Packer Inapection And Corrosion Prevention Of Nitrogen Injevtion Pipe

In the later stage of oil well exploitation,there are many problems such as stratum pressure deficit and energy shortage.By injecting water or gas into oil wells,not only supplementing the stratum energy,but also improving the crude oil fluidity and recovery ratio by kinetic energy and density difference.Some oil wells in Tahe oilfield adopt nitrogen injection displacement technology,which has obvious displacement benefit,with an average recovery increase of more than 5%.However,the abnormal increase of casing pressure and tubing corrosion are often accompanied by the gas injection process,which brings great trouble to the field operation.Therefore,it is necessary to study the leakage reason and anti-corrosion of nitrogen injection gas pipe string.It is pointed out that improper sealing and anchoring of MCHR packer in tubing is one of the possible reasons for abnormal casing pressure.Based on the mechanics theory of rod and string in oil and gas wells,the force acting on the string is analyzed in this paper.The calculation results show that the pipe string is affected by the piston,temperature,bulging and helical bending effect,and the shrinkage deformation is 1.55 m.The shrinkage force produced by the deformation will be applied to the hydraulic anchor claw of packer.With the help of ABAQUS software,the simulation of setting and sealing test of MCHR packer rubber cylinder was carried out.Sealing simulation results show that the rubber drum is well compressed and in good contact with the casing after 17.2 MPa seating force is applied.The simulation results of inspection seals show that the contact stress between the rubber tube and the casing of MCHR packer is bigger than the pressure difference between the top and bottom of the rubber tube when nitrogen is injected,so the packer is well sealedANSYS Workbench is used to study the forces acting on the hydraulic anchor claw of MCHR packer under the simultaneous action of radial anchoring force and axial contracting force.The simulation results show that the maximum displacement caused by the axial force is 0.0058 mm,and the numerical value is small.It can be considered that the hydraulic anchor claw is well anchored,so the pipe string is well anchored under the condition of nitrogen injection.Comparing the casing pressure of oil pressure,it is found that the casing pressure at the dilute anti-scaling single-flow valve is greater than the oil pressure.Therefore the nitrogen leakage at the opening of the ball valve leads to abnormal increase of casing pressure and annular corrosion.Therefore,the installation position of the dilute anti-scaling single-flow valve is limited:it should be installed within 3764 m from the wellhead.This paper improves the structure of the single-flow ball valve.Installing a rupture disc above the single-flow ball valve can withstand 16.5+0.2 MPa can ensure normal casing pressure during the first round of gas injection,reduce corrosion of tubing and casing,and facilitate packer sealing.Anti-corrosion measures are put forward for nitrogen injection pipe string and packer.In order to reduce tubing corrosion,antioxidant corrosion inhibitor can be added.For the convenience of unpacking the outlet pipe,K341 long rubber packer without slip is recommended.This packer increases the length of rubber tube,not only increases the working pressure,but also fixes the string.In order to reduce the corrosion of MCHR packer,022Cr22Ni5Mo3N is recommended to be used to make the outer material of packer,which not only meets the strength requirements but also improves the corrosion resistance.