Injection Induced Seismicity in Hot Resevoirs

增强型地热系统可能是美国清洁、可持续能源供应的主要贡献者。 增强型地热储层是一种工程地下热交换器，旨在改善传统的热液储层，或在热储层岩石具有低渗透性的情况下创建循环系统。 这通常通过注入加压流体来完成。 这种注入已被证明会诱发地震活动。了解为什么会发生注入诱发的地震活动是利用这一资源的基础。 了解诱发地震活动的机制对于开发该国丰富的页岩气储量和碳封存也是必要的。 由于注水诱发地震的机制十分复杂，目前对注水诱发地震的机制还缺乏深入的认识。 该项目将在非常专业的设备上进行一系列实验，这些设备可以模拟间歇泉地热田。 这将使工程师对诱发地震活动背后的机制有所了解，以便可以在不引起地震的情况下使用地下注入的能源资源。该项目基于精心设计的测试序列，每一个都为下一个提供信息。 第一阶段是研究断层卸荷与增加剪切载荷对前震和破裂的影响。 格拉泽的初步工作表明，动力学是完全不同的。 这些实验将在实验室的地震机器中进行。 下一组实验将在格拉泽实验室的真三轴地热储层模拟器中进行。该设备的组成部分是一个高压锅炉，用2 MPa的蒸汽淹没250 mm的岩石立方体，复制间歇泉油田。试样将被破碎，以代表岩体，而不是一个固体立方体的岩石。 我们将研究热收缩的影响，以及注入水闪蒸成蒸汽，作为断层弱化的近因。 将对贯穿和增长的水力裂缝进行建模。 将通过纳米地震成像研究导致宏观破裂的动态凹凸水平位移“种子”。 这是通过绝对校准的纳米地震传感器实现的，其噪声基底为0.2 pm。 多年来，实验室分析方法已经开发的基础上使用的地震学家的工具，以准确地测量破裂运动学的绝对指标，包括源时间函数的mN灵敏度。 由于类似的工具被用来研究间歇泉的地震活动性，因此可以合理地缩放我们的结果。

Enhanced geothermal systems are potentially a major contributor to the nation's supply of clean, sustainable energy. An enhanced geothermal reservoir is an engineered subsurface heat exchanger designed to improve a conventional hydrothermal reservoir, or to create a circulation system where hot reservoir rocks have low permeability. This is most often done by injection of pressurized fluids. This injection has been shown to induce seismicity. Understanding why injection-induced seismicity occurs is fundamental for utilizing this resource. Understanding the mechanisms of induced seismicity is also necessary for the exploitation of the country's rich deposits of shale gas, and for carbon sequestration. Because the in situ mechanisms of injection induced seismicity are so complex, there still is a lack of deep understanding. The project will carry out a set of experiments in very specialized equipment that can model the Geysers geothermal field. This will bring the understanding needed to engineer for the mechanisms behind induced seismicity so that subsurface injection of fluids for energy resources can be used without causing earthquakesThe project is based on a carefully designed sequence of tests, each informing the next. The first stage is the investigation of the effects of fault unloading vs. increased shear loading on foreshocks and rupture. Preliminary work by Glaser shows that the dynamics are quite different. These experiments will take place in a laboratory earthquake machine. The next set of experiments will take place in the Glaser lab's true-triaxial geothermal reservoir simulator. Integral to this device is a high pressure boiler that floods 250 mm cubes of rock with 2 MPa steam, duplicating the Geysers field. Specimens will be fractured to represent a rock mass rather than a solid cube of rock. We will investigate the effects of thermal contraction, and injected water flashing to steam, as proximate causes of fault weakening. Both through-going and growing hydraulic fractures will be modeled. The dynamic asperity-level displacement "seeds" that lead to macro-rupture will be studied through nano-seismic imaging. This is made possible by absolutely-calibrated nanoseismic sensors, which have a noise floor of 0.2 pm. Over many years, laboratory analysis methodologies have been developed based on tools used by seismologists, to accurately measure absolute metrics of rupture kinematics, including the source-time function to mN sensitivity. Because similar tools are used to study seismicity at the Geysers, it is possible to reasonably scale our results.