Accuracy Analysis Of The Torsional Vibration Measurement Of Viscosity Based On Fiber Bragg Grating

The oil viscosity is one of the most important indexes of the oil and gasmigration, accumulation and oil gas field development. Accurate measurement ofviscosity index has important significance In the oil industry、 food industry、paintindustry、polymerization coating industry and other industry. The current commonlyused viscosity measurement method includes capillary tube method, rotation method,the falling ball method and vibration method and so on. These measurement methodshave been very mature, and widely used. However, in bad environment to implementthe on-line measurement of viscosity, still exist many problems. As the average depthof oil well up to km, in the deep, the high temperature、high pressure、strongelectromagnetic interference environment, as well as wellhead bore restriction, allaffect on viscosity sensor material, structure, technology and other aspects, so themeasuring part has the features of small size. Because of the measuring principle andtechnological limitations of the traditional viscosity instrument, they aren’t suitable forfield application. Therefore, task group proposed torsional vibration viscometersensing method based on FBG(Fiber Bragg Grating).Aiming at the problems in torsional vibration viscosity measurement thatsensitivity is influenced by different shapes of probe subjected to different viscousforce, the measuring accuracy and sensitivity of cylindrical probe, spherical probe andcone probe are studied according to the principle of viscosity measurement based onFBG micro-torsional vibration. Through the mathematical model built for differentprobes, corresponding voltage-viscosity formulas are derived, then in laboratoryenvironment, the undetermined coefficient is got from calibration experiment, and themeasuring characteristics are compared between the three probes. The experimentaldata shows that cylindrical probe is more accurate and more sensitive than sphericalprobe and cone probe, which verifying the theoretical analysis. At the same time, wealso analysis the other factors that influence the measurement accuracy, and thesolving methods are presented to provide theoretical basis for the further experiment.