Research On The Integrity Of Special Threaded Joints Of Casing

With the consistent development of oil&gas advanced techniques,various advanced wells are growing rapidly including extreme temperature&pressure wells and ultra-deep wells,which have caused the problem that traditional API connections can barely meet the current needs of oil fields.And the consumption of premium connections is increasing gradually which can significantly enhance the casing sealing performance and has a good reputation in oil fields.However,there still remains some concerns such as thread gluing,tripping and damage on sealing surface,which indicates that it is urgent to research on material optimization.This thesis systematically applied the methods of laboratory experiments and finite element to analyze the factors affecting the integrity of different premium connections by different load conditions which can provide references for the optimization of premium connections in oil fields.The specific research contents are as follows:(1)Survey and analysis of characteristics of typical premium connections.The current situation of the theory,finite element and experimental research on premium connections of casing has been investigated at home and abroad,through which we can get the characteristics,advantages and the main influence factors on integrity of premium connections.(2)Optimization and evaluation of premium connection material.The variation laws of yield strength,tensile strength,corrosion rate affected by temperature have been studied through the experiments of stretching in extreme temperature and gravity loss under corrosion which confirmed material selection to protect the integrity of premium connection under high temperature and high pressure,and also provide key parameters for calculation of finite element.(3)Study on full size experimental stress field of premium connection under multiple loads.The torsion-circle curve and stress-strain law in the processing of makeup and breakout were obtained through experiments which have proved the model of finite element;the laws of stress-strain and collapse failure under the affecting by non-uniform load are obtained through the collapsing experiments which can provide the experimental data support for the integrity research of premium connection;the extrusion strength of premium connection is higher than it of casing comparing to the casing collapsing experiments;the stress-strain law of premium connection under axial compression load was obtained through the axial compression load experiments which have been proved that the axial compression resistance of premium connection can meet the needs of oil fields.(4)Research on influential factors of various sealing structure of premium connection integrity under multiple loads.The finite element’s mechanical models of conical surface to conical surface and cylindrical surface to spherical surface are established.Sealing performance and connection performance of premium connection under the combination of axial force,internal pressure,axial tension,external pressure are systematically studied by numerical simulation method.The influence law under different load conditions of the premium connection integrity was obtained,and comparing two kinds of spherical surface.Focus on the complicated downhole conditions,the key factors affecting the integrity of premium connection were found from the optimization of premium connections.The factors that affected the integrity of premium connection by pipe properties,axial forces,non-uniform external loads,sealing surface structure and internal and external pressure are studied,which provides guidance for the selection of premium connection in oil fields.