Research On Monitoring Technology Of Casing Deformation In Oil And Water Well Based On Optical Fiber Sensing

As one of the three traditional energy sources,oil reserves and extraction capacity have become important bargaining chips for competition among major powers in the 21st century.Steel casing is located in the outermost layer of oil and water wells,due to the influence of geological factors and mining factors,the complex underground mechanics system causes casing damage to occur from time to time.Casing damage is bending,fracture and other phenomena that occur when the force exerted on the casing exceeds its load-bearing capacity.In minor cases,oil production efficiency is reduced,and in severe cases,oil wells are scrapped,causing heavy losses to production.Therefore,through certain means to monitor the service status of the casing,especially the real-time collection of deformation variables,establish an abnormal deformation early warning and forecast mechanism,provide data support for the adoption of protective and remedial measures,ensure the safe service of the pipeline,and ensure my country’s oil production and efficiency aspect is of great significance.The paper combines the current casing deformation monitoring/detection defects such as inaccurate positioning,uncertain direction and affected by high temperature and high pressure,using optical fiber sensing technology for passive,distributed monitoring,high temperature and high pressure resistance,long life,high accuracy,and due to the advantages of electromagnetic interference,easy deployment and maintenance,the optical fiber is used as the sensing unit,and the distributed and quasi-distributed sensing schemes are compared and implemented.Through the design,mechanical analysis,and temperature and strain performance testing of the sensing optical cable,and introduce the Raman temperature measurement mechanism to compensate the temperature for strain monitoring.After testing,it is found that the temperature coefficient of the grating optical cable is 9 με/℃,the temperature coefficient of the distributed optical cable is 19 με/℃,and the accuracy of Raman temperature measurement is 0.8℃.The sensing optical cable is used to monitor the size and direction of casing deformation,using finite element software to simulate and analyze,and then simulate the installation method of oilfield casing,and build a deformation test simulation system.The test results show that the strain monitoring trends of the two sensors match the finite element analysis results.The FBG quasi-distributed sensing accuracy is higher.The strain structure of the 4-axis sensor can realize the preliminary judgment of the force direction.The curvature and bending angle of the tube are also consistent with the shape of the casing.The results of this subj ect conducted a wellbore profile temperature test in Shanxi coalbed methane.The test results are in good agreement with the traditional PLT test,and the error is within the design range.It has accumulated experience for future casing deformation monitoring in the oil field.