Study On Finite Element Analysis And Defect Detection Methods Of Pulsed Eddy Current Testing For Multi-layer Tubular Structure

In recent years,with the rapid development of social economy,the demand for oil and gas energy is increasing day by day.In order to ensure the safety of oil and gas collection operations,non-destructive testing methods are applied to evaluate oil and gas well collection system.Pulsed eddy current testing has attracted much attention in the detection of structural defects in oil and gas wells because it is not affected by non-ferromagnetic interference and has a fast detection speed.In this thesis,based on relevant scientific research projects and actual requirements of oil and gas well engineering,the numerical simulation based on finite element analysis and defect qualitative and quantitative analysis methods of multi-layer tubular pulsed eddy current testing are studied.And then the method of distinguishing and classifying typical defects is studied.Furthermore,quantitative analysis method is studied to obtain the minimum casing inner diameter.The main research work and innovations of this thesis are as follows:(1)In this thesis,based on the complexity of analyzing pulsed eddy current response and the weakness in the detection principle of multi-layer tubular structure defects in oil and gas wells in various typical scenarios,the numerical simulation modeling method based on finite element analysis is studied.For typical defects such as:transverse crack,longitudinal crack,bending deformation,extrusion deformation,etc.,as well as the probes in the three directions used in the actual test,single-layer casing longitudinal probe model,single-layer casing lateral probe model,tubing+casing longitudinal probe model are designed.The numerical simulation method based on finite element analysis is used to analyze the response signals and spatial electromagnetic field distribution.The detection ability of probes in different directions is analyzed in different scenarios of different types of defects.The characteristics of detection signals and distribution of magnetic fields are summarized which provides support for qualitative and quantitative analysis of defects in multi-layer tubular structures.(2)Based on the conclusions of numerical simulation modeling research,the qualitative analysis method for multi-layer tubular structure defect detection in oil and gas wells is studied.And more than ten typical defects of oil and gas well multi-layer tubular structures are identified and classified.In order to eliminate the baseline drift phenomenon of the multi-layer tubular structure detection signal of oil and gas wells,the method of baseline removal based on piecewise least squares method is proposed.Based on the characteristics of the numerical analysis,the principal component analysis method is improved to extract features used for qualitative analysis Furthermore,based on the extracted features,the qualitative analysis using the random f-orest classification method is used to identify and classify the def,ects of multi-layer tubular structures which achieves good results in the experiment of single-layer casing and tubing+casing detection scenarios.At the same time,compared with the traditional principal component analysis method,the improved principal component analysis method proposed in this thesis obviously improves the qualitative classification accuracy and has stronger qualitative analysis ability.(3)In order to obtain the minimum casing inner diameter,a quantitative analysis method for the detection of multi-layer tubular structure defects in oil and gas wells is studied.Based on the qualitative analysis of multi-layer tubular structure defect detection in oil and gas wells,a feature extraction method based on combined features is proposed.Furthermore,the quantitative analysis using the random forest regression method is used to analyze the minimum casing inner diameter of multi-layer tubular structure defects which achieves good results in the experiment of single-layer casing and tubing+casing detection scenarios.At the same time,compared with the analysis method based on non-combined features,the quantitative analysis method based on combined features in this thesis obviously improves the quantitative analysis accuracy and has stronger quantitative analysis ability.In summary,in this thesis,focusing on the practical requirements of pulsed eddy current testing for multi-layer tubular structure defects in oil and gas wells,the characteristics of pulsed eddy current testing,qualitative discrimination method and quantitative evaluation method in typical scenes are studied.More than ten typical defects are qualitatively discriminated and the minimum inner diameter of the multi-layer tubular structure is quantitatively analyzed.A technical solution of pulsed eddy current testing is proposed including numerical simulation,qualitative evaluation and quantitative calculation,which provides technical support for the health status evaluation and life prediction of the multi-layer tubular structures of the oil and gas well.