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<p>A large-scale hot dry rock (HDR) demonstration project was launched in 2019 in the Gonghe Basin, Qinghai Province, China. We present a comprehensive analysis of a 7-day injection test by integrating microseismic responses, fracturing parameters, logging curves, and field geological surveys. The temporal and spatial evolution characteristics of nearly 200 microseismic events were analyzed against the fluid injection strategy. Source mechanisms for several events of M<sub>W</sub> ~ 1.2 were retrieved to reveal the existence of complex natural discontinuities (e.g., natural fractures and structural planes) and their impacts on fracture propagation behavior. The high percentage of double-couple components (62.3% on average) suggested that the fractures mainly propagated along pre-existing fractures or geological discontinuities. Granite core samples and field investigations revealed extensively developed quartz veins at the HDR project site. Temporary plugging agents were utilized to enhance the fracture complexity in HDR reservoirs for the first time. The control of the maximum magnitude (M<sub>W</sub> ~ 2.0) of induced seismicity during the injectgion test and later large-scale fracturing stage suggested that temporary plugging agents have good potential for facilitating safe deep geothermal extraction. Besides, previous laboratory experiments with granite samples also revealed the abundant existence of quartz veins and their role in capturing hydralic fractures. A comprehensive study of multiple observations reveal the potential role of natural discontinuities (e.g., quartz veins) in affecting the creation and growth of hydraulic fractures, which will provide guidance for better exploiting deep HDR geothermal energy.</p>

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Role of Natural Discontinuities in Fracture Propagation in Hot Dry Rock: Observations and Implications from the Field Injection Test

  • 期刊论文

  • 发表日期：

    2025年1月4日

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  • Jingyu Xie,
  • Zhengguang Zhao,
  • Lei Li,
  • Hao Zhang,
  • Jing Zheng,
  • Wei Qiao,
  • Chongyuan Zhang,
  • Suping Peng,
  • Guiling Wang,
  • Dan Wang,
  • Xianpeng Jin

摘要

A large-scale hot dry rock (HDR) demonstration project was launched in 2019 in the Gonghe Basin, Qinghai Province, China. We present a comprehensive analysis of a 7-day injection test by integrating microseismic responses, fracturing parameters, logging curves, and field geological surveys. The temporal and spatial evolution characteristics of nearly 200 microseismic events were analyzed against the fluid injection strategy. Source mechanisms for several events of MW ~ 1.2 were retrieved to reveal the existence of complex natural discontinuities (e.g., natural fractures and structural planes) and their impacts on fracture propagation behavior. The high percentage of double-couple components (62.3% on average) suggested that the fractures mainly propagated along pre-existing fractures or geological discontinuities. Granite core samples and field investigations revealed extensively developed quartz veins at the HDR project site. Temporary plugging agents were utilized to enhance the fracture complexity in HDR reservoirs for the first time. The control of the maximum magnitude (MW ~ 2.0) of induced seismicity during the injectgion test and later large-scale fracturing stage suggested that temporary plugging agents have good potential for facilitating safe deep geothermal extraction. Besides, previous laboratory experiments with granite samples also revealed the abundant existence of quartz veins and their role in capturing hydralic fractures. A comprehensive study of multiple observations reveal the potential role of natural discontinuities (e.g., quartz veins) in affecting the creation and growth of hydraulic fractures, which will provide guidance for better exploiting deep HDR geothermal energy.