Research On The Longitudinal Vibration Characteristics Of The Drill String In Gas Drilling To Drill High-pressure Gas Reservoirs

Gas drilling technology is an important part of underbalanced drilling technology.Compared with liquid drilling,gas drilling technology drills faster and has better protection for reservoirs.Gas drilling will meet high-pressure gas layers while drilling high-pressure gas reservoirs,but after drilling high-pressure gas layers,it may lead to a series of complicated downhole accidents such as wellbore instability.Therefore,gas drilling encounters high-pressure gas layers,and identifying the conditions for drilling high-pressure gas layers becomes an important problem to be solved by gas drilling.In this paper,under the working condition of gas drilling drilling high pressure gas layer,the characteristics of vibration wave signal and acceleration signal generated by longitudinal vibration are studied,which provides a decision basis for quickly identifying the working conditions of drilling high pressure gas layer.The main research results of this paper are as followings:(1)Based on the propagation theory of stress waves in solids,established the longitudinal forced vibration model of the drill string,and derived the longitudinal wave equation of the gas drilling vibration wave.According to the longitudinal wave with faster propagation speed in the drill string,the longitudinal wave is used as the signal carrier,and the propagation characteristics of the longitudinal vibration wave in the drill string are studied.According to the constant structure,the wave impedance phenomenon occurs at the change of the cross-sectional area,analyzed the attenuation effect of different drill string sizes on the longitudinal wave signal.Studied the frequency response characteristics of periodic and aperiodic drill strings by transfer matrix method.Used the DX1 well drill string size to simulate the frequency response characteristics of the drill string.The results show that the drill string structure has comb-like filter properties,and the more complicated the drill string structure,the more complicated the filtering effect is.(2)Based on the longitudinal vibration theory of the drill string,established the longitudinal vibration model of the gas drilling drill string.Used the DX1 well parameters to analyze the vibration of the drill string before drilling the gas layer and after drilling the gas layer.Obtained Acceleration signal characteristics of the ground and drill string vibration characteristics of bottom hole,before drilling the open gas layer and after drilling the gas layer.(3)Analyzed the longitudinal acceleration random vibration signal collected in the DX1 well field by signal preprocessing analysis,signal time domain analysis and frequency domain analysis.The longitudinal acceleration signal is a regular sinusoidal or cosine periodic vibration signal,and there is a large correlation between the acceleration signals.Used the time period of the scene condition detected by the logging,the corresponding DX1 well acceleration signal is extracted for analysis,and the longitudinal acceleration signal characteristics of the movable drilling tool,the pure drilling and the drilling high pressure gas layer are analyzed.By comparing the characteristics of the acceleration signal on the scene with the characteristics of the acceleration signal obtained by simulation,obtained the vibration of the drill string.