水力射流降低井底压差技术

Reducing bottom-hole differential pressure by hydraulic jet

降低井底压差,减小岩屑的压持效应,可以显著提高钻井的机械钻速。根据射流式水力降压技术的原理,结合环空射流泵、射流降压短节和射流泵钻头等射流降压工具的发展现状,提出一种新型的环形射流泵结构,采用混合网格数值计算的方法对影响其降压性能的关键因素进行分析。结果表明:井底流体的回流是导致射流泵钻头降压效果变差的主要原因,回流量与井壁间隙成正比,与反向喷嘴的轴向倾角成反比;密封钻头与井壁间的间隙是提高射流泵钻头性能的关键;新型涡流-射流混合降压钻头可降压0.45～0.88 MPa,是现有射流式射流泵钻头降压效果的3～4倍。

Reducing the bottom-hole differential pressure （BHDP） and the cuttings hold-down effect can significantly improve the rate of penetration （ROP）. Based on the jet hydraulic pressure drawdown theory, the current research and development situation of the jet hydraulic pressure drawdown tools including annular jet pump, jet pump joint and jet pump bit, a peripheral nozzle jet pump bit was designed. Using hybrid grid method, the key factors affecting the depressurization capacity of the bit were analyzed. The results show that the main reason of reducing the depressurization capacity of the jet pump bit is the backflow of the bottom-hole fluid. The backflow rate is in direct proportion to the bit clearance and in inverse proportion to the angle between the reverse nozzle axis and the bit axis. To seal the bit clearance is the key point to improving the performance of the jet pump bit. The new vortex and jet pump combination bit can reduce the BHDP about 0. 45-0. 88 MPa, which is 3-4 times the depressurization effect of existing jet pump bit.