| Title | Research of High-temperature Diverting Fracturing Technology for EGS Projects |
|---|---|
| Authors | CHEN Peipei, CHEN Wenyi, ZHANG Liru, LI Jingang, GAO Yang, WANG Zhihai |
| Year | 2022 |
| Conference | Stanford Geothermal Workshop |
| Keywords | segmented fracturing, diverting fracturing, EGS, temporary plugging agent |
| Abstract | Increasing the flow rate of heat-transfer medium and the contact area with formation are the important methods to improve the heat transfer efficiency of enhanced geothermal system (EGS). Bullhead fracturing is commonly used in EGS projects, yet it is difficult to create multiple fractures in formation, thus resulting in the lower flow rate of heat-transfer medium and inefficient heat transfer. Segmented fracturing technology provides finer control over the number of fractures, which could boost energy production capacity. However, traditional segmented fracturing relies on mechanical packers or low temperature diverters, unadaptable to high temperature ( greater than 150℃) environment of EGS. Therefore, research on high-temperature diverting fracturing technology for deep EGS is significant in both theory and applications. The core of high-temperature diverting fracturing is developing high-temperature diverters. In this study, a newly developed hydrofracture diverter has shown multiple advantages over conventional diverters. It features low density(1.10 g/cm3-1.20 g/cm3), excellent high temperature (250℃) and high pressure(180Mpa) resistant properties as well as degradability. Its self-degradation rate is less than 5% for 24h and greater than 30% for 96h in 250℃ water environment. Furthermore, high-temperature diverting fracturing simulation experiments were designed and performed with the ultra-high-temperature true tri-axial equipment. The test results showed that the diverter could not only plug fractures for 48 hours in 250°C environment, but was also capable of sealing cracks under 38MPa and turned to create new fractures. The flow-back rate exceeded 90% after self-degradation for 120h, which further verified the effectiveness of the technology. High-temperature diverting fracturing offers a more efficient approach to extract geothermal energy. The proprietary diverter can be employed in 250℃ formations and adjustment of composition can lead to different high temperature resistant properties. Next, field tests will be conducted to assess the effectiveness and application conditions for the technology. |