Research On Optical Fiber Sensing Technology For Integrated Measurement Of Temperature And Pressure

Fiber optic sensors have been widely used in many fields,such as building bridges,biomedicine,petroleum and petrochemical and so on.In recent years,we have gone deep into all aspects of industrial production with the ever-changing development trend.This paper addresses the high temperature and pressure environment in oil wells,researched a temperature and pressure integrated dual-parameter optical fiber sensing system using fiber grating and Fabry-Perot(FP)resonator cascade structure.The main research contents include the following four aspects: basic theory and sensing principle of temperature and pressure sensors;fabrication,packaging and performance optimization of temperature and pressure sensors;analysis and processing of temperature and pressure sensing signals;and high temperature and high pressure test of temperature and pressure sensors.First,this article reviews the history and development of optic fiber sensors.The research and application of temperature and pressure dual-parameter fiber-optic sensors at home and abroad have been investigated,and the application prospects of downhole temperature and pressure sensors for oil wells have been described.Second,according to the special structure of the sensor proposed in this paper,the basic principles of the fiber grating and FP pressure sensors are analyzed,and the sensing principle of the fiber grating as the temperature-sensitive unit of the temperature and pressure sensors and the FP cavity as the pressure-sensitive unit is demonstrated.We have conducted a comparative analysis of the different manufacturing methods of FP cavity and determined the most appropriate FP cavity manufacturing method.Through a large number of experiments,a method for optimizing the reflectance spectrum of FP interferometer is proposed.In terms of the harsh environment in oil wells,high-temperature optical fibers,steel pipes,flanges,and corrugated tubes are used as packaging materials to protect the fiber from external forces.Third,a temperature and pressure dual parameter demodulation method is proposed for the special spectrum of the temperature and pressure sensor,enables real-time,fast demodulation of sensor signals.Through long-term stability tests,it is proved that this demodulation method has good demodulation accuracy and can meet the demodulation work in this paper.At last,we conduct a series of high temperature and pressure tests on the temperature and pressure sensors.The stability,repeatability and hysteresis of the temperature/pressure detection were studied,and the total precision of the temperature and pressure sensors was studied.In the detection temperature range of room temperature to 300 °C,the applied pressure of 0 to 3Mpa showed better detection performance.The integrated temperature measurement and pressure measurement accuracy is within ±1°C and ±0.03 Mpa,and the stability and repeatability are good without significant delay.It is potential to be applied to downhole field temperature and pressure measurements.The main innovation of this paper lies in the simultaneous sensing of temperature and pressure with fiber Bragg gratings and fiber-optic FPI,which solves the cross-sensitivity problems of temperature and pressure and achieves the purpose of accurate measurement and real-time testing.At the same time,simultaneous demodulation of spectral software is developed for the signal characteristics of the temperature and pressure sensors,enabling real-time and fast signal demodulation.The manufacturing process of various FP chambers was explored,and comparisons were made with respect to reliability,repeatability,signal stability,etc.,and the best choice among the three production methods was to determine the technical selection of the pressure sensing unit.After selecting the manufacturing method,a method for optimizing the performance of the FP sensor is proposed to improve the signal quality of the sensor.Finally,system data analysis is performed on the temperature pressure sensor to evaluate the performance of the sensor.This article successfully completed the production of temperature and pressure sensors and the signal demodulation system,it will have good application prospects in Oil wells application scenarios.