Study Of Real-time Monitoring Technique For Working Fluid Level Of Production Well Based On Fibre Sensing

Oil is a national strategic resource. In the oil exploitation, production wellworking fluid level is an important fundamental date of well management. Workingfluid level reflects bottom hole flowing pressure, height of liquid column,submergence depth of well. Height of working fluid level, length and properties offoam section have a very important guiding significance in the oil extraction. Butthe current monitoring technique for working fluid level have significant deficiency.For wells without foam section, monitoring accuracy is low, and unable to achievereal-time on-line monitoring. For wells with foam section, unable to accuratelymonitor the position of working fluid level, and unable to know properties of thefoam segments.This article is based on the theory of optical fiber sensing, on the basis ofoptical properties, such as, electromagnetic interference resistance, corrosionresistance, safety, long-distance monitoring, enabling distributed sensing, etc,presents monitoring programs for no foam segment wells and wells containing foamsection. Combination of two solutions is able to achieve the real-time on-linemonitoring of the position of working fluid level, the length, density and gascontent of foam segment.This article designs a flat diaphragm-equal strength beam sensor to monitor theworking fluid level of wells without foam segment. Establishing the relationbetween height of working fluid level and the centre wavelength of FBG (FiberBragg Grating, FBG for short). Designed sensor has the function of temperatureself-compensation, the performance can meet the design specifications. The staticsanalysis of sensor is made using ANSYS, mechanical properties meet therequirements and the simulation agree well with the theoretical value.For wells containing foam section, proposing a method of electric tracing bandauxiliary heating to monitor the working fluid level. Derived the relation betweenheat source heating time and temperature response of surrounding medium usingheat transfer theory. Based on principle that Raman Optical Time DomainReflectometer (ROTDR for short) only demodulated by the temperature, monitoringdifferent temperature rise in different surrounding medium can monitor the positionof working fluid level and the length of foam section. Non steady heat transferanalysis using ANSYS proved that electric tracing band auxiliary heating to monitorthe working fluid level is feasible.Combining the two programs to create distributed fiber Raman sensor systemand the quasi-distributed sensor system, derived theoretical formula of average density and gas content of foam section. Then the real-time on-line monitoring ofthe position of working fluid level, the length, density and gas content of foamsegment can be achieved. At last, the experiments are made. Designed sensor isvery small in size, its linearity is well and sensitivity is high. Gas-liquid experimentof electric tracing band auxiliary heating is made for air and water, experimentalresults and theoretical analysis, ANSYS simulation results generally in line, theerror does not affect the result of this method for monitoring of working fluid level,and the method can meet the monitoring requirements.