Abstract We present key observations and analyses of the first and second stimulations conducted at the Pohang enhanced geothermal system (EGS) site in Korea in 2016. The first hydraulic stimulation was conducted in the PX-2 well of 4.3 km depth, with the maximum wellhead pressure of 89.2 MPa, the maximum injection rate of 46.8 L/s, and a total injected volume of 1970 m3. The first stimulation showed non-linear and reversible fracture-opening behavior with injection pressure increase. The stimulation mechanism of PX-2 is interpreted as a combination of tensile fracture extension and hydraulic jacking. The second hydraulic stimulation was conducted in the PX-1 well of 4.2 km depth, with the maximum wellhead pressure of 27.7 MPa, the maximum injection rate of 18.0 L/s, and a total injected volume of 3907 m3. The fracture-opening pressure of PX-1 was evaluated from the clear pressure peaks and the pressure at differential injectivity increase, and was drastically lower than that of PX-2. The transmissivity of PX-1 permanently increased by 6.4 times during the second stimulation. The wellhead injectivity of PX-1 was 3.6 times as high as that of PX-2 at the same injection rate. The stimulation mechanism in PX-1 is interpreted as a combination of hydraulic shearing and hydraulic jacking of unmated or shear-dilated fracture. Both stimulations in the two wells showed consistently greater seismicity rate and magnitude during the shut-in phases than during the preceding injection phases. A close correlation between the injected fluid volume and seismic magnitude was observed in both wells, and the seismic events induced by the two stimulations were in general below the maximum magnitude envelopes expected by the previous studies. Despite the close distance of approximately 600 m in the same rock formation, the two wells showed distinctly different behavior in terms of the overall pressure ranges, pressure peaks, pressure for injectivity increases, transmissivity changes, and the stimulation mechanisms due possibly to the heavy mud and lost circulation material used during the drilling and completion of PX-2. The contrasting hydromechanical responses observed in the same reservoir at the two nearby wells emphasize the importance of proper drilling and completion with close consideration of stimulation strategy.

中文翻译：

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韩国浦项地热开发区前两次水力增产的观测与分析

摘要 我们介绍了 2016 年在韩国浦项增强型地热系统 (EGS) 站点进行的第一次和第二次增产的主要观察和分析。第一次水力增产在 4.3 公里深度的 PX-2 井中进行，最大井口压力89.2 MPa，最大注入速度46.8 L/s，总注入量1970 m3。第一次增产随着注入压力的增加显示出非线性和可逆的裂缝打开行为。PX-2 的增产机制被解释为拉伸裂缝扩展和液压顶升的组合。第二次水力改造在PX-1井进行，井深4.2 km，最大井口压力27.7 MPa，最大注入量18.0 L/s，总注入量3907 m3。PX-1的开裂压力从压力峰清晰和差注压力增大来评价，明显低于PX-2。在第二次刺激期间，PX-1 的透射率永久增加了 6.4 倍。在相同注入速度下，PX-1 的井口注入能力是 PX-2 的 3.6 倍。PX-1 中的增产机制被解释为未配合或剪切扩张裂缝的液压剪切和液压顶升的组合。与之前的注入阶段相比，在关井阶段，两口井的两种增产措施都显示出持续更高的地震活动率和震级。在两口井中都观察到注入流体量与地震震级之间的密切相关性，并且这两种刺激引起的地震事件总体上低于先前研究预期的最大震级包络。尽管在同一岩层中相距约 600 m，但两口井在总体压力范围、压力峰值、注入压力增加、导水率变化以及可能由于重泥浆引起的增产机制方面表现出明显不同的行为PX-2 钻井和完井过程中使用的堵漏材料。在附近两口井的同一油藏中观察到的对比流体力学响应强调了正确钻井和完井并密切考虑增产策略的重要性。尽管在同一岩层中相距约 600 m，但两口井在总体压力范围、压力峰值、注入压力增加、导水率变化以及可能由于重泥浆引起的增产机制方面表现出明显不同的行为PX-2 钻井和完井过程中使用的堵漏材料。在附近两口井的同一油藏中观察到的对比流体力学响应强调了正确钻井和完井并密切考虑增产策略的重要性。尽管在同一岩层中相距约 600 m，但两口井在总体压力范围、压力峰值、注入压力增加、导水率变化以及可能由于重泥浆引起的增产机制方面表现出明显不同的行为PX-2 钻井和完井过程中使用的堵漏材料。在附近两口井的同一油藏中观察到的对比流体力学响应强调了正确钻井和完井并密切考虑增产策略的重要性。以及 PX-2 钻井和完井过程中使用的重泥浆和堵漏材料可能导致的增产机制。在附近两口井的同一油藏中观察到的对比流体力学响应强调了正确钻井和完井并密切考虑增产策略的重要性。以及 PX-2 钻井和完井过程中使用的重泥浆和堵漏材料可能导致的增产机制。在附近两口井的同一油藏中观察到的对比流体力学响应强调了正确钻井和完井并密切考虑增产策略的重要性。