射流式水力降压钻井机理与参数研究

Mechanism and parameter study of jet hydraulic drilling for decreasing bottomhole pressure

于水杰 李根生 罗洪斌 黄中伟

YU Shuijie LI Gensheng LUO Hongbin HUANG Zhongwei

中国石油大学油气资源与探测国家重点实验室，北京　102249 中国石化国际石油勘探开发公司，北京　100191

1. State Key Laboratory of Petroleum Resource and Prosp ecting, China university of Petroleum, Beij ing 102249, China 2 Sinop ec international Petroleum exp loration and Production Corp oration Beij ing 100191 China

窄密度窗口是钻井工程设计中的一个难点。为解决这一问题，提出了一种射流式水力降压原理，利用高速射流产生 的抽吸力降低井底压力（循环当量密度），并介绍了工具设计的基本思路。射流式水力降压工具由主副流道组成，副流道流体 在喷嘴处的高速低压区对环空产生抽吸作用。通过计算，降压效果随无量纲面积比、排量和喷嘴直径的增大而增大，随钻井速 度的增大而降低。在分流量5%、钻井液密度1.25 g/cm3 时，最大能降低井底压力1.5 MPa。该研究为射流式水力降压钻井应用 打下了基础。

Narrow window between fracture and pore pressure brings huge dificulty to drilling engineering. To solve the problem, a new jet hydraulic principle to decrease bottomhole pressure is proposed in this paper, i.e., using the suction power resulted from high speed jet to decrease bottomhole pressure (equivalent circulation density). And the basic idea of drilling tool design is introduced. The jet hydraulic bottomhole pressure decreasing tool includes main and secondary low path. Drilling luid lowing through the secondary path exerts sucking effect on annular at the high velocity and low pressure part of the nozzle. Calculation shows that the pressure decreasing effect gets better as the dimensionless nozzle-to-throat ratio, the low rate, and the nozzle diameter increase, but it gets worse as the drilling rate increases. The bottomhole pressure decreases by 1.5 MPa at the most in the condition that the low ratio between main andsecondary low path is 5% and the mud density is 1.25 g/cm3 .