Study On Stress Distribution In Casing Under Coupling Condition Of Stratum And Cement Ring

Cementing provides oilwell production with safe channel, which consists of casing and sheath as well as formation, however conditions with different kinds of formations and sheaths have effects on the distribution of casing stress, which is bad for the safety of oilwell production. So, based on formation-sheath-casing coupling system as well as previous related theories, this paper studied the distribution of casing stress, what the paper did mainly were as the following:Depending on the plane-elastic stress theory, the paper based on the coupling formation-sheath-casing model, and resorted to the finite element software ABAQUS to analyse the effects on the distribution made by formation parameters and sheath parameters in sequence, including formation and sheath elasticity modulus and poisson ratio, uniformity coefficient of formation stress, ovality and lackage of sheath as well as casing eccentricity, and the disciplines of each factors’effects on the distribution of casing stress were attained.Based on the analysis on single factor’effect on the distribution of casing stress, the paper analysed the distribution in case of united force from uniformity coefficient of formation stress and sheath parameters as well as the wellbore ovality, and the relevant displines were gained.The parameters of formation and casing is hard to be changed when wellbore is finished, but cement sheath is formed from the cement slurry, which is chosen with much more choices; cause sheath elasticity modulus has the similar effect on the distribution to sheath poison ratio. So, in order to simulate the complicated condition casing exsits as comprehensively as possible in realistic well settings, based on coupling model with1.6uniformity coefficient of formation stress,1.08ovality ratio and0.4lackage ratio, the paper analysed the effect of sheath elasticity modulus on the distribution with different formation elasticity modulus and casing eccentricity. According to the formation elasticity modulus, three types of formation were classified, high elasticity modulus formation, middle elasticity modulus formation and low elasticity modulus formation, when oilwell is built in different type of formation, the relevant rules of the effect of sheath elasticity modulus on the distribution were attained, as well as the range of sheath elasticity modulus.Cause of the intricate condition in wellbore, the FEM simulation aided by ABAQUS makes the simulation of the distribution more comprehensive and easier, which plays a guiding role in optimizing the distribution of casing stress.