Wellbore Stress Distribution And Casing Safety Evaluation Based On Wellbore Integrity

At present,the wellbore integrity concept and its position in oil and gas well management are gradually being taken seriously.The concept of oil and gas wellbore integrity was first applied to foreign oil and gas field management.From the statistical analysis of the integrity failure of the wellbore,the casing failure is the main factor leading to the failure of the wellbore integrity.Based on the concept of wellbore integrity,this paper considers the main risk factors of casing failure based on the single factor study of the wellbore.A risk assessment model for casing failure in horizontal well sections was established,and then a safety assessment method was selected to conduct a risk analysis of the wellbore integrity model.Firstly,this paper determines the stress distribution of formation stress and near wellbore area through literature review and field experience data,and then determines the wellbore and casing load calculation model to provide reference for wellbore strength analysis.Secondly,considering the influence of the properties of the casing around the wellbore,the load is a changing process for a certain period of time.According to the elastic layer mechanical model of casing confining pressure,combined with the viscoelastic mechanical model,the mechanical model of casing dynamics of viscoelastic surrounding rock is established,the variation law of casing confining pressure is analyzed,and the physical properties of formation cement ring are analyzed for viscous surrounding rock.The influence law of the casing confining pressure.Thirdly,the three-dimensional finite element model of the wellbore including the casingcement ring-stratum is established by computer software,and the factors affecting the strength of the casing string and its influence law are analyzed.Mainly consider the main risk factors and the risk factors that may occur during the fracturing process.The properties of the stratum mainly analyze the influence of the inhomogeneity coefficient of the ground stress,the mechanical parameters of the stratum and the defects of the stratum.The cementing quality includes the influence of the cement ring and the mechanical parameters of the cement ring.Casing factor analysis of the influence of casing wall thickness on casing strength.Based on the above analysis results and its curve regularity diagram,it provides a reference for the casing risk assessment in the subsequent risk assessment of wellbore integrity.Finally,based on the fuzzy comprehensive evaluation method,combined with the analytic hierarchy process.A wellbore integrity analysis model is established to determine the weight values of each level factor,and the fuzzy mathematics operation method is used to determine the membership degree of the evaluation factors at all levels.The risk value of each factor is finally determined and the risk value of the total target wellbore integrity in the evaluation model is determined.It provides certain reference significance for wellbore integrity management in horizontal well fracturing operations.