Research On Optical Fiber Temperature And Pressure Sensor In Oil And Gas Well

As one of the important technologies in the sensing field,optical fiber sensing has gradually become the research object of many researchers due to its small size,light weight,wide application environment,and easy distributed networking.Temperature and pressure are important sensing parameters,and their monitoring in some harsh environments becomes particularly important.For example,in the process of underground oil and gas wells,the temperature can reach 300℃,and the pressure can reach more than 100 MPa.In these environments,therefore,traditional electronic sensors are difficult to test stably for a long time.Based on the fiber grating and the material properties of carbon fiber materials,in this paper,we build a temperature and pressure sensing system that can be used in the high temperature and high-pressure complex environment of oil and gas wells.The specific research contents are as follows:First,this dissertation reviews the current research status of fiber grating temperature and pressure sensing technology,including some traditional structures and research progress of fiber optic sensors in temperature and pressure measurement,briefly analyzes the advantages and disadvantages of various methods,and points out that fiber optic sensing technology is used in oil and gas wells,and it’s application prospects in harsh environments.Afterwards,a theoretical analysis of the fiber grating temperature,pressure and strain sensing principles is carried out,and the solution to the cross-sensitivity problem is outlined.At the same time,several fiber grating processing methods are explained,and the package structure is theoretically analyzed.Then we set up a temperature and pressure sensor test system,which can conduct experimental research in the range of 0-300℃ and 0-200 MPa,and we use the material properties of carbon fiber to conduct packaging research on fiber gratings made by femtosecond lasers.The carbon fiber sheet is assembled layer by layer with high temperature resistant epoxy resin to form a carbon fiber block,and the fiber grating is encapsulated in the carbon fiber block to form a pressure sensor.The temperature pressure test is performed on it,and the temperature sensitivity is found to be between20-30 pm/℃.At room temperature,the pressure sensitivity is about-20 pm/MPa,and the pressure sensitivity gradually decreases as the temperature increases.Finally,a pressure sensor based on carbon fiber tube sensitization is re-designed and proposed.The pressure sensor is realized by using a three-dimensional and fourdirectional weaving method to weave carbon fiber filaments into a tubular structure,and by being cured to form a composite carbon fiber tube through high temperature resistant epoxy resin.The two sides of the carbon fiber tube are encapsulated to form a hollow structure as an elastic body to form the skeleton of the sensor,and the surface is embedded with a high temperature resistant fiber Bragg grating as a pressure sensing element.By adding a temperature compensation grating,the simultaneous measurement of oil and gas downhole temperature and pressure is realized.The experimental results show that the pressure sensor can work in the environment of 0-150℃ and 0-80 MPa,and the pressure sensitivity is different at different temperatures,and its pressure sensitivity can reach-50.02 pm/MPa,and it shows a good linear fit.The pressure sensor can better solve the cross-sensitivity problem in the temperature and pressure test process,meet the accuracy requirements of downhole production,and provide an experimental basis for the design of the downhole high temperature and high-pressure optical fiber sensor.