Study On The Pressure Fluctuation Mechanism Of Diversion Process For Continuous Circulation Valve Drilling System

In recent years,the development of oil and gas exploration in our country has gradually shifted to deep strata with more complicated geologic conditions and deeper water sea area,under this background,deep wells,extended reach wells and high deviated wells are more and more drilled in the development of these oil and gas fields.With the deeper depth drilled and further distance extended,the more difficulties of drilling operation encountered,the risk of downhole leaking,sticking and other downhole complications will goes up.Continuous Circulation Valve(CCV)drilling technology can maintain the continuous circulation of drilling fluid,which will benefit for solving the problems encountered in the drilling process.In a word,CCV drilling technology is a revolution in the conventional drilling fluid circulation,otherwise,the CCV drilling system in the process of diversion will appear severe pressure fluctuations,which cause damages to drilling process,which postpones the application and popularization of the CCV drilling technology.In this paper,the pressure fluctuation phenomenon of continuous circulation valve drilling system is studied,the mechanism of pressure fluctuation is analyzed,the measures to reduce the amplitude of pressure fluctuation are proposed,and the research results are as follows:(1)This paper analyzes the hydraulic characteristics of the diversion process of the CCV drilling system,and the flow relation of the normal cyclic path and the side-entry cyclic path of CCV drilling system is deduced.The relationship between the relative throttle area and the relative opening of the throttle valve is described.Compared with the tapered throttle valve,the gate throttle valve has more stable flow characteristics,which is advantageous to reduce the pressure fluctuation amplitude,and the smaller the valve resistance ratio,the smoother the relative flow change.(2)The model of hydraulic characteristic in the diversion process is established.The pressure fluctuation model of the continuous circulation valve drilling system is established,and the quantitative relationship between the pressure value at a moment of the drill pipe column and the swelling volume of the hose,the compressed volume of the drilling fluid and the compressed volume of the air section are deduced.The mathematical and physical equations of pressure both on top and beneath the CCV center valve plate are listed,and the boundary conditions are set,and the solution flow is given.(3)Based on the platform of MATLAB software,the simulation model is set up,the simulation parameters and the control parameters are established,and the simulation results are compared with field applications data in Panyu oilfield ERWs,and the simulation model is verified to be correct.Then,based on the simulation model which was established in MATLAB,the influence of different preloading pressure,hose length,throttle type and opening length on the amplitude of pressure fluctuation is analyzed separately,the control parameters are optimized and the amplitude of pressure fluctuation is reduced.The results show that the main reason which cause pressure fluctuation is the sharp decrease of flow rate,increasing the preloading pressure,narrow down the length of hose,choose gate throttle valve and prolong the throttle opening period to 10s can be reduced the pressure fluctuation amplitude effectively,which lays the foundation for the further application of the CCV drilling technology in oil and gas fields.