Long-distance Oil And Gas Pipelines Sensing Technique Based On Brillouin Optical Time Domain Analysis

The distributed fiber sensor differs from traditional sensor, and it characterized by itssmall size, light weight, stronger anti-interference, higher sensitivity. The distributed fibersensor can be formed as two dimensional or three dimensional sensor network and it can alsotest the normal condition of the large-scale and long-distance structure. According to the timedomain analysis of Brillouin (BOTDA), the distributed optical fiber sensing technology hasmany advantages of the general fiber optic sensor and achieves the distributed detection ofhigh-precision, high spatial resolution and real-time dynamic.It introduces the present situation on BOTDA at home and abroad, and analyses themechanism stimulated Brillouin scattering mechanism, and deduces the functionalrelationships between Brillouin frequency shift, temperature and strain. After the temperatureand strain experiments, the1MHz/℃temperature sensitivity and0.031MHz/℃MHz/N strainsensitivity are obtained. For the requirements of the large-scale structure of the whole scaledistributed high precision temperature measurement, BOTDA method and FBG temperaturesensing technology are used to design a temperature sensing test system. The system iscomposed of BOTDA analyzers, FBG demodulator, collinear sensing probe and opticalswitches. The experimental test proves the system has function of testing large range ofdistributed temperature and local precision temperature. So the complementary of BOTDAtemperature measurement technology and FBG temperature sensing technology is achieved,the contradiction of measurement range and measurement precision is solved. What is more,the system has good temperature repeatability and the expected design requirements areachieved. The collinear measurement technology program has broad application prospects inthe large-scale structure of temperature monitoring. We designed a kind of strain sensing cablebased on sensitive material of crude oil by the requirement of small-scale pipeline andhigh-precision leak detection, and also the response model of the brillouin frequency shift oflocal strain on the fiber optical cable was proposed to discover and locate the leak event. In theformed simulation system, we located the small-scale oil leak accurately within15minutes bythe distributed detection of brillouin frequency shift caused by oil leak using BOTDA, besides, the spatial resolution of1m and the positioning error of o.1m in the length of1.714km wererealized.Based on the MFC class library, windows platform is utilized to develop a tool waveshowfor a warning software, which alarms when the set threshold value point is exceeded. At thesame time, the warning software can locate the fault point to achieve the prewarning.