Research On The Measurement Method Of Downhole Pressure And Temperature Based On FBG

With the continuous improvement of the degree of oil exploitation,the demand for underground operation is constantly increasing.In the process of deep oil exploitation and underground operation,the role of pressure and temperature detection is increasingly prominent.The detection of pressure and temperature is not only helpful to understand the working status of underground pipes and tools,but also to prevent the occurrence of underground safety accidents,which plays an important role in improving the stability of underground mining system.Due to the problems of poor anti-electromagnetic interference,low safety factor,long-distance transmission signal distortion,difficult to realize distributed measurement and easy to fail in high temperature and high-pressure environment in the traditional downhole pressure and temperature detection method,to achieve the stable measurement of downhole pressure and temperature,it is necessary to propose a more safe and efficient downhole measurement method.Because FBG has the advantages of anti-electromagnetic interference,high-temperature resistance,corrosion resistance,long-distance signal transmission stability,and easy to distributed measurement,it has a broad development prospect in downhole pressure and temperature measurement.This paper mainly designs a distributed downhole pressure and temperature monitoring system based on FBG.In this system,the sensing principle of FBG is applied to the measurement of downhole pressure and temperature.Compared with other FBG sensors,the distributed monitoring of downhole pressure and temperature is realized.The main contents of this paper are as follows:By analyzing the development status of traditional downhole pressure and temperature monitoring system,it is concluded that in the process of downhole pressure and temperature measurement,the monitoring system should have the characteristics of real-time monitoring,high temperature,pressure resistance,and distributed permanent measurement.According to the sensing principle of FBG,through analyzing the sensing method of FBG for liquid pressure and temperature and the form of temperature compensation in pressure monitoring,combined with the underground environment,the pressure and temperature monitoring scheme of the sensor is preliminarily obtained.At the same time,according to the distribution model of the temperature field in the underground environment,the layout scheme of the sensor is designed.According to the proposed pressure and temperature monitoring scheme,the specific structure of downhole pressure and temperature sensor is designed.Based on the structure of the proposed sensor,the theoretical sensitivity of the sensor is analyzed.Using the finite element simulation to simulate the sensor structure,through the comparison between the theoretical model and the simulation model,the correctness of the theoretical model is verified,and the feasibility of the sensor is analyzed.Based on the designed sensor structure,an experimental platform is built.Through polymer calibration experiment and sensor pressure-temperature calibration experiment,the performance of the sensor in the actual measurement is obtained.By analyzing the error between the experimental results and the theoretical results and the causes,the feasibility of the sensor in the actual measurement is verified.The pressure sensitivity and temperature sensitivity of the sensor are-46.117pm/MPa and 11.670pm/? respectively.After temperature compensation,the pressure measurement error is less than 0.1MPa.The measurement performance of the sensor meets the actual measurement requirements,and it can realize the highefficiency measurement of downhole pressure and temperature.