水、ScCO2致裂煤体裂纹形态与形成机制研究  

Morphology and formation mechanism of fractures in coal using hydraulic/ScCO2 fracturing

作　　者：李畅 梁卫国[1,2] 侯东升[1,2] 姚宏波 宋晓夏 LI Chang;LIANG Weiguo;HOU Dongsheng;YAO Hongbo;SONG Xiaoxia(College of Mining Engineering,Taiyuan University of Technology,Taiyuan,Shanxi 030024,China;Key Laboratory of In-situProperty-improving for Mining of Ministry of Education,Taiyuan University of Technology,Taiyuan,Shanxi 030024,China)

机构地区：[1]太原理工大学矿业工程学院,山西太原030024 [2]太原理工大学原位改性采矿教育部重点实验室,山西太原030024

出　　处：《岩石力学与工程学报》2020年第4期761-772,共12页Chinese Journal of Rock Mechanics and Engineering

基　　金：国家自然科学基金资助项目(51874206);山西省科技重大专项(MQ2016-01)。

摘　　要：为研究不同压裂条件下致裂煤体裂纹形态与形成机制,采用无烟煤试件在轴压/围压分别为12/10,14/10和16/10MPa下开展水力、ScCO2压裂试验,综合运用显微CT和三维形貌扫描表征压裂后裂隙煤体的内部裂纹形态、裂纹面粗糙度特征,并讨论不同压裂条件下致裂煤体裂纹的起裂扩展机制。结果表明:ScCO2压裂形成的裂纹数目更大、分叉更多、开度更小、裂纹面曲折度更高,显微CT得到的孔裂隙率表明ScCO2压裂改造范围大于水力压裂;与水力压裂不同,ScCO2压裂影响范围更大、释放的能量更多,导致裂纹网络趋于一次形成;水、ScCO2压裂裂纹起裂扩展均受地应力状态、层理弱面的影响,只有垂向地应力差异系数大于0.6,才能产生纵向主裂纹,反之,产生横向主裂纹;采用最大拉应力理论能较好预测产生纵向裂纹的临界起裂压力,而基于莫尔–库仑理论推导的起裂准则,能较好预测水、ScCO2致裂煤体下产生横向裂纹的临界起裂压力,相对误差在5%以内。In order to study the morphology and formation mechanism of fractures in coal induced by hydraulic fracturing under different conditions,water/ScCO2 fracturing tests were carried out on anthracite specimens under axial/confining pressures of 12/10,14/10 and 16/10 MPa,respectively. The micro-CT and three-dimensional shape scanning were used to characterize the internal fracture morphology and fracture surface roughness of fractured samples,and the fracture initiation and propagation mechanisms with different fracturing conditions were discussed. The results show that ScCO2 fracturing forms a larger number of fractures with more bifurcation,smaller opening and higher fracture tortuosity. The pore fracture rate obtained by micro-CT indicates that,compared with hydraulic fracturing,the transformation range of ScCO2 fracturing is larger and ScCO2 fracturing releases more energy,resulting in a fracture network tending to form once. Fracture initiation and propagation resulted from water/ScCO2 fracturing are affected by the geo-stress state and the bedding or weak surface. Only in the case that the vertical ground stress difference coefficient is greater than 0.6,vertical fracture can be produced,otherwise transverse fracture occurs. The maximum tensile stress theory can better predict the critical initiation pressure of longitudinal fractures,while the initiation criterion based on Mohr-Coulomb theory can better predict the critical initiation pressure of transverse fractures induced by water and ScCO2 fracturing with a relative error within 5%.

关 键 词：采矿工程 水力压裂 ScCO2压裂 起裂压力 裂纹形态 莫尔–库仑理论 

分 类 号：TD32[矿业工程—矿井建设]