不灌浆条件下的最大安全起钻高度计算

起钻是钻井中必然出现的作业工况,起钻过程中随着钻具的起出会导致井筒中环空液面下降。基于井控安全考虑,必须及时灌浆增加井筒中静液柱压力平衡井底地层压力。针对不灌浆情况下的最大安全起钻高度,目前通常是遵照经验作法和管理规范执行,科学定量计算较少,因此进行了计算方法研究。本文在保证井底压力不变的基础上,先根据井底垂深、井底地层压力系数及井内钻井液密度计算环空液面最大允许的下降高度;根据井身结构和钻具参数,分"干起"和"湿起"两种工况,总结了不灌浆情况下的最大安全起钻高度计算方法,并以X井为例说明了该方法的应用。研究结果得出,其他条件相同的情况下,"湿起"比"干起"的最大安全起钻高度短,井控风险更大,需要较频繁地灌浆;随着钻杆钢级的增加,最大安全起钻高度减小,但是变化不大。本文提出的不灌浆起钻的最大安全起钻高度科学计算方法,可为安全起钻作业提供指导。

Calculation of the maximum safe tripping out height under the condition of no fill up

Tripping is an inevitable operation mode of drilling, and the top of drilling fluid in the annular will drawdown during that process. Based on well control safety, filled up operation must be timely carried out to increase hydrostatic column pressure to balance the formation pressure at bottom hole. For the maximum safety tripping out height without filling up, the experience practice and management regulation are usually followed, and scientific quantitative calculation was rarely reported but is really needed. In this paper, the maximum permissible height reduction of annulus drilling fluid level is calculated, according to the vertical depth, drilling fluid density and formation pressure coefficient at the bottom hole, on the basis that bottom hole pressure is constant; Calculation method for the maximum safety tripping out height without filling up operation are summarized, aiming at "dry" and "wet" two kinds of working conditions and according to the casing program and drill string, and then take well X as an example to illustrate how to use this method. The results of the study concluded that, the maximum safety tripping out height of "wet" condition is shorter than that of "dry" working condition under same situations,so well control risk is more serious and more frequent fill up is needed; With the increase of drill pipe steel grade, the biggest security drill height decrease, but the range is not big. The proposed the maximum safety height calculation method without filling up can provide guidance for safety tripping out operations.