A Research On High Pressure Water Injection String Optimization

In the process of high pressure water injection in oil and gas fields,the high pressure of water injection of mouth of wellhead will make water injection string born large axial stress and bending stress.The improper design of water injection tubing string and the improper matching tool portfolio selection will lead to a packer string loss performance of tubing string,permanently damaged spiral bending of tubing string,pipe string damage and packer invalidation,etc,which can cause underground work accidents and serious economic losses.As a result,it is very important to optimal design of high pressure water injection string,to choose string combination and matching tools which adapt to the condition of high pressure water injection and to ensure the safety production of water injection string in the down hole.High pressure water injection string will be affected by piston effect,helical buckling effect,ballooning effect,temperature effect and friction effect during running process,anchoring process,setting process and water injection process.The force condition of high pressure water injection string is very complex.At first,this paper researched the high pressure water injection string and matching technology development present situation at home and abroad.Then,the paper established mechanics model of water injection string in the four basic effects which are piston effect,helical buckling effect,ballooning effect and temperature effect.After that,the paper did a detailed theoretical analysis on the force of water tubing string under different conditions and deformation of tubing string caused by stress and analyzed the force of packer.Based on the mechanical analysis of water injection string in down hole under different working conditions and calculation formula of injection string deformation,the paper programmed a water injection string optimization design software program using Visual Basic 6.0 software.The program consists of two modules,one is the load and deformation calculation module and the other is string intensity checking module.The load and deformation calculation module can calculate axial load and string deformation change of water injection string tubing caused by different effects under different wellhead pressure,different down hole depth and different working conditions such as running process,anchoring process,setting process and water injection process.String strength check calculation module can calculate external extrusion force,internal force and axial tension in different well depths,and thus for the string intensity checking.The paper did a optimization design on a injection well in the Tarim River Oil Field using this program.Calculated axial load and deformation during running process,anchoring process,setting process and water injection process and checked the string intensity.Afterwards,chose a set of down hole matching tools such as packer,hydraulic anchor and water distributor,and eventually determined a set of optimum high pressure water injection string combination process.