全球干热岩资源开发诱发地震活动和灾害风险管控

Review of induced seismicity and disaster risk control in dry hot rock resource development worldwide

干热岩地热资源作为一种绿色可再生的新型能源,其开发利用已成为当前世界各国尤其是发达国家能源战略的重要组成部分.但由于干热岩位于地壳浅部3~10 km,在采用增强型地热系统(EGS)等通用开发方式过程中,伴随着地壳应力状态的扰动,部分开采项目发生较大震级的诱发地震事件,甚至造成明显灾害、引起社会问题,亟待实现科学利用和风险管控.鉴于此问题在平衡能源开发战略和社会安全领域的重要性和关键性,本文梳理了全球干热岩开采诱发地震的总体情况、典型案例,整理了在成因和机理研究、地震灾害风险管控和缓解等方面的研究进展.综合分析结果表明,已有EGS项目案例中诱发地震震级超过3.0的达到31.2%、主要与断层活化有关,最大的诱发地震可发生在注水压裂、关井后、循环生产等各阶段.干热岩开采诱发地震有多种成因,已有案例多为多种成因共同作用,其中的关井后的尾随效应是目前重大难点.目前世界各国已开展了广泛的诱发地震机理研究并探索多种减灾措施,认为累积注水体积、注水速率与最大诱发震级之间不存在普适性的定标关系,前瞻性预测需要采用“一井一策”的方式.在缓解诱发地震灾害风险上,普遍采用科学的流体注入策略、对注采策略进行验证校准、持续开展地震活动监测等系列措施.此外,对储层的临界应力状态和应力时空演化的量化描述、地热储层内的先存断层与裂缝的探测识别、可有效管控地震发生的流体注入策略等,是当前干热岩资源开发减轻地震风险的主要技术难点,而利用地热储层实时感知信息技术、采用新的注入热交换载体、发展前瞻性的地震预测方法是该领域目前重点关注的技术方向.根据我国的干热岩资源开发和减轻地震灾害风险的实际情况,亟待建立开采场地安全性和灾害风险评价、多学科的地震监测网络和分析技术、地震灾害风险管控红绿灯系统等技术体系,并加强关井后的尾随现象、多场耦合等科学问题的基础研究.

The hot dry rock geothermal resource is a new type of green and renewable energy.Its exploitation and utilization have become an important part of energy strategy in the world,especially in developed countries.However,as the hot dry rock is located at 3~10 km depth in the shallow crust,in the process of enhanced geothermal system(EGS),along with the disturbance of crustal stress state,some exploitation projects have induced sizable earthquakes,even causing significant disasters and social problems.In view of the importance of this problem in balancing energy exploitation strategy and social security,we summarize the global general situation and typical cases of induced earthquakes by hot dry rock exploitation,and sorts out the research progress in aspects of causes and mechanisms,earthquake disaster risk management and control technology.The comprehensive analysis results show that induced earthquakes with a maximum magnitude over 3.0 among current EGS project cases reach 31.2%,which are mainly related to fault activation.The largest induced earthquake can occur in various stages such as hydrofracking,injection well shut-in,and cyclic production.There are multiple causes for the induced earthquakes,and most of the current cases are interactions of multiple causes,among which the tailing effect after well shut-in is a major difficulty.At present,a variety of disaster reduction measures have been explored all over the world.There is no universal calibration relationship between the cumulative water injection volume,water injection rate,and the maximum magnitude of induced earthquakes.The forward prediction needs to adopt the measure of“one well,one strategy”.In order to mitigate the risk of disaster by induced earthquakes,a series of measures are generally adopted,such as scientific fluid injection strategy,verification and calibration of injection production strategy,and continuous seismic activity monitoring.In addition,the quantitative description of critical stress state and spatiotemporal evolution of stress,detection and identification of pre-existing faults and fractures in the geothermal reservoir,and fluid injection strategy that can effectively control the occurrence of earthquakes are the main technical difficulties in the development of dry hot rock resources to reduce seismic risk.However,using real-time sensing information technology of geothermal reservoir,adopting new injection heat exchange carrier,and developing prospect are also discussed.At present,the key technology direction in this field is to improve the accuracy of earthquake prediction.According to the actual situation of dry hot rock resources development and earthquake disaster risk reduction in China,it is urgent to establish the technical system of mining site safety and disaster risk assessment,multi-disciplinary seismic monitoring network and analysis technology,earthquake disaster risk management,and control traffic light system,and strengthen the basic research of scientific problems such as tailing phenomenon after shut-in and multi-field coupling.