Numerical Simulation Of Flow In Well For Overflow And Leakage Accident Induced By Drill String Dropped

With the continuous exploration of complex formations in the field of oil and gas exploration and development,the probability of drilling accidents increases and becomes more complex.It increases the difficulty of well control and disposal,and it is a difficulty that must be overcome to study the flow state in the well under the overflow accident.In this thesis,the method of numerical simulation is used to study the flow state of the overflow and leakage well,and the corresponding calculation module is developed based on the selected model.Firstly,a leakage model based on one-dimensional radial fracture drilling fluid flow was selected,and the effects of different drill string drops and fracture widths on leakage were analyzed;Then,based on the characteristics of gas invasion,the overflow model was selected and solved discretely to analyze the change rules of key parameters in the process of leakage induced overflow,and to comprehensively analyze the complex well conditions.This thesis draws the following conclusions: different types of drilling tools produce different surge pressures,resulting in different risk levels;the leakage caused by the surge pressure changes the fastest in the first 60 s of the leakage;the effect of the fracture width on the leakage rate is more sensitive than that of the surge pressure;the overflow caused by the leakage caused by the drop of the drill string is different from that of the conventional overflow accident.The change of the gas holdup with the depth of the well can be regarded as a three-stage distribution;the lower the initial liquid level,the more obvious the expansion of the invaded gas at the bottom of the hole;between2000 and 2500 s,gas is ejected from the wellhead at a small flow rate.If no measures are taken at the wellhead,the gas at the wellhead will be ejected with time the flow will increase rapidly,resulting in uncontrollable on-site blowout,and the well should be shut in as soon as possible.Finally,this thesis analyzes the overflow and leakage accident caused by the drop of the drill string in a well.The simulation results are close to the time from the drop of the drill string on site to the return of the wellhead.Using the calculation module developed in this thesis,we can understand the unknown situation in the accident wells,invert the accident and sum up the experience of the accident well,and also can simulate and preview the possible accident,which has a certain reference for the on-site well control construction.