Research On The Dynamic Response Analysis Of Wellbore Pressure In Choking And Killing

Engineering practices suggest that the choking and killing technology is an effective method to handle the well control issues in permeability reservoirs(such as sandstone reservoirs),which usually have large safety drilling windows.However,in recent years,this technology has been reported with many cases of failure for dealing with the kick issues in the pressure-sensitive reservoir(such as fractured reservoirs),which are endowed with narrow drilling windows.In addition,with the increase of the failure cases,the cases of erosion damage to the wellhead device are also increased due to the long-time erosion with the high-speed sand-containing gas flow in open-flow,which has become a potential risk affecting the safety of well control.The analysis shows that,in order to ensure the success of choking and killing operation in pressure-sensitive reservoirs,it is necessary to improve the accuracy of pressure control.In order to avoid the potential risk of well control safety,it is necessary to evaluate the erosion damage of wellhead in real time.However,there are mature solutions for these problems yet.The difficulty of solving the above problems is that:1)the initial state of the wellbore is unknown,there is neither a complete mathematical model nor a corresponding calculation method;2)the dynamic behavior of wellbore pressure in choking and killing is unknown,there is neither a complete mathematical model nor a calculation method of unconventional dynamic boundary;3)the erosion damage of the wellhead device in open-flow is unknown,and there is neither a complete mathematical model nor a finite element numerical simulation method.Therefore,this paper systematically carried out the following research works,the inversion of the initial state of the wellbore,the dynamic response of wellbore pressure,and the simulation of erosion damage of wellhead in open-flow and choking and killing.According to the law of gas-liquid two-phase flow,the physical model and mathematical model of the initial state of the wellbore were established.The inversion method of the mathematical model was presented,which can accurately reflect the initial state of the wellbore and provide a solution for the calculation of wellbore initial state.The results show that the mathematical model and the inversion method are precise enough to describe the actual situation.According to the theory of gas-liquid two-phase flow,the physical model of wellbore and the mathematical model of dynamic pressure response in choking and killing(the overflow mixture is migrated or discharged along the annulus to the wellhead)were established.Besides,it determined the unconventional dynamic boundary of the mathematical model.Aiming at the problem of the unconventional dynamic boundary,a computational method of a mathematical model for calculating the dynamic pressure response is proposed.Based on the finite difference principle,reasonable meshing method and stepwise iteration are used to determine the dynamic response of casing pressure in choking and killing.It successfully solved the calculation problem of the unconventional dynamic pending boundary.Based on the calculation method of dynamic pressure response in choking and killing,the calculation results are compared with the measured data of the experimental wells,which proves the reliability of the mathematical model and the calculation method.Therefore,they can be used to implement the accurate control of wellbore pressure.Based on the calculation method of dynamic pressure response in choking and killing,the influence factors were analyzed.The results show that the influence of the volume change on the time of the maximum casing pressure is obvious;the composition change of the overflow has a certain effect on the maximum casing pressure,and a reasonable casing pressure can effectively suppress the phase transition behavior of the overflow at the near-wellhead section.Based on the erosion theory of gas-solid two-phase,the erosion model of wellhead device in open-flow was established.The numerical simulation of the erosion damage of the wellhead was performed carried out with Fluent.The reliability of the mathematical model of erosion damage is proved with the comparison of the experimental data.In this paper,system theory and methods were applied to optimize various subsystems and build an integrated well control system.With a view to achieving the purpose of ensuring the safety and success in choking and killing,which means a great practical significance to solve the critical problems that seriously affect the well control safety.