Analysis Of External Load And Failure Of Oil Casing Under Complicated Well

Under the condition of complex wellbore,in-situ stress load and distribution is very complex,resulting in the complex and variable load of the casing,which in turn causes damage to the casing.In this article we summary analysis of the complex wellbore conditions crowded load type,and compare the API collapsing formula with uniform and non-uniform in-situ stress outside casing squeezing force theory formula,and analysis of the differences between different calculation methods,summarizes the factors that influence the outside casing extrusion force from cement ring on the outside casing extrusion load and unload function,this paper provides reference for later casing intensity,so as to guarantee the safety of the casing under complex loading,prolong the life of casing.Paper is mainly to carry out the work and research results are as follows:(1)Through the analysis of research status at home and abroad,and summarizes factors,which affect the strength of casing and cement ring unloading effect,and analyses the difference between casing strength design at home and abroad,complex wellbore conditions for oil layer casing by extrusion load,as well as a variety of external cause of extrusion load and its influence factors.(2)In this paper,we analyzes the outside casing extrusion force calculation method,including API collapsing strength and uniform in-situ stress under with and without cement cement ring ring in both cases outside casing extrusion strength calculation method,calculated the cement ring on the outside casing extrusion load factors,the effect of unloading effect for behind concrete analysis provides the basis for the unloading effect of cement ring.(3)By comparing the API casing collapsing strength calculation formula of non uniform in-situ stress were analyzed and summarized in this paper the casing stress model,including one-way radial mechanical model,two-way radial mechanical model,composite mechanics model and the casing under the action of bending moment,extrusion and shear strength model,through example calculation shows that in the uniform stress under complicated loads,such as casing collapsing strength significantly reduced.(4)The finite element method is used to establish the soil-cement ring-casing force model under uniform stress condition.Combined with the calculation formula of casing outside the casing,analysis the formation poisson's ratio and elastic modulus,poisson's ratio of cement ring,elastic modulus,thickness,cement and casing ring defects in medium under the condition of uniform in-situ stress of casing and cement ring the influence law of unloading.(5)Establishing the uniformly distributed load and shear loading finite element mechanical model,combined with the compound formula of casing collapsing strength under load,comparing with and without cement ring cement annulus condition condition of casing collapsing ability influence law,including the formation non-uniform degree,the moderate,casing pipe size and influence factors such as cement thickness and under the condition of uniform in-situ stress analysis of casing cement ring shear load.(6)The casing failure analysis.Research in each casing failure situation,in view of the casing collapse,shear failure situations,such as selecting a typical failure of the casing damage Wells,combining with the previous formula and finite element analysis theory and as a result,to analyze the reason of casing failure.