循环加卸载过程中的水化页岩渗透特性  

Permeability of hydrated shale rocks under cyclic loading and unloading conditions

作　　者：刘先珊[1,2] 潘玉华 李满 康治勇 周虎 乔士豪 LIU Xianshan;PAN Yuhua;LI Man;KANG Zhiyong;ZHOU Hu;QIAO Shihao(Key Laboratory of New Technology for Construction of Cities in Mountain Area,Ministry of Education,Chongqing University,Chongqing 400045,China;School of Civil Engineering,Chongqing University,Chongqing 400045,China)

机构地区：[1]重庆大学山地城镇建设与新技术教育部重点实验室,重庆400045 [2]重庆大学土木工程学院,重庆400045

出　　处：《煤炭学报》2022年第S01期103-114,共12页Journal of China Coal Society

基　　金：国家自然科学基金资助项目(52279094);广西重点研发计划资助项目(桂科AB20238036);中央高校基本科研业务费专项资金资助项目(2020CDCGJ021)

摘　　要：页岩气开发过程中,储层页岩的水化效应突出,其力学特性及渗透特性的演化规律不明确,准确把握其过程中的水化页岩水力学特性尤为关键。以不同水化天数的储层页岩为研究对象,分析水化作用后的页岩力学特性,深入研究循环加卸载过程中的水化页岩渗透性。试验结果表明:单一加载时,水化时间越多的页岩峰值强度越低,渗透率越大,并结合损伤理论建立页岩渗透率与结构损伤的关联性。分析初始加卸载过程中的页岩渗透特性,显示加载渗透率随围压增大而减小,卸载渗透率随围压减小而增大,且同围压下的加载渗透率大于卸载渗透率,阐明损伤的不可逆变形导致页岩加、卸载渗透率的显著差异。通过试验数据的拟合显示:初始加载的页岩渗透率与围压成负指数关系,随循环加载次数增多而变为幂函数关系,说明循环围压加载导致渗透特性变化大而形成不同的渗透率演化模型,卸载渗透率变化则较平缓,与围压均呈幂函数关系。进一步分析5次循环加卸载中的页岩渗透率损伤率及恢复率,均随循环加载次数的增加而降低。最后,通过页岩渗透率对围压敏感因子的变化规律,阐明初始加卸载的渗透率对围压的敏感性最大,随着循环次数的增加,其敏感因子逐渐减小,且低围压的加载渗透率对围压变化较敏感,随围压的增大而减小,而卸载后的应力敏感因子仍保持较小,验证了页岩渗透率演化的损伤性及恢复性,揭示循环加卸载过程中的水化页岩渗透性演化机理。The hydration of reservoir shale is obvious during shale gas extraction,resulting in some vague permeability evolution and mechanical characteristics.Thus the understanding on the hydraulic characteristics of shale during the shale gas extraction process is very important.Taking the reservoir shales under different hydrated days as a case study,the mechanical properties and permeability evolution under cyclic loading and unloading conditions have been investigated.According to the experiments results of the hydrated shale under loading condition,the peak strength is lower and the corresponding permeability is higher for multi-day hydration.Then,the damage theory is applied to analyze the shale permeability evolution resulted in by rock damage.Also,from the permeability variation under initial loading and unloading conditions,the permeability while loading decreases with the increase of confining pressure,however,it increases while unloading with the decrease of confining pressure,and the former is greater than the latter under same confining pressure,indicating that the irreversible deformation causes marked difference of the permeability in the process.In addition,the fitting curves based on the experimental data firstly show the negative exponential relationship between the permeability and confining pressure under initial cyclic conditions and the power function for more cyclic processes,changing the permeability evolution into different fitting model,however,the permeability variation while unloading is in accordance with a power function.Furthermore,the loss ratio and recovery ratio under five cyclic loading and unloading conditions have been analyzed showing a permeability decreasing with more cyclic processes.Finally,the permeability-stress sensitive coefficient has been investigated demonstrating the coefficient is more sensitive to the initial confining pressure and decreases with more cyclic processes.Especially it is more sensitive to lower confining pressure while loading and maintains lower while unl

关 键 词：储层页岩 水化作用 循环加卸载 渗透性 应力敏感因子 

分 类 号：TE311[石油与天然气工程—油气田开发工程]