Failure Analysis And Measures To Improve Performance Of Casing String

In oil drilling and later oil extraction process casing plays an important role,poor choice will lead to various forms of casing failure.The core performance of casing is its collapsing-resistance,which is vital to maintain the stability of casing.At present,calculating the casing strength mainly use the API method.The main problem of the standard is too conservative and can not reflect the different manufacturers,different quality and intensity between casings.It also brought many problems in casing design and appliaction.Therefore,the establishment of casing products to reflect the strength of the casing strength calculation is necessary.Based on this,this paper focuses on the process casing,casing collapse resistance properties and the design of the casing string,the completion of the work,is as follows:(1)In order to improve the processing quality of casing,casing process is improved,including improving casing thread machining accuracy,improving the painting quality of the end products and strenthening the monitor to on-sites.(2)In this paper,on the basis of a summary of the calculation method of collapse strength taking into account manufacturing defects in the pipe of domestic and abroad,Casing collapse calculation model is put forward in geometric imperfections,axial load and non-uniform external loads respectively.And collapse calculation model of casing containing geometric imperfections is proposed in composite loads.Finite element software were used to verify the proposed or selected casing strength calculation models.(3)Trixial stress model of casing strength is deduced,and axial foree,external pressure and internal pressure distribution along well depth are calculated according to the well type and the casing type.The intensity of the casing string theory is established according to improved other safety factors.That is,casing type is selected according to the collapse strength of casing firstly,and then checking the casing through the tensile and compressive strength,so the casing is selected to meet the requirements.If the tensile or compressive strength within does not meet the safety requirements,it needs to choose the casing strength design.On the basis of the design of the casing string,casing string design application software is established using Visual Basic software,the application software has a friendly interface and has the characteristics of a simple operation.