基于嵌入黏聚单元法的页岩储层压裂缝网扩展规律  

Propagation law of fracture network in shale reservoirs based on the embeded cohesive unit method

作　　者：位云生[1] 林铁军[2] 于浩[2] 齐亚东[1] 王军磊[1] 金亦秋 朱汉卿 WEI Yunsheng;LIN Tiejun;YU Hao;QI Yadong;WANG Junlei;JIN Yiqiu;ZHU Hanqing(PetroChina Research Institute of Petroleum Exploration&Development,Beijing 100083,China;State Key Laboratory of Oil&Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu,Sichuan 610500,China;PetroChina Exploration and Production Company,Beijing 100083,China)

机构地区：[1]中国石油勘探开发研究院 [2]“油气藏地质及开发工程”国家重点实验室·西南石油大学 [3]中国石油勘探与生产分公司

出　　处：《天然气工业》2022年第10期74-83,共10页Natural Gas Industry

基　　金：国家自然科学基金项目“深层页岩多级压裂地应力场时空演化及套管失效机理研究”(编号:52104008)。

摘　　要：页岩储层压裂后形成的裂缝网络是页岩气有效开发的基础和关键,体积压裂过程中,对天然裂缝的发育形态的认识与人工裂缝的控制是压裂改造的关键和难点问题。为此,以四川盆地南部地区奥陶系五峰组—志留系龙马溪组页岩储层为研究对象,基于批量嵌入黏聚单元法(BCZM)以及牵引—分离损伤理论(Traction—Separation Law,TSL)对天然裂缝空间展布及性质进行表征,并建立了富集天然裂缝网群的页岩储层有限元模型,分析了人工裂缝与水平层理、天然裂缝交汇的裂缝网演化规律。研究结果表明:(1)压裂过程中,压裂液会优先沿水平层理与人工主裂缝方向流动,驱使主裂缝不断与天然裂缝进行沟通,最终形成类似星形包络线的压裂改造区域;(2)星形改造区域关于井眼呈现对称分布,随着压裂作业的进行,当有效改造半径达到一定值后,改造区域几何面积趋于稳定;(3)井口压裂液注入排量对压裂缝网形态影响较大,实际施工时应选择合适的注入排量,过小的压裂排量会使地层中液体压力难以打开天然裂缝,而过大的排量又会导致人工水力主裂缝直接穿越天然裂缝而被层理捕获,最终不能形成复杂有效的网状裂缝。结论认为,开展页岩储层压裂缝网演化模拟对认识、预测及控制页岩储层压裂缝网形态具有重要的理论指导意义,将有助力我国深层页岩气开发。Fracture networks formed after fracturing in shale reservoirs are the basis and key to the effective development of shale gas,and the complexity of fracture network morphology determines the final fracturing effect.Hence,it is essential to study the evolution mechanism of the intersection and expansion of artificial hydraulic fractures and the competition of natural fractures in the fracturing process.By taking the Ordovician Wufeng Formation-Silurian Longmaxi Formation shale reservoirs in the southern Sichuan Basin as the research object,the spatial distribution and properties of natural fractures is characterized based on the batched cohesive zone method(BCZM) and the traction-separation law(TSL),and the finite element model is established for shale reservoirs enriched with natural fracture network groups.And the competitive evolution law of the fracture network caused by the intersection of artificial fractures,horizontal bedding and natural fractures is studied,the formation process and morphology distribution of dynamic fracture networks in fracturing process are simulated,and the approximate mathematical formula of regional profile curves of the final fracture network is fitted.Finally,the influence of wellhead fracturing fluid injection rate on fracture network morphology is annalyzed.The results were obtained as follows.(1) During the fracturing process,the fracturing fluid preferentially flows along the direction of horizontal bedding and the artificial principal fracture,which continuously drives major fracture intersects with the natural fracture,and finally forms a fracture zone similar to a star envelope.(2) Star-shaped stimulation zone is symmetrical and its geometric area tends to be constant when effective radius reaches some value.(3) The injection displacement of the wellhead fracturing fluid has a great influence on the shape of the fracturing network.In actual construction,an appropriate injection displacement should be selected.If the displacement is too small,the liquid pressure in the forma

关 键 词：页岩气 储层改造 压裂 黏聚单元 缝网演化 注入排量 层间应力差 星形包络线 扩展规律 

分 类 号：TE377[石油与天然气工程—油气田开发工程]