页岩弹性模量非均质性对地应力及其损伤的影响  

Study of the influence of elastic modulus heterogeneity on in-situ stress and its damage in gas shale reservoirs

作　　者：汪道兵 葛洪魁[3] 宇波 文东升 周珺[4] 韩东旭 刘露[5] Wang Dao-bing;Ge Hong-kui;Yu Bo;Wen Dong-sheng;Zhou Jun;Han Dong-xu;Liu Lu(School of Mechanical Engineering ,Beijing Key Laboratory of Pipeline Critical Technology and Equipment for Deepwater Oil ＆ Gas Development ,Beijing Institute of Petrochemical Technology ,Beijing 102617 ,China;School of Aeronautic Science and Engineering, Beihang University ,Beijing 100083, China;The Unconventional Natural Gas Institute, China University of Petroleum ,Beijing 102249, China;SINOPEC Research Institute of Petroleum Engineering, Beijing 100101, China;Chongqing Gas Mine of Southwest Oil and Gas Field Branch ,CNPC ,Chongqing 400021 ,China)

机构地区：[1]北京石油化工学院机械工程学院,深水油气管线关键技术与装备北京市重点实验室,北京102617 [2]北京航空航天大学航空科学与工程学院,北京100083 [3]中国石油大学(北京)非常规天然气研究院,北京102249 [4]中国石化石油工程技术研究院,北京100101 [5]中国石油天然气集团公司西南油气田分公司重庆气矿,重庆400021

出　　处：《天然气地球科学》2018年第5期632-643,共12页Natural Gas Geoscience

基　　金：北京市高水平创新团队建设计划项目(编号：IDHT20170507);国家重点基础研究发展计划(973)项目(编号：2015CB250903);中国石油大学(北京)克拉玛依校区科研启动基金(编号：RCYJ2016B-01-001)联合资助

摘　　要：页岩的应力非均质性对钻完井、压裂改造和气藏开发动态等过程具有显著影响,目前未给出合理的表征方法来刻画页岩水力压裂过程中力学非均质性引起的岩石损伤/破裂及"应力阴影"效应。采用Galerkin有限元数值方法,通过COMSOL Multiphysics求解器,利用Matlab脚本语言进行了二次开发;采用Weibull概率密度函数表示页岩力学非均质性,数值模拟了水力压裂过程中流固耦合条件下非均质性对页岩地应力分布、应变能密度、流压和损伤因子等因素的影响规律。当地层完全为均质时,Von-Mises应力、应变能密度和损伤因子递减分布曲线特征明显,随着地层非均质增强,它们的分布曲线呈现起伏波动的规律,且Von-Mises应力、应变能密度与损伤因子相关性较好。据此提出了二维平面应变条件下力学非均质性引起的岩石损伤/破裂及"应力阴影"效应表征方法,即用单点线处的Von-Mises应力或应变能密度刻画岩石的局部破裂程度或应力阴影效应的强弱,用单位面积的平均应变能密度刻画岩石整体的破裂程度或应力阴影效应的强弱。该研究对进一步改进页岩体积压裂设计和提高气井产能具有重要指导意义。Shale heterogeneity has a significant effect on drilling and completions,hydraulic fracturing and hydrocarbon development performance,but it lacks representation of rock damage/failure caused by the mechanical heterogeneity and＂stress shadow＂effect during the hydraulic fracturing process.In this paper,Galerkin finite element method was adopted to numerically simulate the hydro-mechanical coupled interaction based on the solver in the COMSOL Multiphysics software and Matlab scripting development.The Weibull probability density function was used to represent the mechanical heterogeneity of gas shale.Under the condition of fully fluid-solid coupling during the fracking process,the effect of mechanical heterogeneity on von-Mises stress,strain energy density,damage factor and fluid pressure was numerically simulated in the gas shale wells.When the formation is completely homogeneous,their curves of von Mises stress,strain energy density and damage factor along a certain straight line showed obvious decreasing distribution.As the strata are heterogeneously enhanced,their distribution curves showed fluctuations,and von Mises stress and strain energy density respectively had a good relationship with damage factors.Accordingly,the method of rock damage/fracture and＂stress shadow＂effect caused by mechanic heterogeneity was put forward under the condition of 2D plane strain.That was to use,the von Mises stress or strain energy density at the single point or line to characterize the degree of local rupture or the shadow effect of stress,and the average strain energy density per unit area to characterize the degree of rupture of the rock or the intensity of the shadow effect.The study is of great significance to further improve the SRV fracturing design and the productivity of gas shale wells.

关 键 词：韦伯函数 页岩气 损伤力学 非均质性 水力压裂 有限元方法 

分 类 号：TE357.1[石油与天然气工程—油气田开发工程]