Research On Detection Method Of Down-hole Parameters Based On Fiber Bragg Grating

In the process of oil exploitation,the exact detection of down-hole parameters contributes to the comprehension of down-hole tools working state and then protects the down-hole tools and prolong their service life,meanwhile,it can effectively prevent the happening of the down-hole safety accidents,what's more,it's the vital basis for rational exploitation of the underground reservoir and of great guiding significance in underground work.At present,traditional electric sensors are widely used in the down-hole pressure and temperature parameters measurement but it cannot realize the real-time monitoring permanently due to the high pressure,high temperature,complex underground environment,sensors' own security risks and poor measurement reliability.For down-hole axial force and torque measurement,resistance strain sensors are more popular,however,this method needs large numbers of resistance strain gauges,and it also requires complex processing circuit and structure.In addition,resistance strain gauge is sensitive to the environment temperature,its stability and reliability changes with the environment,so it's difficult to meet the needs of the complex underground environment.In addition,there are barely no measurement methods of down-hole temperature,pressure,axial force and torque simultaneously.Fiber Bragg grating sensor is very suitable for the application in the field of oil industry because of its essential security and strong ability to resist electromagnetic interference,the advantages of small volume,high measuring precision.Under these circumstances this paper proposes a method of down-hole multi-parameter detection based on fiber Bragg grating.Firstly,this paper summarizes the development situation of underground multi-parameter detection at home and abroad and the general situation of fiber grating sensing monitoring,puts forward a new method of down-hole multi-parameter detection based on the fiber Bragg grating sensing technology combined with complex underground environment,then,on the basis of analyzing the detection principle of fiber Bragg grating and conducts the modeling and theoretical analysis respectively for down-hole detection principle of axial force,pressure and torque.Besides,it expatiates the paste location and decouples the multi-parameters and then analyzes the down-hole multi-parameters measurement pup-joint and its specific work process in detail.Based on above work,this paper conducts the underground axial force measuring static characteristic simulation analysis,down-hole rod torque measuring static characteristic simulation analysis and down-hole pressure measuring static characteristic simulation analysis with the help of finite element analysis software ANSYS which acquire the strain and deformation distribution characteristic of measurement area strain,verify the detection theory and optimize the paste location of fiber Bragg gratings.Then,according to the pressure detection principle of fiber Bragg grating,this paper also conducts the experiment of pressure detection method based on fiber Bragg grating technology in the laboratory.According to the design of the fiber Bragg grating pressure sensor and other experimental apparatus,this paper builds a set of experiment platform of characteristics research of down-hole pressure measurement and compares the simulation analysis results with the theoretical analysis through the experiment data analysis.The results show that the optical fiber Bragg grating pressure sensor has good static characteristic,its measurement method is feasible and reliable.Finally,this paper summarizes the research results and prospects the existing problems.