Potential of fixed-plane-perforation fracturing technique in enhanced geothermal system

Fixed-plane-perforation fracturing (PFFP) has been employed to construct complex fracture networks to stimulate unconventional reservoirs. Few studies have been reported on its application potential in geothermal energy extraction. Here we first introduced the PFFP to the enhanced geothermal system (EGS) and numerically examined its heat extraction performance by comparing to those of differing stimulation strategies. We found that much longer fractures and significantly larger damage area are induced by the PFFP than the single -perforation fracturing (SPF), and the heat extraction of the reservoir stimulated by the FPPF is approximately 60% higher than that by the SPF, suggesting the great potential of the PFFP in deep geothermal energy harvest. We further improved our previously-proposed sensitivity indicator to assess the influence degree of critical factors on the PFFP where fracture networks were characterized by the pore pressure of hot dry rock. We found that a high in-situ stress difference reduces the spacing between hydraulic fractures and increases the stress shadowing, causing an increase in heat extraction. The injection rate affects strongest on fracture network area whereas the initial fracture angle is the least. When the injection rate increases from 0.0005 m3/s to 0.0020 m3/s, the internal fracture length grows by 61.3%, the fracture network area expands by 74.7% of the total area, and the heat extraction increases by 54 GJ. Our findings benefit hydraulic stimulation strategy selection and heat extraction optimization over EGS construction.

Automated summary

Fixed-plane-perforation fracturing (PFFP) has been introduced to enhance geothermal system (EGS) and has shown potential to stimulate longer fractures and achieve higher heat extraction compared to single-perforation fracturing (SPF). By using an improved sensitivity indicator, the injection rate is found to significantly affect the fracture network area, while the in-situ stress difference has the greatest impact on heat extraction.