Abstract
Geothermal energy is abundant and has a high economic development value. Perforation would need to be utilized to establish fluid channels between the borehole and geothermal reservoirs. In the present paper, it is proposed to use percussive drilling to create impact cracks near the borehole to improve abrasive water jet (AWJ) perforation performance. Two groups of the specimen were used for experiments. One was the specimen near the borehole after conventional rotary drilling (G1), the other was the specimen near the borehole after percussive drilling (G2). The optimal parameters of AWJ perforation assisted by percussive drilling were obtained. Through evaluation of AWJ perforation performance, it was found that the perforation depth, diameter and volume of G2 were 1.5 times, 1.3 times and 2 times of the G1, respectively. Besides, there were many internal cracks in G2, which interweave with each other and form a crack network. The results indicated that the impact cracks could change the mechanical properties of the granite near the borehole, then reduce the difficulty of AWJ perforation and improve the perforation performance. All the above merits can provide important technical support for reducing the fracturing pressure, increasing fluid flow and enhancing heat exchange efficiency between geothermal reservoir and borehole.
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