatial distribution of acoustic emission reflects the compression, tension, and shear damage types at different stages, revealing the fracture mechanism of calcite-containing shale from the microscopic point of view. (4) Calcite and matrix simulatineously and anisotropically affect the macroscopic mechanical properties of shale: The higher the calcite vein angle, the stronger its slip guidance effect, and the weaker the mechanical properties of the specimens.

Key words: shale, calcite, anisotropy, three-dimensional reconstruction, northern Guizhou

中图分类号:

邬忠虎, 孟祥瑞, 蓝宝锋, 刘敬寿, 巩磊, 杨玉翰. 基于CT试验的黔北凤冈地区牛蹄塘组含方解石脉页岩的力学行为研究[J]. 地学前缘, 2024, 31(5): 117-129.

WU Zhonghu, MENG Xiangrui, LAN Baofeng, LIU Jingshou, GONG Lei, YANG Yuhan. Mechanical behavior of calcite vein-bearing shale of the Niutitang Formation in Fenggang area, northern Guizhou based on CT tests[J]. Earth Science Frontiers, 2024, 31(5): 117-129.

图/表 19

图1 FC-1牛蹄塘组岩心观察图(与层理面平行发育的层间缝,被方解石脉充填(左)、高角度的剪切裂缝、揉皱作用形成的张拉裂缝(右))

Fig.1 Core samples from the Niutitang Formation in well FC-1

图2 试样取岩心示意图

Fig.2 Core sampling scheme

图3 含方解石脉页岩样品

Fig.3 Calcite vein-bearing shale samples

图4 试样扫描电镜图片

Fig.4 Microscopic characteristics of shale specimen by SEM

图5 试验系统及声发射传感器布置

Fig.5 Acoustic emission test setup and sensor arrangement

图6 CT扫描获得的页岩图像以及微观结构特征 a—nanoVoxel-3502E系列X射线显微CT系统;b—扫描次数及间隔;c—某一切片的扫描图像;d—c中红色区域的放大图像。

Fig.6 Microstructural characterization of shale by CT scan imaging

图7 扫描线和扫描线上的变化曲线 a—扫描线的位置;b—扫描线上的灰度值变化,并通过3个阈值来区分方解石、石英、页岩和孔洞。

Fig.7 Change of greyscale value at each pixel along the horizontal scanning line

图8 图像的叠加和矢量化转换示意图

Fig.8 Digital core reconstruction through image superposition/vetorization

表1 岩石样品的材料参数

Table 1 Material parameters for rock samples

材料	弹性模量/GPa	抗压强度/MPa	泊松比	拉压比	内摩擦角/(°)
页岩	51.6	145	0.22	14	35
方解石	80.5	101	0.30	11	30
石英	96.0	373	0.08	15	60

图9 构建的方解石脉倾角75°的数值模型 a—CT扫描重建得到的三维模型;b—赋予材料属性后的弹性模量分布和单轴拉伸试验的加载方式。

Fig.9 Digital model of calcite veins with 75° inclination angle

图10 不同方解石脉倾角页岩应力-应变曲线

Fig.10 Stress-strain curves of shale with different calcite vein inclinations

图11 不同方解石脉倾角页岩破坏模式图

Fig.11 Damage patterns of shales with different calcite vein inclinations a—θ=0°;b—θ=15°;c—θ=30°;d—θ=45°;e—θ=60°;f—θ=75°;g—θ=90°。

图12 方解石脉为0°时页岩试样AE事件数、累积事件计数和应力-应变关系

Fig.12 Plot of AE event count, cumulative event count, and stress strain vs. time for shale specimens with calcite vein angle at 0°

图13 不同角度下含方解石脉页岩的单轴压缩声发射及应力应变关系图

Fig.13 Results of uniaxial compression acoustic emission tests for calcite vein-bearing shales with different vein inclinations a—θ=15°;b—θ=30°;c—θ=45°;d—θ=60°;e—θ=75°;f—θ=90°。

图14 特征强度应力变化图

Fig.14 Characteristic of stress variation with vein inclination by physical testing (left) and modeling (right)

图15 方解石脉倾角为60°时试件的断裂演化图 a—元素损伤图;b—应力云图;c—垂向位移图;d—垂向切割图;e—声发射演化图。

Fig.15 3D modeling of fracture evolution in shale specimen with a calcite vein inclination of 60°

图16 方解石脉倾角为45°时试件的应力演化的切片图

Fig.16 2D slice through 3D models showing stress evolution in shale specimen with calcite vein inclination of 45°

图17 应力应变曲线图、元素损伤图和声发射演化图 a—方解石脉倾角为0°试样;b—方解石脉倾角为90°试样。

Fig.17 Stress-strain diagrams, damage evolution models and AE simulation diagrams under calcite vein inclinations of 0° (a) and 90° (b)

图18 模拟试样最终破坏的声发射图

Fig.18 Shale final damage under different vein inclinations by acoustic emission modeling

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基于CT试验的黔北凤冈地区牛蹄塘组含方解石脉页岩的力学行为研究

Mechanical behavior of calcite vein-bearing shale of the Niutitang Formation in Fenggang area, northern Guizhou based on CT tests

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