First field application of cyclic soft stimulation at the Pohang Enhanced Geothermal System site in Korea
First field application of cyclic soft stimulation at the Pohang Enhanced Geothermal System site in Korea
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DOI：
10.1093/gji/ggz058
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发表时间：
2019-05-01
影响因子：
2.8
通讯作者：
Kim, Kwang Yeom
中科院分区：
文献类型：
--
作者：
Hofmann, Hannes;Zimmermann, Guenter;Kim, Kwang Yeom
大规模流体注入诱发的地震事件是全球地热能开发的潜在风险。一个潜在的风险缓解措施是应用循环注入计划。在小验证后从2017年8月7日到8月14日，该概念首次在韩国浦项增强型地质勘探系统（EGS）现场应用于现场规模。从2017年8月7日到8月14日，总计1756 m（3）的地表水以1到10 l s（-1）的流速注入浦项PX-1井，最大井口压力（WHP）为22.8 MPa，根据现场特定的循环软刺激计划和交通灯系统。在注入期间和注入后不久，共检测到52次诱发微震，最大的M-W 1.9。在那次事件之后，大约1个月内从井中总共生产了1771 m3的水，在此期间没有观察到更大规模的地震事件。水力数据集显示，随着裂缝开口在15和17 MPa WHP之间，注入能力随压力而增加，但没有观察到显著的永久性transmittance增加。在刺激期间，诱发地震活动的最大幅度低于M-w 2.0的目标阈值，并获得了有关刺激储层的额外知识。此外，评价了油田规模周期注水的技术可行性。限制最大地震震级的主要因素被认为是：限制注入的净流体体积，最大诱发地震事件发生后的回流，使用循环注入方案，交通灯系统的应用，以及在处理设计中包括来自先前调查和操作的先验信息。
Large-magnitude fluid-injection induced seismic events are a potential risk for geothermal energy developments worldwide. One potential risk mitigation measure is the application of cyclic injection schemes. After validation at small (laboratory) and meso (mine) scale, the concept has now been applied for the first time at field scale at the Pohang Enhanced Geothermal System (EGS) site in Korea.From 7 August until 14 August 2017 a total of 1756 m(3) of surface water was injected into Pohang well PX-1 at flow rates between 1 and 10 l s(-1), with a maximum wellhead pressure (WHP) of 22.8 MPa, according to a site-specific cyclic soft stimulation schedule and traffic light system. A total of 52 induced microearthquakes were detected in real-time during and shortly after the injection, the largest of M-w 1.9. After that event a total of 1771 m(3) of water was produced back from the well over roughly 1 month, during which time no larger-magnitude seismic event was observed. The hydraulic data set exhibits pressure-dependent injectivity increase with fracture opening between 15 and 17 MPa WHP, but no significant permanent transmissivity increase was observed.The maximum magnitude of the induced seismicity during the stimulation period was below the target threshold of M-w 2.0 and additional knowledge about the stimulated reservoir was gained. Additionally, the technical feasibility of cyclic injection at field scale was evaluated. The major factors that limited the maximum earthquake magnitude are believed to be: limiting the injected net fluid volume, flowback after the occurrence of the largest induced seismic event, using a cyclic injection scheme, the application of a traffic light system, and including a priori information from previous investigations and operations in the treatment design.