Numerical Simulation Study Of Casing Stress Analysis And Stress Distribution Under Fracturing Conditions

The horizontal well fracturing technology can release the oil and gas resources that were difficult to extract,but it also brings more serious casing damage and deformation problems.The casing damage and deformation problem severely restricts the oilfield development process and seriously affects the normal production of the oilfield.In this article,we use a combination of theoretical analysis and numerical simulation to study the casing damage in X oilfield under fracturing conditions,and provide a theoretical basis for the normal development process of X oilfield.The specific research results are as follows:(1)Through researching a large amount of domestic and foreign literature,starting from the phenomenon and characteristics of casing damage,and combining with the actual site in the study area,we summarized and analyzed the casing damage factors from two aspects:geological factors and engineering factors,and carried out theoretical and numerical simulation studies on casing damage from the above two aspects.(2)In order to better understand the effect of complex loads on casing under fracturing conditions,the paper firstly idealizes the complex load problem and establishes an analytical model of casing forces under uniform loads,which is then used as the basis for studying the uneven load problem.On the basis of the force model of casing under uniform load,calculations and analyses were carried out,and the analytical curves affecting the resistance of casing to external load were plotted.The conclusion shows that the wall thickness of the casing and the modulus of elasticity of the cement ring have a significant effect on the casing resistance to external load,compared to the thickness of the cement ring which has less effect on the casing resistance to external load.(3)In order to be closer to the problem of casing damage in oil wells in practice,based on the idealized treatment of casing subjected to uniform load,a calculation method for casing stress and strength under non-uniform external load is proposed by model simplification of nonuniform load distributed in the outer ellipse of casing,and combined with the actual field practice,the calculation of the external load non-uniform coefficient based on the ground stress at the location of casing damage of casing damage wells in the study area is carried out,and the results are obtained The results are as follows: Under non-uniform load conditions,the maximum load that the casing can withstand decreases rapidly and is on average about 12.6%of that under uniform load.(4)A simple casing shot mechanical test experiment was conducted to address the issue that the casing strength at the shot hole may be significantly reduced after casing shot hole during fracturing development.In the study,it was found that the strength of the casing after injection was 88.22%-88.44% of that of the original casing by taking the injection method in the study area.Based on the casing shot-hole mechanics experiments,a three-dimensional analysis model of casing-cement ring-formation under fracturing conditions considering spiral shot-hole was established using ABAQUS finite element software.The influencing factors such as formation elastic modulus,formation Poisson’s ratio,formation stress difference,formation slip,cement ring elastic modulus,cement ring thickness,fracture construction displacement,and fracture construction pressure were analyzed numerically respectively.And the influence law of casing force and deformation was obtained.