Research On Hot-Wire Fiber Optic Sensing Technology For Low Startup Flow

In the field of oil production logging,it is of great significance to obtain the fluid flow information for the evaluation of oil well condition,the improvement of oil well recovery and the safety monitoring.With the development of petrochemical industry and the expansion of human demand for energy,production logging has been transformed from conventional logging to low permeability logging,high water-cut logging,shale gas logging and other difficult-to-tap logging.The old traffic detection methods became unsatisfactory to humans.Fiber optic sensing technology has been widely concerned by researchers in related fields because of its advantages such as high sensitivity,anti-electromagnetic interference,high temperature and high pressure resistance,small size and easy reuse.In this paper,two kinds of hot-wire fiber sensors based on the fiber Bragg grating sensor and Fabry-Perot interferometric fiber Bragg grating sensor are proposed.With the high sensitivity of hot-wire sensor to low start-up flow rate,the sensor realizes the high sensitivity,the low start-up and the fast response measurement of the flow rate.The main contents of this paper include:(1)The basic principle of thermal flow detection technology is explained including heat balance theory and heat transfer theory.The relationship between the heat diffusion rate and the fluid flow rate in the fluid domain is analyzed and calculated.A physical model of constant power heat source temperature changing with flow velocity in fluid is established by using finite element analysis.(2)A hot-wire flowmeter based on fiber grating wavelength demodulation is proposed to achieve high sensitivity,high resolution and low start measurement for fluid flow.In addition,the sensor sensitization technology and temperature compensation technology are studied to improve the sensor sensitivity and solve the problem of cross sensitivity between ambient temperature and heat source.(3)A Fabry-Perot interferometric fiber Bragg grating is proposed.An optical fiber flow sensor based on Fabry-Perot interferometry and fiber grating cascaded interferometry is fabricated to realize high sensitivity,high resolution and low start measurement of the flow.The optical fiber flow sensor proposed in this paper is based on the optical fiber thermal flow sensor.It is used to solve the problem of production logging flow detection when the flow range is 5-100m~3/d,the test temperature range is less than 200?,and the start-up flow rate is less than 5 m~3/d.