Research And Application Of Low-alloy Multiphase Microstructure Solid Expandable Tubular Technology

With the continuous development of oil field,the problem of casing damage of oil and water well is more and more serious,and the new problems faced by the expandable tubular workover technology are increasing day by day.The main problems are as follows:low elongation rate of the commonly used expandable tubular,insufficient working hardening capacity,insufficient effective plasticity of the remaining pipe after expansion deformation and relatively insufficient extruding strength;with the increase in the number of special working conditions,such as broken wells and high-pressure construction wells requiring repeated fracturing after patching,the original expandable tubular patching device structure can no longer meet the construction requirements of relevant special workover operations,so new expandable tubular workover tools should be developed accordingly.In accordance with the design concept of ideal multiphase microstructure steel composed of ferrite,retained austenite and a small amount of bainite/martensite,this paper selects the steel grade based on the simple composition design of the C-Si-Mn series and passes the three-step heat treatment modification process which include after isothermal air cooling（AC）,the first step of higher temperature critical heat treatment（L₁）,and the second step of lower temperature critical heat treatment（L₂）in the austenite area to control its structure and performance.The multi-phase microstructure steel which microstructure presents a multi-phase structure composed of ferrite,martensite and dispersed retained austenite is obtained.Laboratory tests show that the expandable tubular material obtained after processing of after isothermal air cooling at 900℃,lower temperature critical heat treatment at-710℃and higher temperature critical heat treatment at-670℃maintains excellent plasticity deformation and continuous processing hardening ability.Its tensile strength exceeds 700MPa,while its yield strength is less than 400MPa,at the same time,its uniform elongation exceeds 30%,elongation after fracture exceeds 41%,and impact toughness exceeds 50J.On the basis of high tensile strength and high elongation performance,the steel achieves arrives the goal of low yield strength,large expansion rate and high performance.Based on the above steel grades,for the need of the patching operation of different size casings includingΦ139.7mm andΦ177.8mm,and the patching operation requirements under different well conditions,tools such as drillable solid expandable tubular device and dredable solid expandable tubular device with bottom plug based on copper-tin alloy soft metal composite suspension seal are designed and developed.It is proved by field application that the expandable tubular patching operation device developed with this kind of expandable tubular material can effectively solve the problems of special patching operation such as the failure of the original expandable tubular patching device and the high pressure construction well requiring repeated fracturing after the patching.The success rate of the first construction of the relevant unit is 100%.On the basis of the effective replacement of the traditional liner patching technology,the technical advantages such as large diameter,high pressure resistance,non-aging and excellent sealing effect are obtained,and the rapid production after the patching repair is realized,with significant economic benefits.