Optimal Design And Simulation Of Stator And Rotor For Downhole Turbine Generator

Downhole MWD/LWD tools are key skills for oil and gas drilling. There are two major power supplies for downhole MWD/LWD tools which includes lithium-ion battery pack and downhole mud turbine generator. Compared with lithium batteries, turbine generator has more advantages. It can work properly under high temperature and high pressure. It is anti-wear and doesn’t have to replace frequently. With these advantages, turbine generator becomes to be widely used in oil exploration. The paper mainly discussed design and modeling of key components of high power downhole turbine generator. This included mesh generation of its rotor and stator and their flow field simulation. According to results from numeric simulation on ANASYS/Fluent, mechanical structure of stator and rotor was optimized, and downhole performance of mud turbine generator would be improved. The main research contents and results were as follows:(1) In the second chapter, MWD wireless logging system was introduced, and overall structure of mud positive pulser was built. The second chapter mainly discussed design of downhole turbine generator. According to the basis of rotating blade shape and its design theoretical principles, mechanical structure of blades for both stator and rotor was designed. For stator, the mean line was composed by three curves, ant its blades were made with the same thickness. For rotor, it was made with two kinds of blade structure: constant thickness with constant pitch and variable thickness with constant pitch. Besides, manufacturing material of downhole turbine generator was analyzed and selected on the basis of its working condition and requirements.(2) In the third chapter, characteristics of mud flows were analyzed, and numbers represent mud as high Reynolds fluid were calculated. With mud Reynolds characteristics, numeric simulation model for downhole turbine generator was built and its numeric solution was set. The major part was CFD mesh generation and simulation conditional processing. These included assumptions of turbine generator working environment and settings of Fluent simulation relevant parameters, such as fluid model, fluid material, related boundary conditions, solution solver and solving methods.(3) Models of stator and rotor were built via Pro/E and Solid Works, and their computational domains were divided. Based on computational fluid dynamics software, ANSYS/Fluent, flow field of stator and rotor was simulated. Numeric simulation results were generated such as axial forces, moment of blades, static pressure within turbine generator and theoretical power of rotor. According to these results, structures of stator and rotor were optimized. These included blade numbers, blade thickness, outlet angle of stator, outlet distance of stator and helix angle of rotor.(4) Influence of distance between stator and rotor and impact of flow rate of mud was analyzed. According to numeric results and graphs of CFD-Post, the whole design and flow rate was optimized.