基于分布式光纤传感技术的海底高压天然气管道泄漏检测方法

For security of sea energy supply, subsea pipelines are being laid over longer distances in seafloor areas affected by geohazards, harsh environmental conditions. Deep water high pressure gas flowlines have introduced new challenges in terms of pipeline leakage and integrity management as the assets are submitted to seabed erosion, imgrating bedforms. Based on hybrid Sagnac and Mach-Zehnder interferometer, a novel distributed fiber optic sensro structure was proposed. The project main content includes.(1)Based on distributed fiber-optic sensor structure based on the principle of Sagnac and Mach-Zehnder mixed distributed fiber-optic interferometer, the system is able to monitor 50 kilometer inspection span of gas pipeline. The single point and multi-leakage points location algorithm was proposed.(2) Sea floor noise (the mixture of Gaussian noise and non-Gaussian noise) model was studied. Under a unified framework, non-Gaussian statistical model was selected as the model, then non-linear statistal signal filter algorithms (polynomial filter and Median/Myriad filter) based the proposed model are used to process sea floor noise.(3)The digital phase generated carrier demodulation hardware for large dynamic and high sensitivity of signal demodulation was developed. Based on simulation and sea trial data analysis, the hardware performance was evaluated. We hope to gain optimum demodulated broad frequency band gas leakage signal and improve demodulation signal-to-noise ratio(SNR).The dynamic range of digital PGC demodulation scheme will be extended, compared with analog electronics.(4)The temperautre calibration model and optical polarization model based on the equivalent Jones matrix of the single-mode optical fiber birefringence were built. The gas leakage caused leakage point surrounding water temperature variation, which produced interferometric signal phase drift. Polarization- induced fading cotrol scheme was presented.(5)The high pressure gas releasing from the leakage points will scour the seabed. The gas bubbles mixed with muddy water.The bubble acoustic source in this special circumstance owns unique feature. The acoustic charactristics of leakage source are required to be analyzed in detail(frequency features, propagation path). The relation between gas leakage source and null-frequency localization disturbance was described. The gas pipeline leakage detection performace of distributed fiber-optic sensor was evaluated in lake and sea, when testing space is 50 kilometer. This technique supplies the solid foundation for underwater high-pressure gas pipeline safety operation.

为保障海洋能源供应安全，围绕海底高压天然气管道泄漏实时检测问题，基于Sagnac和Mach-Zehnder全混合干涉型分布式光纤技术，拟研究内容：（1）研究单、多泄漏源检测与定位方法，实现50 km有效测试间距的海底高压天然气管道泄漏实时监测；（2）研究海底环境噪声(高斯/非高斯并存)的非高斯随机过程建模，提出适应模型的非线性统计信号滤波与处理方法(多项式滤波和Median/Myriad滤波系统)，结合仿真和水下测试数据，归纳噪声建模的理论框架；（3）研究干涉信号的相位产生载波(PGC)全数字化解调技术，实现宽带PGC解调获得最佳相位干涉信号；（4）建立温度标定模型，分析泄漏点周围温度变化对干涉光相位的影响，结合琼斯矩阵模型控制干涉光偏振；（5）研究分布式光纤检测系统在海底混浊水区域检测性能，结合湖试和海试数据揭示泄漏源与零点频谱间耦合关系，为海底天然气管道安全运行提供技术支撑.

本课题研究了Mach-Zehnder和Sagnac的混合干涉原理，针对水下管道应用环境，开发了用于水下高压天然气管道泄漏检测和定位的分布式光纤传感系统。主要内容包括：(1)在原有泄漏检测装置的基础上，开发了基于MCU的干涉型光纤传感器全数字化PGC解调硬件装置，提高信号的解调性能；(2)对于所开发的干涉型光纤传感器管道泄漏检测装置的定位性能进行了性能分析（测试间距10km时，系统的灵敏度约0.5 Hz/m），总结了分布式光纤检测系统的定位精度、稳定性、灵敏度等；（3）提出基于支持向量机的分布式光纤泄漏检测定位方法，利用多组泄漏点样本，依据支持向量机建立样本数据的回归模型，对支持向量机的相关调整参数进行了优化，提高了泄漏点定位精度；（4）针对该系统光路架构中存在的偏振信号衰落，建立了基于琼斯矩阵分析的的传输光数学模型，分析和研究检测系统在有泄漏、无泄漏以及不同泄漏点位置处对输出干涉光谱的影响；（5）针对水下天然气管道泄漏检测系统中出现的误报（虚报和漏报）现象，选取 40mm钢质管道和带防腐层100 mm的钢质管道作为研究对象，统计了分布式光纤检测系统虚警率和漏警率。采用基于小波包能量特征提取和基于欧式距离法的聚类分析对泄漏信号进行处理，对管道泄漏进行预警和精确定位。