非结构网格数值方法优化水平井多段压裂  

Unstructured Grid Numerical Method to Optimize Horizontal Well with Multiple Fractures

作　　者：郑海军[1] 毛新军[2] 毕全福 胡广文 卢德唐[1] 

机构地区：[1]中国科学技术大学,安徽合肥230027 [2]新疆油田勘探公司,新疆克拉玛依834000 [3]西部钻探工程公司,新疆克拉玛依834000

出　　处：《油气井测试》2015年第4期1-6,75,共6页Well Testing

基　　金：国家重大科技专项"新一代油藏数值模拟软件"(2011ZX05009-006);973项目"二氧化碳减排;春村和资源利用的基础研究"(2011CB707305);中国科学院战略先导科技专项"页岩气勘探开发理论基础与关键技术"(XDB10030402)联合资助

摘　　要：为了克服解析方法和规则网络数值方法中矩形边界和井与边界必须平行的限制,提出了复杂油气储层水平井多段压裂非结构PEBI网络划分方法及有效裂缝半长概念,在此基础上实现了渗流方程的有限体积离散。针对离散后线性方程组具有稀疏性、不规则性、大规模性及非对称性的特点,采用预处理的GMRES进行求解,研发了相应的数值模拟程序。利用该程序对某油田实际井例进行模拟计算。计算表明,水平多段压裂井在井长较长且裂缝较多情况,其流动计算可近似成水平井;当水平井长度一定时,裂缝条数及裂缝半长的增加,累计产量增加,但增加幅度逐渐减少,对渗透率小于2mD储层,裂缝间距80~120m,裂缝有效半长50~80m较为合适,同时水平井与边界（或断层）方位也影响其产量。试采期间,时间对产量影响最大,早期产量较高,之后产量迅速衰减,半年后产量仅为早期的1/5且趋于稳定。因此,水平井多段压裂井实际生产时,早期宜采用高井底压力,保持较小流量,之后逐渐减小井底压力,以保持长时间稳定开采。In order to overcome the limitation that the rectangular boundary must be parallel to the well boundary in the analytical method and regular grid numerical method,agrid division of non-structural PEBI grid for horizontal well with multiple fractures in reservoir is proposed and the effective fracture half-length is defined,and on this basis,the finite volume discretization of seepage equations has been realized.After discretization,the system of linear equations is sparse,irregular and asymmetric with large scale;accordingly,the paper adopts the pretreatment of GMRES for solutions,and develops a numerical simulation program correspondingly.The program is used for simulated calculation of actual examples in a particular oil field.The calculation shows that the flow calculation of horizontal multistage fracturing wells with longer well length and more fractures is approximate to that of horizontal wells;if the length of horizontal wells is fixed,the cumulative output rises with the increase of fracture number and fracture half-length,but the rise gradually decreases.It is suitable for the reservoir whose permeability is less than 2mD,when the fracture interval is 80-120 mand the effective fracture half-length is 50-80m;meanwhile,the orientation of horizontal wells and the boundaries(or faults)also affect the output.During the pilot production,time had the greatest influence on the output.It has high output in the early stage,but later the output decreases quickly.After six months,the output is just 1/5of the early production and tends towards stability.Therefore,during the actual production in multistage fracturing horizontal wells,we should use high bottom-hole pressure in the early period,keeping a small flow,and then gradually reduce the bottom-hole pressure,so as to remain stable exploitation for a long time.

关 键 词：水平井多段压裂 PEBI网格 产能预测 

分 类 号：TE357[石油与天然气工程—油气田开发工程]