Numerical Simulation And Experimental Research On The Working Mechanism Of The Pressure-controlled Drilling Choke Valve

When using conventional drilling equipment and methods to deal with pressure decay,narrow window density,high temperature and pressure,high permeability fractured reservoirs,many complex drilling problems will happen,such as well kick,well leak,harmful gas leaks,sticking,too long tripping time and so forth.MPD-Managed Pressure Drilling gradually develops to solve such complex technical drilling issues in recent years.It is based on the effective control of down-hole pressure.The MPD greatly improve the drilling speed,shorten the drilling cycle and make drilling operations safer.The choke valve is a key component to achieve pressure control in Managed Pressure Drilling Systems.It directly contacts with slurry and controls the pressure of wellbore.So,its main performance parameters and pressure control characteristic curve directly affect the success rate of implementation.Namely,a kind of high precision,reliability and long life MPD choke valve is undoubtedly not only a strong guarantee for successful implementation of MPD technology,but also a solid foundation for the promotion of MPD technology.So,this paper did research about the working mechanism of the MPD choke valve,the main works carried out as follows:(1)Study on using state of MPD chokes valve and investigation into Operating Characteristics of some other kinds of existing choke valve.Some details about existing choke valve,such as using state,functional and performance requirements were mastered by literature and field research.Besides,a better Valve seat and plug structures were selected by evaluating pressure control affect,the flow field characteristics and resistance to erosion capacity and service life.(2)The studies on new choke characteristic of MPD choke valve and liquid-solid two-phase fluid dynamics theory.The study aims included linear relationship between opening degree and choke pressure(L-AP)and well anti-erosion ability.That is,relationship among MPD choke valve opening degree,choke pressure and flow mass were well researched based on Computational Fluid Dynamics and domestic and abroad erosion theory.Besides,distribution of fluid flow field in valve chamber as well as MPD choke valve erosion rate in the liquid-solid two-phase flow and the movement of debris were also considered.(3)Choke characteristic and erosion Numerical Simulation of the new MPD choke valve.Firstly,the new MPD choke valve's flow field distribution and erosion laws under different conditions of liquid-solid two-phase flow were studied by computational fluid dynamics numerical simulation methods.Then,comparison among numerical simulation results,theoretical results and real results were made.Lastly,proposed improvement programs and verified the feasibility of the improvement.(4)Experimental study on the new MPD choke valve.According to the theory to design experiments equipment,two different kinds of experiments were done.One is to verify the linear relationship between opening degrees and choke differential pressure(L-?P);another one is to probe anti-erosion ability of different material and PVD coating progresses.By combination of theoretical analysis,numerical simulation results and experimental results,some design flaws were found and the direction of improvement and optimization were also determined.In a conclusion,the research provides a reference to optimize and use choke valve and of course,it has some certain social and economic significance.