Study On Mechanical Behavior And Sealing Performance Of Integrated Pipe String For Gas Well Fracturing And Commissioning

With the development of oil and gas fields into the middle and late stages,some oilfields need to maintain productivity by exploiting low permeability and ultra-low permeability gas reservoirs.Fracturing modification is an effective measure to improve oil recovery in low permeability and ultralow permeability gas reservoirs.Fracturing and production integration string of gas wells can simplify construction process,reduce construction cost and reduce reservoir pollution,which has popularization value.Special threaded joints are the key components of gas well fracturing and production integration string,which play an important role in the sealing performance of the string.However,during the process of fracturing and production,the joints undergo load changes and erosion wear,and the strength and sealing performance are greatly affected.Therefore,it is necessary to study the strength and sealing performance of typical special threaded joints of gas well fracturing production integration string before and after fracturing under complex stress and erosion wear conditions,which can provide theoretical guidance for the design and application of gas well fracturing production integration string.In this paper,the mechanical behavior and sealing performance of gas well fracturing and production integrated string in Daqing Oilfield under different working conditions were studied.Based on the basic theory of pipe string mechanics and beam-beam contact theory,a finite element analysis model of variable cross-section friction contact of pipe string was established.The deformation of pipe string in a practical production well in Daqing Oilfield was numerically analyzed,and the reliability of the numerical analysis results was verified by magnetic positioning data.The mechanical behavior of the integrated tubing string of production wells in Xushen Gas Field of Daqing Oilfield under different working conditions was analyzed by finite element method,and the variation law of the stress and deformation of the integrated tubing string under the conditions of drilling and completion,shutin,sealing,well opening and fracturing was obtained.Laboratory tests on erosion and wear of integrated tubing were carried out on a rotating erosion and wear test rig.The variation of erosion and wear rate of 2-7/8 TBG tubing under given conditions was obtained.A numerical model of erosion wear rate of tubing string was established.The erosion wear of 2-7/8 TBG tubing and 3-1/2 TBG tubing under different conditions was numerically analyzed.The wall thinning speed under different displacement and sand ratio conditions and the wall thinning amount under different fracturing conditions were obtained.The sealing structure of typical threaded joints of integral pipe string was analyzed,and the calculation method of upper buckling torque of special threaded joints was established.The shape measurement of three typical special threaded joints of an integrated pipe string was carried out,and the finite element model of the joints was established and revised.Through the finite element analysis,the variation of connection strength and sealing performance of three special threaded joints under different loads such as buckling torque,axial tension,axial pressure,bending,internal pressure and external pressure before erosion was obtained.Considering the extreme erosion wear,the strength and sealing performance of three threaded joints under production and fracturing conditions were analyzed by finite element method.The failure modes and failure loads of special threaded joints of integral tubular columns before and after erosion wear were analyzed under single and compound loads.The possible failure modes and critical loads of different threaded joints were obtained.According to the safety analysis of fracturing and production conditions,the applicability of three special threaded joints in the integrated pipe string was obtained.