Development Of Casing Valve For Pressure Detection Based On Optical Fiber Sensing Technology Research

The status of development of international downhole casing valve bottom pressuretesting is reviewed.,and the existing pressure testing equipment, the advantages anddisadvantages of electronic pressure sensor and mechanical pressure sensor isresearched. Combining with the special environment and the characteristics of thedetection of downhole pressure, the scheme based on optical fiber acousto-opticmodulation valve pressure detection is proposed. The system combines with theoptical fiber sensing technology, photoelectric conversion technology, signalprocessing circuit and PC display technology based on Labview. The measurementsystem can meet the following conditions: downhole temperature125℃, measuring alength of1500m, pressure measurement range from10to35MPa.The sensitive element is elastic tube. the measurement fiber winding on the elastictube, the light modulation is based on the principle of the phase modulation. Thestructure of the measuring system is designed, including test nipple, measuringoptical fiber, optical fiber and the photoelectric conversion, signal processing anddisplay interface. In view of the element, analysis of the stress change caused by thefiber structure changes, thus caused changes in the light, then the photoelectricconversion and circuit processing caused by voltage change, finally established themathematical model, determine the corresponding relation of the voltage and phase,the downhole pressure value is obtained. In order to eliminate the influence oftemperature, selected the DTS optical fiber temperature sensor.In view of the special environment of the underground, the hardware ofmeasurement system is designed, choose STC12C5410AD series MCU realizehigh-speed data acquisition and A/D conversion. ZY_WHAD-3w series powermodule supply for the whole circuit. The design of the optical system including theselection of light source, the selection of acousto-optic modulator, and the selection ofthe photoelectric detector. The display system is the display module which is basedon Labview. Software design includes collection procedures and A/D conversionprogram, the design of the rear panel display system and the temperature and othercompensation program.In the end, designed the optical fiber sensing system of the downhole casing valve,and has carried on the test of the system. Preliminary completed laboratory data acquisition and analysis. At the same time, analyzed the sources of uncertainty.Calculated the relative uncertainty and expanding uncertainty of the measurementresults. The synthetic measurement uncertainty was0.2381%. The expandeduncertainty was0.4762%. The design will provide a new method for the pressuremeasurement of the measurement system when oil well casing valve closing or fordownhole pressure measurement in the future.