基于DFB-FL的井下小流量实时监测关键技术的研究

The key real-time monitoring technology of downhole small flow can provide a scientific basis for optimizing oil and gas exploration programs and enhanced oil recovery.A highly sensitive optical fiber distributed feedback laser (DFB-FL) is used as a sensing element for downhole environment and the weak flow signal, and the key real-time monitoring technology of downhole small flow is proposed. By analyzing the sensing mechanism of DFB-FL on small flow sensor, the theoretical relationship model between DFB-FL wavelength and the average velocity of the turbulent is established; and we identify how the production parameters of phase- shift grating such as phase shift amount, phase shift location and lasing window influence on power and line-width of the DFB-FL, and we produce the downhole small flow sensor; we propose the improved program of 3 × 3 coupler demodulation scheme by eliminating the angle influence and unbalance Michelson interferometer with Faraday rotation mirrors to eliminate polarization effect; Temperature compensated, the substrate sensitizer and spatial filtering methods are applied to eliminate the influence of environmental factors on downhole small flow monitoring base on DFB-FL. The downhole small flow measurement method based on DFB-FL is created to solve the problem of real-time monitoring of downhole flow from theory and experiment.

井下小流量实时监测为优化油气开采方案及提高原油采收率提供科学依据。针对井下环境及小流量信号微弱特性，本项目采用具有高灵敏度的分布反馈光纤激光器（DFB-FL）作为传感元件，进行井下小流量测试关键技术的研究。通过分析DFB-FL小流量传感器的传感机理，建立DFB-FL波长变化与湍流平均流速关系理论模型；找出相移光栅的相移量、相移位置以及激射窗口等制作参数对DFB-FL出光功率及线宽的影响机理，制作适用于井下小流量的DFB-FL；提出消除3×3耦合器夹角影响的改进解调方案和消除偏振影响的带有法拉第旋转镜的迈克尔逊非平衡干涉仪光路优化设计；采用温度补偿、基材增敏、空间滤波等方法消除井下环境因素对DFB-FL小流量监测的影响。从理论和实验上创建一种基于DFB-FL的井下小流量监测关键技术，解决井下小流量实时监测的难题。

井下小流量实时监测为优化油气开采方案及提高原油采收率提供科学依据。针对井下环境及小流量信号微弱特性，本项目采用具有高灵敏度的分布反馈光纤激光器（DFB-FL）作为传感元件，进行井下小流量测试关键技术的研究。通过分析DFB-FL小流量传感器的传感机理，建立DFB-FL波长变化与湍流平均流速关系理论模型；找出相移光栅的相移量、相移位置以及激射窗口等制作参数对DFB-FL出光功率及线宽的影响机理，制作适用于井下小流量的DFB-FL；提出消除3×3耦合器夹角影响的改进解调方案和消除偏振影响的带有法拉第旋转镜的迈克尔逊非平衡干涉仪光路优化设计..项目设计的传感器在10Hz~500Hz的范围内频响相对平坦，并且具有较高的线性度。 在实验中，采用能量分析方法实现了0.6 m3 / h~25.5 m3 / h的流量范围、 最小流量为0.046 m / s的测量。 实验结果证明了基于DFB-FL的新型非浸入式流量测量方法的可行性，并实现了小流量的精确测量。