For Drainage And Gas Production 3 1/2" Research On Structure And Technology Of Variable Diameter Plunger

The conventional plunger lifting device is not suitable for variable diameter plunger pipe columns equipped with safety valves.Therefore,with the support of CNOOC Energy Development Co.,Ltd.’s research project on offshore plunger gas lifting technology for water bearing gas reservoirs in the East China Sea,a new type of variable diameter plunger device has been developed for offshore variable diameter composite pipe column structures.The main research results of this article are as follows:(1)Design a new type of sealing structure for variable diameter plunger.Based on the composite string structure of offshore gas wells,targeting 3 1/2 The structure of the variable diameter plunger device,designed with the maximum outer diameter when the variable diameter plunger shrinks φ 68.4mm,maximum outer diameter during expansion φ 73 mm 。According to theoretical calculations,the designed variable diameter plunger structure can expand the diameter after being subjected to a certain pressure at the bottom of the well;After being hit during the lifting process,the diameter is reduced and the lifting continues through the safety valve.(2)Optimization design of sealing performance for variable diameter plunger.Using the CFD method,the pressure drop,outlet velocity,maximum gas-liquid flow velocity,resistance coefficient,and leakage rate of the sealing structure are used as optimization criteria to optimize the sealing structure of the variable diameter plunger.When the sealing groove of the variable diameter plunger is 9,the groove depth is 6mm,the groove width is 9mm,and the staggered tooth length is 8mm,the structural sealing effect is the best.A two-phase flow analysis was conducted on the expansion and contraction of the variable diameter plunger,and it was found that the lifting efficiency of the variable diameter plunger after expansion is better.The sealing performance of the variable diameter plunger is significantly improved after the installation of staggered teeth.(3)Optimize the variable diameter plunger gas lift process.Refine the parameter design steps for variable diameter plunger gas lift by considering the main influencing factors of plunger gas lift,and use vb.net software to visually program according to the parameter design steps.Bring the condition of a certain offshore gas well into the program and calculate the optimal working system for the variable diameter plunger applicable to this well.(4)Simulate the gas lift process of the designed and developed variable diameter plunger in the composite string of offshore gas wells and conduct indoor experiments.Observing the expansion and contraction of the variable diameter plunger in the composite pipe column,it was found that the variable diameter plunger can run smoothly multiple times in this structural pipe column.Simulate the relationship between the intake pressure required for the expansion of the variable diameter plunger and the liquid lifting capacity,and conduct indoor variable diameter plunger drainage and gas production tests.It is found that the variable diameter plunger can expand and lift liquid with good liquid lifting efficiency.The research results indicate that the designed variable diameter plunger device can smoothly and reliably pass through the composite pipe string and effectively discharge the accumulated liquid at the bottom of the well,providing a theoretical basis and experimental basis for the application of variable diameter plunger in offshore gas wells.