Numerical Simulation Of The Bottom Flow Field In The Gas-Circulation Media

Air drilling technology has been rapidly developed and popularized now, but the research of the bottom-hole flow field is not enough as conventional drilling in most cases. Based on the theory of aerodynamic,gas-solid two-phase flow and the engineering fluid mechanics principle of the air drilling, using the model of the aerodynamic and the theory of aging model for the spaceflight aerodynamic, and with the collation of the plitting-phase model and homogeneous-phase model, one-dimensional stable state theory model of the annular air-solid two-phase flow aerodynamic which couples the flow in wellbore with the steady formation and the hole pressure is established. The model of the air drilling air-solid two-phase flow aerodynamic was solved using the finite volume numerical method. Through numerical simulation calculation, the paper analysed the distributing of the bottom-hole flow field under the situation such as different bit types and drilling rig associations, especially the changes of regular pattern of the distribution of wellbore pressure and velocity and concentration of the rock debris when two-phase flow moves up along the well-bore; Analysed the effects of the amount of air injection, drill post revolving velocity and rock debris. With summing up the regular pattern of the flow field, the optimization is made for the parameters of string assemble and drilling string rotating speed and air velocity, also for the type and design of bit is optimized.The numerical simulating chart shows that the mathematical model of annular air-solid two-phase flow is credible, and provides a basis for the further theory research and wellbore design of air drilling.