水力喷射压裂孔道内部增压机制

Boosting mechanism in hydrajet-fracturing cavity

在室内试验基础上,结合计算流体力学方法,得到水力喷射压裂孔道内的压力分布,并对喷嘴压降、喷嘴直径、套管孔眼直径对孔道增压的影响进行分析。结果表明:在水力射流和套管孔眼密封的共同作用下,水力喷射产生的孔道内部存在增压现象,从而在套管压力低于地层起裂压力下压开地层;孔道压力随喷嘴压降和喷嘴直径的增大而增加;套管孔眼起到的密封作用能够大幅提高孔道压力,对孔道的增压影响很大;水力喷射压裂技术应用于裸眼井时,孔道增压有限,需要提高套管压力才能压裂地层。

Based on the in-house laboratory investigation,the pressure distribution in hydrajet-fracturing cavity was obtained by computational hydromechanics method. The effects of nozzle pressure drop,nozzle diameter and casing hole diameter on cavity pressure were analyzed. The results show that there is a boosting phenomenon within the jetted cavity resulting from the jetting stream and sealing of casing hole. Therefore,a fracture can be created when the pressure in the casing is less than the formation breakdown pressure. The pressure in cavity increases with the nozzle pressure drop and nozzle diameter increasing. The small hole in casing,which is the primary factor,plays sealing role to enhance the cavity pressure greatly. In an open hole well,the casing pressure should be increased to fracture formation due to the limitation of boosting within cavity.