A damage mechanics approach to the simulation of hydraulic fracturing/shearing around a geothermal injection well
A damage mechanics approach to the simulation of hydraulic fracturing/shearing around a geothermal injection well
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DOI：
10.1016/j.compgeo.2015.10.003
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发表时间：
2016
影响因子：
5.3
通讯作者：
J. Pogacnik;D. Elsworth;M. O'Sullivan;J. O'Sullivan
中科院分区：
文献类型：
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作者：
J. Pogacnik;D. Elsworth;M. O'Sullivan;J. O'Sullivan
提高地热能产量需要刺激天然裂缝通道，以增加储层内的流体流量，同时仍然有效地回收热量。在注入/生产过程中，储层渗透率随着时间的推移表现出不同程度的增强或下降。这些变化通常归因于短期刺激和长期生产过程中发挥作用的各种多物理过程。重要的增产机制包括水力压裂引起的拉伸破坏或水力剪切引起的剪切破坏。已使用多种方法对多孔和裂缝介质中的渗透率增强进行数值模拟，包括基于损伤力学、离散断裂力学、临界剪切应变准则、有效应力甚至经验渗透率乘数的模型。我们探索使用损伤力学来表示储层内的水力压裂/剪切。该模型采用混合模式（张开 – I 和剪切 – II）的能量释放率微裂纹模型来模拟损伤和渗透性增强。该模型根据压缩测试进行校准，以确定损伤与变形和渗透率之间的相互关系。然后将其用于对比用冷流体注入刺激热储层期间的等温和热淬灭效应。结果表明，当流体压力处于亚破坏状态时，破坏区域仅限于近井筒区域。随着流体压力的增加，近井筒II型故障转变为I型水力压裂，损害迅速增加。地热行业需要一种模拟因剪切和拉伸破坏而引起的冷水注入损伤的方法。这项工作朝这个方向迈出了一步。
Enhanced geothermal energy production requires the stimulation of natural fracture pathways to increase fluid flow within a reservoir while still effectively recovering the heat. During injection/production, reservoir permeability exhibits various degrees of enhancement or degradation with time. These changes are generally attributed to various multiphysics processes that act both during short-term stimulation and during production over the longer term. Important mechanisms of stimulation include tensile failure by hydraulic fracturing or shear failure by hydraulic shearing. A wide range of methods have been used to numerically simulate permeability enhancement in porous and fractured media including models based on damage mechanics, discrete fracture mechanics, critical shear strain criteria, effective stress, and even empirical permeability multipliers. We explore the use of damage mechanics to represent hydraulic fracturing/shearing within the reservoir. The model incorporates an energy release rate microcrack model in mixed modes (opening – I and shear – II) to simulate damage and permeability enhancement. The model is calibrated against compression tests to determine interrelationships between damage and both deformation and permeability. It is then applied to contrast both isothermal and thermal quenching effects during stimulation of hot reservoirs with cold fluid injection. The results illustrate that when fluid pressures are sub-failure, the damage zone is limited to the near wellbore region. As fluid pressure is increased, near wellbore mode II failure transitions to mode I hydraulic fracturing and rapidly increasing damage. A method of simulating cold water injection induced damage due to both shear and tensile failures is needed in the geothermal industry. This work offers a step forward in that direction.