Study On Design,Preparation And Corrosion Behavior Of Soluble Aluminum Alloy Tubing

The fracture-cavity type reservoir in Xinjiang Tahe Oilfield has the characteristics of"buried depth,high temperature,easy leakage,and long open-hole interval",etc.It is necessary to adopt layered acid fracturing completion technology to extract oil.Due to the failure of the packer to unseal and the collapse of the well wall,it is easy to cause the steel pipe column to be stuck in the production stage.Workover is difficult,expensive,and has a low success rate.Therefore,it is hoped that the open-hole completion tube and packer are designed as soluble materials to achieve effective isolation during completion and to dissolve in the high-temperature formation water environment during later production.This article attempts to select aluminum alloy pipes that can be dissolved in high-temperature formation water environment.First,based on high-temperature loads and allowable dimensions,select the aluminum alloy grade of the pipe and calculate the wall thickness of the pipe,and perform simulation load test to verify it.Then for 4 hours of high temperature,high pressure and strong acid operation,the aluminum tube(inner wall)is surface treated,and simulated acid resistance test.Finally,the corrosion behavior of aluminum alloy pipes(outer walls)based on temperature,pressure,and time in saturated brine was systematically studied.Provide theoretical and application support for the actual development of tubing.2024 aluminum alloy,which is light-weight,high-temperature strength,poor corrosive,and drillable,was selected as the material of the tubing.An oil pipe with an outer diameter of 110 mm,a wall thickness of32 mm,and a length of 3 m was prepared by a fixed core extrusion method.Static mechanical tests at 160°C show that the yield strength of the tubing is stable at about 330 MPa and the tensile strength is stable at about 450MPa.According to the strength and completion size requirements,the size of the designed tubing is theoretically calculated to be 101.6 mm outer diameter and 10 mm wall thickness;simulation The actual working condition test shows that under the combined loading conditions of tensile force of 60t,internal pressure of 50MPa,and temperature of 160?,no deformation of the oil pipe with a wall thickness of 10mm or 15mm occurs.Three high-temperature and acid-resistant surface treatment methods were selected:electroless Ni-W-P plating,micro-arc oxidation+thermal spray polytetrafluoroethylene,and silver plating.The experimental results at 100°C and 20%hydrochloric acid showed that the quality of the test piece lost only about 1%after 4 hours of the electroplated silver and micro-arc oxidation+thermal spray polytetrafluoroethylene surface coating.Verification experiments of simulated actual working conditions of electroplated silver pipes show that under the conditions of 100°C,30MPa,and 20%HCl,the quality of the test piece loses only about 0.5%after 5hours.Electroplated silver can be recommended as a surface treatment technique for actual tubing preparation.The results of weight loss of 2024 aluminum alloy in saturated brine under different temperature and pressure conditions show that uniform corrosion has a strong dependence on temperature.The higher the temperature,the more severe the uniform corrosion,but as the corrosion time increases,Corrosion will gradually slow down and eventually reach a stable value.Uniform corrosion is dependent on pressure.The larger the pressure,the more severe the uniform corrosion.As the corrosion time increases,the influence of pressure on uniform corrosion changes.As the pressure increases,uniform corrosion increases first and then decreases.In comparison,temperature is the main factor affecting the weight loss of corrosion.It is estimated that it takes about 3 years for the aluminum alloy oil pipe with an outer diameter of 101.6mm,a wall thickness of 10mm,and a length of 9.5m to completely degrade under actual operating conditions.At different temperatures,Potentiodynamic polarization curves of the2024 aluminum alloy immersed in saturated saline for a long time showed obvious"inflection point",and the material was passivated.The higher the temperature,the faster the passivation occurs,but the larger the corrosion current.The corrosion rules at 25°C and 80°C are the same.At the initial immersion time(within 24 hours),the corrosion current is very small.With the extension of the immersion time,the corrosion current gradually increases and the corrosion intensifies.The fitting results of the electrochemical impedance spectroscopy test of the 2024 aluminum alloy immersed in saturated saline for a long time at different temperatures show that in the initial immersion(within 24 hours),the dense passivation film is formed and plays a role in inhibiting corrosion;With the extension of the immersion time,the outer passivation film ruptures,and the inner layer forms a new film layer,which continues to play a physical barrier to inhibit corrosion.The damage of the outer passivation film at 80°C is stronger than 25°C and the reblocking effect of the inner layer of the passivation film is also weaker than 25°C.XRD and XPS analysis results show that the outer layer of the passivation film is mainly alumina,and the inner layer is mainly Al(OH)₃ and AlOOH.