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 is 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 conclude 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.