Experimental Study On Gas-liquid Two Phase Flow In Bull-heading Well Killing

The study on the law of gas-liquid two phase flow under inverse condition is the key to the solution of the fluid mechanics calculation and the calculation of well parameters in the wellbore during the bull-heading well killing process.In this process,the velocity of liquid phase is downward,while the direction of free drift of gas under the action of buoyancy is opposite to the direction of liquid flow,and few scholars have made full research on this problem at present.It is important to study the gas-liquid two phase flow law under this working condition for improving the unconventional well killing control theory.It is of great significance to the safe,rapid and economical drilling of oil and gas reservoirs assurance.In this paper,a vertical,visual and large diameter experimental device for gas-liquid two-phase flow research under inverse condition is designed and reconstructed.Experimental research and theoretical analysis of the two phase flow under this condition are carried out based on this device.The conclusions are as follows:The flow pattern of gas-liquid two phase flow is divided in detail by designing the experiment of conversion mechanism.The flow patterns of inverse two phase flow are divided into four flow patterns: bubbly flow,projectile flow,slug flow and churn-turbulent flow.The characteristics of two phase flow in each flow pattern are analyzed,and a more detailed flow pattern of two phase flow is established by comparing with the previous research results.Based on the theoretical and experimental results,establish the criterion for the flow pattern transformation of bubbly flow-projectile flow in a vertical tube under the inverse condition.By comparing with the experimental data,it is proved that the error of the flow pattern conversion prediction model is within 5%.Compare the theoretical calculation results of hold-up and experimental measurement results of bubble flow and projectile flow.A linear relation between the void ratio and the Froude number is found and establish the drift velocity model in projectile flow.According to the definition of critical well displacement in this paper,the critical well displacement in different gas phase displacement conditions is obtained through experimental study.Analyze the rule of critical well displacement with gas phase displacement.When the superficial velocity of gas is less than 0.062m/s,the critical well displacement increases rapidly with the increase of gas displacement,and then keeps stable.Based on the experimental data of critical well displacement,the empirical formula of critical well displacement for pressure recovery is established in this paper.Through the sensitivity analysis,the influence of the different well diameter conditions on the displacement of the critical well is obtained.