基于扩展有限元分析的页岩水力压裂裂缝扩展规律探究
投稿时间:2021-09-05  修订日期:2022-02-15  点此下载全文
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作者单位邮编
温继伟 石家庄铁道大学土木工程学院 050043
项天 成都理工大学环境与土木工程学院 610059
朱茂 成都理工大学环境与土木工程学院 610059
胡萍 成都理工大学环境与土木工程学院 
毛建设 中石化中原石油工程有限公司管具公司 
荆羽慧 成都理工大学环境与土木工程学院 
基金项目:四川省科技厅应用基础研究项目“页岩气水力喷射压裂用高效节能型仿生耦合喷嘴研发及定向造缝机理研究(自由探索型)”(编号:2019YJ0506)
中文摘要:水力压裂是开采地下页岩气资源的有效技术手段,探究页岩水力压裂裂缝的扩展规律,可为页岩气的高效开采提供科学的指导依据。通过运用大型有限元软件ABAQUS中的扩展有限元模块,针对不同地应力差工况条件下均质页岩中初始裂缝的位置、方位角、数量和含层理页岩中层理的构造方向、内部倾角、岩性对水力裂缝扩展的影响进行探究。结果表明:对于垂向扩展的水力裂缝,水平主应力增大使裂缝更不易扩展,裂缝扩展长度减小、起裂压力增大;在注液体积流量相同时,向初始裂缝两端同时起裂所形成的水力裂缝长度大于仅向一侧起裂;当初始裂缝处于页岩中部且呈45°方向时,裂缝会向最大水平主应力 方向偏转,且偏转程度随最大水平主应力的增大而增大;分时多簇压裂时,裂缝间的扩展会相互干扰,且会较大的影响裂缝扩展的形态和起裂压力,但对裂缝注液点裂缝宽度影响较小;对于含水平和竖直构造层理的页岩,改变层理内部倾角,水力裂缝会出现不同程度偏转,且其偏转程度随着层理内部倾角的增大而减小;对于含45°方向构造层理的页岩,水力裂缝在层理分别为砂岩、煤岩和泥岩中的偏转程度依次增大,且裂缝偏移比随着最大水平主应力的增大而增大。
中文关键词:页岩气  水力压裂  扩展有限元  地应力差  层理  裂缝扩展规律
 
Exploration of fracture propagation laws of shale hydraulic fracturing based on extended finite element analysis
Abstract:Hydraulic fracturing is an effective technical method to exploit underground shale gas resources. To investigate the law of fracture propagation in shale hydraulic fracturing can provide scientific guidance for high-efficient exploitation of shale gas. By using the extended finite element module of ABAQUS which is a large finite element software to investigate the influence of position, azimuth and number of initial fractures in homogeneous shale, and the structural direction, internal dip angle and lithology of the bedding shale on hydraulic fracture propagation under the different ground stress deviation conditions. The results show that for vertical hydraulic fractures, the increase of horizontal principal stress makes the fracture more difficult to propagate, the fracture propagation length decreases, and the initiation pressure increases. When the volume flow of liquid injection is the same, the length of hydraulic fracture formed by simultaneous initiation at both ends of the initial fracture is larger than that formed only on one side. When the initial fracture is located in the middle of shale with a direction of 45°, the fracture will deflect to the direction of the maximum horizontal principal stress, and the degree of deflection increases with the increase of the maximum horizontal principal stress. In the process of time-sharing multi-cluster fracturing, the propagation of fractures will interfere with each other, and it will greatly affect the morphology of fracture propagation and initiation pressure, but it has little influence on the fracture width at the injection point. For shale with horizontal and vertical bedding structures, hydraulic fracture deflection will be deflected to different degrees when the internal dip angle of bedding is changed, and the deflection degree of hydraulic fractures decreases with the increase of the internal dip angle of bedding. For shale with structural bedding in the direction of 45°, the deflection degree of hydraulic fractures increases successively in sandstone, coal rock and mudstone, and the fracture migration ratio increases with the increase of the maximum horizontal principal stress.
keywords:shale gas  hydraulic fracturing  XFEM  ground stress deviation  bedding  laws of fracture propagation
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