Experimental Study On Downhole Pressure Fluctuation In Complex Drilling Condition Of MPD

As exploring and drilling in the high temperature formation,narrow mud density window formation and other challenging formations,drilling is faced with severe challenges.The Managed pressure drilling technology is an important way to deal with complex drilling conditions and improve drilling safety by means of annulus pressure control.Conventional Managed pressure drilling mainly depends on the pressure signal measured near the drill bit,but it is difficult to accurately reflect the change of downhole conditions.If a point is added at a certain distance above the drill bit,then we can compare the difference between the two measuring points at the same time.So the real-time identification is done underground with the results directly to the ground.In this paper,the experimental study on the bottom hole pressure change is carried out during the process of gas invasion and leakage and the signal change characteristics are studied.In this paper,an experimental device for gas invasion and leakage is established,including the simulation of wellbore and related equipment,signal acquisition system,etc.The similarity analysis is also carried out.Simultaneous measurement of pressure signals can be achieved.The pressure signal analysis method is established based on the theory of digital signal analysis.Signal analysis program is written for the experimental data.The change of downhole pressure signal can be caused by gas invasion and leakage.This paper studies the pressure signal amplitude and frequency variation in the occurrence of gas invasion and leakage.When the gas invasion occurs,the pressure signal amplitude increases and the signal fluctuation is obvious.When leakage occurs,the value of the pressure signal is shifted to the left and the amplitude decreases.In the spectrum of the pressure signal,a lot of complex low frequency signals are produced when the gas invasion and leakage occur.The time of change can be located by the detailed signal after multilevel wavelet decomposition.The analysis of signal characteristics can not rely on only one method.The results are helpful for the early identification of gas invasion and leakage conditions...