基于THMD多场耦合的地热断层活化参数敏感性研究

Sensitivity of geothermal fault activation parameters based on THMD multi-field coupling

地热能储层岩石具有低渗高温特点,但岩石中仍存在大量微裂隙、微孔洞等初始缺陷.岩体受到应力扰动或冷流体作用时会造成其力学性质发生变化进而导致初始缺陷进一步扩展演化形成岩石损伤.在损伤力学的基础上,本文根据岩石弹性模量Weibull概率随机分布构建了热-水-力-损伤模型.基于TOUGHREACT-FLAC3D框架,选取美国Coso地热田现场参数,建立含断层的三维数值模型,研究储层损伤演化与断层滑移的内在联系,并就地热开采的注入压力、注入温度和渗透率各向异性作敏感性分析.结果表明断层损伤导致断层的正应力退化是诱导断层活化失稳产生滑移的原因.不同流体注入压力和温度主要影响储层的应力状态与流体流动速度以改变损伤演化过程,进而改变断层滑移距离.储层渗透率变化将直接影响储层注入流体的压力损失.单向渗透率越大,储层整体损伤面积越小,断层受到持续热冲击的时间越长,断层滑移越大.

Geothermal energy reservoir have the characteristics of low permeability and high temperature,then a large number of initial defects such as micro-cracks and micro-cavitiesexisted in the inner of rock.Under the conditions of stress perturbation or thermal shock,the mechanical properties will be changed,which will lead to the further expansion and evolution of initial defects,and thus cause rock damage.On the basis of damage mechanics,this study proposed a thermal-hydraulic-mechanical-damage model based on the Weibull probability random distribution of rock elastic modulus.Based on the framework of TOUGHREACT-FLAC3 D,in-site parameters of the Coso geothermal field in the United States are selected and a three-dimensional numerical model containing faults is established to study the internal relationship between reservoir damage evolution and fault slip,and made the sensitivity analysis for injection pressure,injection temperature and permeability anisotropy.The results show that the normal stress degradation of the fault caused by the fault damage is one of the reasons for the slip caused by the instability of the fault activation.Different fluid injection pressure and temperature mainly affect the stress state of the reservoir and the fluid flow velocity to change the damage evolution process,and then change the fault slip distance.The variation of permeability determines the pressure loss of the fluid injected into the reservoir.The larger the unidirectional permeability,the smaller the overall damage area of the reservoir,the longer the fault will be subjected to continuous thermal shock,and the lager fault slip distance.