Numerical Simulation of Hydraulic Fracturing in Enhanced Geothermal Systems Considering Thermal Stress Cracks
Numerical Simulation of Hydraulic Fracturing in Enhanced Geothermal Systems Considering Thermal Stress Cracks
复制标题
DOI：
10.1007/s00024-022-02996-z
复制
发表时间：
2021-06
影响因子：
2
通讯作者：
Ziyang Zhou;H. Mikada;J. Takekawa;Shibo Xu
中科院分区：
文献类型：
--
作者：
Ziyang Zhou;H. Mikada;J. Takekawa;Shibo Xu
近年来，随着人们对清洁和经济能源的日益关注，地热能和增强型地热系统（EGS）越来越受到重视。为了有效开发深部地热储层，了解高温高围压环境下储层岩石的力学行为及其与注入流体的相互作用，是采用水力增产技术的关键。在本研究中，我们开发了一种新的数值格式的基础上的离散元法（DEM）来模拟岩石的破坏行为，考虑到热应力裂纹和高围压的影响EGS。通过不同温度下的单轴压缩试验和不同围压下的双轴压缩试验与室内试验结果的比较，验证了所提出的方法的有效性。数值计算结果表明，破坏模式和应力-应变曲线与室内试验结果吻合较好。然后，我们将开发的计划在各种温度，围压和注入流体条件下的水力压裂模拟。根据我们的数值计算结果，水力裂缝的数量与温度成正比。在高温低围压条件下，可以观察到复杂的裂纹网络，裂纹宽度较大，而在高围压条件下，微裂纹的产生受到抑制。此外，高粘度的注入流体更容易诱发水力裂缝。由于地热储层中的裂缝网络是地热能有效生产的重要因素，因此在EGS的水力压裂处理中应考虑上述因素的组合。
With the increasing attention to clean and economical energy resources, geothermal energy and enhanced geothermal systems (EGS) have gained much importance in recent years. For the efficient development of deep geothermal reservoirs, it is crucial to understand the mechanical behavior of reservoir rock and its interaction with injected fluid under high-temperature and high confining pressure environments for employing hydraulic stimulation technologies. In the present study, we develop a novel numerical scheme based on the distinct element method (DEM) to simulate the failure behavior of rock by considering the influence of thermal stress cracks and high confining pressure for EGS. The proposed methodology is validated by comparing uniaxial compression tests at various temperatures and biaxial compression tests at different confining pressures with laboratory experimental results. The numerical results indicate a good agreement in terms of failure models and stress-strain curves with those of laboratory experiments. We then apply the developed scheme to the hydraulic fracturing simulations under various temperatures, confining pressures, and injection fluid conditions. Based on our numerical results, the number of hydraulic cracks is proportional to the temperature. At a high-temperature and low confining pressure environment, a complex crack network with large crack width can be observed, whereas the generation of the micro-cracks is suppressed in high confining pressure conditions. In addition, high-viscosity injection fluid tends to induce more hydraulic cracks. Since the crack network in the geothermal reservoir is an essential factor for the efficient production of geothermal energy, the combination of the above factors should be considered in hydraulic fracturing treatment in EGS.