Study On The Fluctuation Pressure Of The Wellbore Caused By The Drilling Process

Well control technology plays an important role in oil-gas field exploration and development. However, control of fluctuating pressure is an important guarantee to realize safe, economical and high-efficiency well control in well drilling operation. Without appropriate treatment on the speed of wellbore tripping operation, fluctuating pressure may occur, which may lead to borehole collapse in tripping down operation and blowout in tripping out operation. To avoid these complex conditions, fluctuating pressure caused by wellbore tripping operation should be strictly controlled. Thus, the effect of fluctuation pressure in wellbore tripping operation should be taken into consideration in drilling design and construct. So far, the calculation of wellbore fluctuating pressure is the issue worth further research.In the actual operation condition, the solving methods for wellbore fluctuating pressure calculating model are proposed by combining with the initial condition and boundary condition of open tube, plugging tube, pumping on and off operation. According to the fluctuating pressure calculating model, the software for gas-liquid two phases fluctuating pressure calculating in wellbore is designed by using Visual Basic.NET language. The influence factors of fluctuating pressure are analyzed quantitatively to reveal the relationship between fluctuating pressure and drilling parameters. The calculating formula and charts are presented for field production application.The results show that the designed fluctuating pressure calculating software can not only predict the maximum fluctuating pressure but also predict the maximum allowable tripping speed. Analysis of influence factors shows that the fluctuating pressure at the bottom of the well will increase, the allowable maximum tripping speed will decrease and the safe drilling fluid density window will be narrowed, if one of the condition appears, such as the fraction of gas is decreased, or outer diameter of the drilling stem is increased, or the outer diameter of drilling collar is increased, or the depth of the well is increased, or the density of drilling fluid is boosted, or the length of drilling collar is enlarged. The research on the fluctuating pressure of gas-liquid two phases in wellbore tripping operation can provide theoretical foundation for designing of drilling parameters and predicting of fluctuating pressure in tripping operation.