缝内暂堵转向压裂数值模拟方法  

Numerical simulation of in-fracture temporary plugging and diverting fracturing(ITPDF)

作　　者：王博 刘雄飞 胡佳 刘进军 周福建[2] 周航 WANG Bo;LIU Xiongfei;HU Jia;LIU Jinjun;ZHOU Fujian;ZHOU Hang(College of Petroleum Engineering,China University of Petroleum-Beijing at Karamay,Karamay 834000,China;Unconventional Oil and Gas Institute of Science and Technology,China University of Petroleum-Beijing,Beijing 102249,China;Sinopec Oil&Gas Pipeline Inspection CO.,LTD,Xuzhou 221008,China;PetroChina Xinjiang Oilfield Development Company,Karamay 834000,China)

机构地区：[1]中国石油大学(北京)克拉玛依校区石油学院,克拉玛依834000 [2]中国石油大学(北京)非常规油气科学技术研究院,北京102249 [3]中石化长输油气管道检测有限公司,徐州221008 [4]中国石油新疆油田分公司开发公司,克拉玛依834000

出　　处：《石油科学通报》2021年第2期262-271,共10页Petroleum Science Bulletin

基　　金：中国石油科技创新基金“动态封孔下多簇裂缝竞争扩展规律研究(No.2020D-5007-0207)”;中国石油大学(北京)克拉玛依校区科研启动基金“基于缝内暂堵的重复压裂侧向缝网形成机理研究(No.XQZX20210001)”联合资助。

摘　　要：水力压裂过程中,暂堵剂在缝内形成架桥封堵,提升缝内净压力,转向激活天然裂缝,增大储层改造体积。本文介绍了水力压裂物理过程及基本控制方程,基于该方程建立了二维流固全耦合相交裂缝扩展模型,实现缝内暂堵转向过程的模拟。利用黏结单元指定水力裂缝与天然裂缝扩展路径,基于内聚区模型控制裂缝单元的起裂与扩展。基于达西方程和润滑方程,令流体在暂堵体内流动的压降,与流体在无暂堵体缝内流动的压降相等,通过改变润滑方程中的等效黏度项来模拟暂堵体对缝内流体流动的影响。模型模拟结果与已发表的数值模拟结果吻合,证明了模型的可靠性。基于该模型研究了缝内暂堵转向动态过程,模拟结果表明,流体压力在暂堵体内部迅速降低,缝内净压力及裂缝开度显著增大,转向激活天然裂缝。整个缝内暂堵转向过程分为5个阶段:(1)水力裂缝起裂并扩展至相交点;(2)水力裂缝由相交点扩展至暂堵体;(3)水力裂缝停止扩展及天然裂缝上分支扩展结束;(4)天然裂缝上分支扩展结束至下分支扩展结束;(5)裂缝体积持续膨胀。本文工作为后续系统开展缝内暂堵转向规律研究提供了方法与模型基础。During hydraulic fracturing,the injected self-degradable diverters can bridge and form a tight plug within the hydraulic fractures.The net fracture pressure can be enlarged to a great level and the natural fractures can be activated,thus the stimulated volume is greatly enlarged.The investigation of the in-fracture temporary plugging and diverting fracturing(ITPDF)process is beneficial for uncovering the mechanisms and the patterns of ITPDF.This paper systematically introduces the physical processes and the controlling equations of the hydraulic fracturing problems during ITPDF.A 2D fluid-solid fully-coupled finite element model is developed to simulate the overall fracture propagation when a hydraulic fracture intersects a natural fracture.In the model,cohesive elements are applied to pre-define the fracture propagation paths and a cohesive zone model is applied to control the fracture initiation and propagation criteria.In this way,the calculation of the stress singularity at the fracture tips can be avoided.Moreover,this paper assumes the diffusive term from Darcy’s equation equals the conductivity term in Reynold’s equation,and the equivalent viscosity is modified to model the effects of the tight plug on fluid flow.In this way,it is not necessary to change the governing equation of the fracturing fluid flow within the hydraulic fracture.The simulation results of the developed model are consistent with the reported simulation results at various conditions,which verifies the reliability of the developed model.Further,this paper simulates the dynamic process of ITPDF based on the established model.The simulation results show the fluid pressure declines sharply within the tight plug,and the net fracture pressure and the fracture width are enlarged dramatically,thus the NF(Natural Fracture)is activated.The whole process of ITPDF includes five stages:(1)the hydraulic fracture initiates at the fluid injection point and then propagates and arrives at the intersection point of the hydraulic fracture and the natur

关 键 词：暂堵压裂 相交扩展 封堵模型 动态过程 

分 类 号：TE357.1[石油与天然气工程—油气田开发工程]