水力喷射分段压裂密封机理

Sealing mechanism of the hydrajet stepwise fracturing

采用室内试验,结合计算流体力学方法,系统研究了水力喷射分段压裂过程中的密封机理,确定了影响射流密封性能的3个因素,即射流压力、喷嘴直径和套管孔眼直径,并获得了影响规律及计算模型。研究结果表明:高速射流周围存在低压区域,促使环空注入的高压液体流入喷射位置,然后在射流黏滞作用下被带入裂缝中,依靠射流实现密封;密封压力随射流压力和喷嘴直径增大而增加;套管孔眼能够防止孔道的高压液体影响密封压力,辅助高速射流,进一步增强其密封性能;水力喷射分段压裂技术应用于裸眼井时,射流密封性能有限。

The hydrajet fracturing（HJF） technique depends on a jet stream to achieve a sealing circumstance without any mechanical devices.The present paper systematically studied the sealing mechanism during the hydrajet stepwise fracturing by means of laboratory experiments combined with a computational hydramechanics method,and found three factors that influenced the sealing performance of a jet stream,namely jet-stream pressure,nozzle diameter and casing aperture diameter.Consequently,the paper proposed a law of the influence exerted by these factors and established a calculation model for the influence.The study results showed that there was a low-pressure region around the high-speed jet stream,resulting in the high-pressure fluid of annular water injection to flow to the very position,where it entered fractures under the viscous effect of the jet stream and formed a sealing circumstance.The sealing pressure increased with the increase of the jet-stream pressure and the nozzle diameter.In addition,the casing aperture could further assist the sealing performance of the high-speed jet stream by reducing the effect of the high-pressure fluid in the channel on the sealing pressure.However,the sealing performance of a jet stream was found to decline as the hydrajet stepwise fracturing technique was applied to an open-hole well.