井下微流量控制方法

A method of bottom-hole micro-flux control

近几年,国外在常规钻井和欠平衡钻井技术的基础上发展出了一种被称为控压钻井(MPD)的新技术,该技术主要用于解决窄钻井液密度窗口地层的安全钻井问题,其核心是要求精确控制井眼环空压力剖面。但作为一种新的钻井技术,控压钻井现有的方法理论和硬件系统尚存在一定的不足,有待于完善。文中介绍的井下微流量控制方法属于控压钻井技术中的一种,是对现有地面微流量控制方法的改进,能够随钻监测井下环空流量的变化,及早发现溢流或井漏等井下复杂情况,与地面返出环空流量监测相配合,进而调节井口回压阀的开度,通过改变井底压力来控制溢流或井漏的大小,从而实现对环空流量的精确控制。该方法能够显著提高系统的控制精度和可靠性,从而提高钻井的安全性并降低钻井成本。

In the past few years,a new technique called managed pressure drilling(MPD) has been developed abroad on the basis of conventional drilling and underbalanced drilling.MPD is mainly used for safe drilling through formations with narrow drilling fluid window and its core point is to precisely control the annulus pressure profile.But as a brand new technique,MPD still has some shortcomings in theory and hardware system to be overcome.The downhole micro-flux control method mentioned here in this paper is a new kind of MPD,which is an improvement of the existing surface micro-flux control methods.By use of this new method,we can detect the downhole annulus flow rate variation while drilling so as to observe the overflow and lost circulation as early as possible.In combination with the annulus flow rate monitoring at the surface and the wellhead back-pressure valve opening adjustment,the bottomhole pressure can be changed accordingly to control the size of overflow and lost circulation,the drilling safety can thus be improved and the drilling cost can be reduced.