摘要
页岩渗透率极低,能作为CO_(2)地质埋存的盖层。CO_(2)-地层流体长期作用下页岩力学性质发生变化,直接影响页岩盖层的密封性。基于此,为研究超临界CO_(2)-盐水长时间作用对页岩拉伸断裂特征影响,采用超临界CO_(2)-盐水在110℃、30 MPa条件下对龙马溪页岩分别饱和15 d和30 d,并开展了超临界CO_(2)-盐水饱和前后页岩巴西劈裂测试。同时,结合声发射(AE)和数字图像相关(DIC)技术实时监测了页岩连续变形及断裂过程。研究结果表明:超临界CO_(2)-盐水作用引起的非均匀损伤易诱导页岩发生多次局部断裂,表现为加载过程中出现大量离散的点状或条带状应变集中区;随着超临界CO_(2)-盐水饱和时间增加,页岩的剪切断裂现象明显增加,断裂模式逐渐由拉伸断裂主导向拉伸-剪切混合断裂转变;超临界CO_(2)-盐水作用增加了页岩裂缝复杂程度,裂缝形态由单一平直裂缝变为弯曲裂缝带;超临界CO_(2)-盐水饱和后页岩中产生溶蚀孔隙和微裂缝、黏土和有机质膨胀等微观结构的变化直接导致拉伸断裂性质发生显著弱化,且饱和时间越长降低幅度越大。与干燥页岩相比,超临界CO_(2)-盐水饱和15 d和30 d的页岩抗拉强度降低40.18%和48.21%,起裂应力降低17.72%和37.99%,损伤应力降低35.54%和58.36%。相关研究成果明确了超临界CO_(2)-盐水长期作用对页岩拉伸断裂性质的弱化规律,可为页岩CO_(2)地质埋存设计提供依据。
Shale has extremely low permeability and could be used as a caprock for CO_(2) geological storage.The mechanical properties of shale change under the CO_(2)-fluid long-term interaction,which directly affects the sealing performance of shale caprock.Based on this,to study the effect of supercritical CO_(2)-brine on the tensile fracture characteristics of shale,supercritical CO_(2)-brine is used to saturate the Longmaxi shale for 15 days and 30 days under the conditions of 110℃and 30 MPa,respectively,and the Brazilian splitting tests are conducted on shale before and after supercritical CO_(2)-brine saturation.Meanwhile,the continuous deformation and fracture process of shale is monitored in real time by combining acoustic emission(AE)and digital image correlation(DIC)techniques.The results show that the non-uniform damage of shale caused by supercritical CO_(2)-brine interaction can easily induce multiple local fractures,which is manifested as a large number of discrete point-like or strip-like strain concentration areas during the loading process.In addition,with the increase of supercritical CO_(2)-brine saturation time,the shear fracture phenomena increase significantly,and the fracture mode gradually changes from tensile fracture to tension-shear mixed fracture.Supercritical CO_(2)-brine interaction increases the complexity of shale fractures,and the fracture morphologies change from a straightly single fracture to a curved fracture band.After supercritical CO_(2)-brine saturation,micro-structural changes such as the generation of dissolution pores and microcracks and expansion of clay and organic matter in shale directly lead to a significant weakening of tensile fracture properties,and the longer the saturation time,the greater the reduction.Compared with the dry shale,the tensile strength of shale saturated with supercritical CO_(2)-brine for 15 days and 30 days decreases by 40.18%and 48.21%,the initiation stresses decrease by 17.72%and 37.99%,and the damage stresses decrease by 35.54%and 58.36%,respectively.The study has clarified the weakening law of the tensile fracture properties of shale under supercritical CO_(2)-brine long-term interaction,which can provide a reference for CO_(2) geological storage.
作者
邱仁怡
张广清
郑学林
罗森林
周大伟
QIU Renyi;ZHANG Guangqing;ZHENG Xuelin;LUO Senlin;ZHOU Dawei(College of Petroleum Engineering,China University of Petroleum-Beijing,Beijing 102249,China;State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum-Beijing,Beijing 102249,China;Research Institute of Petroleum Engineering Technology,Shengli Oilfield Company,SINOPEC,Dongying 257000,China)
出处
《中国矿业》
北大核心
2025年第5期246-256,共11页
China Mining Magazine
基金
中石油战略合作科技专项资助(编号:ZLZX2020-02)
国家自然科学基金青年项目资助(编号:52104050)。
