井下分布式光纤井筒温度校正技术研究与试验

油气藏的井下温度分布式动态监测技术作为油气藏开发效果评价的一项关键技术，目前主要采用分布式光纤温度传感器与井下电缆构建光电复合缆的形式来实现，然而电缆工作时产生的大量热量以及复合缆在封隔器位置的特殊结构，导致电缆产生的热量在封隔器部分出现非均匀分布， 使得分布式温度测量参数的常规校准方法难度大。 针对上述问题，文章提出了一种基于Comsol有限元局部温度场仿真与卡尔曼滤波的井下分布式光纤井筒温度校正方法。首先分析了分布式光纤工作原理，并建立了封隔器处整体式复合缆穿越三维结构， 同时构建了基于井下流体对流散热的电潜泵与电缆发热模型；然后针对井下封隔器内的复合缆穿越器，建立了基于Comsol有限元仿真软件的穿越器部分三维温度场模型，并且结合分布式光纤实测数据， 建立了井下分布式光纤温度分布状态空间方程，利用扩展卡尔曼滤波算法，实现了井下分布式光纤井筒温度的精确校准。 最后，利用所研发的温度分布式监测系统在南海某油田进行现场验证，结果表明采用三维温度场建模与卡尔曼滤波校正的井筒测量温度曲线，减轻了电潜泵电缆与封隔器对井筒温度的干扰影响，提高了井筒温度测量的精度，测量相对误差仅为0. 16%，满足生产现场的精度要求。

Research and Test of Wellbore Temperature Correction Technology with Downhole Distributed Optical Fiber

The distributed dynamic monitoring technology of downhole temperature of oil and gas reservoir is a key technology to evaluate the development effect of oil and gas reservoirs. At present, the distributed optical fiber temperature sensor and downhole cable are mainly used to construct the photoelectric composite cable. However, due to the large amount of heat generated during cable operation and the special structure of the composite cable at the packer, the heat generated by the cable is unevenly distributed in the packer resulting in the difficulty calibration of the distributed temperature measurement parameters by conventional methods. To solve the above problems, this paper proposes a downhole distributed optical fiber wellbore temperature correction method based on Comsol finite element local temperature field simulation and Kalman filtering. Firstly, the working principle of distributed optical fiber is analyzed, and the three-dimensional structure of integral composite cable crossing at the packer is established. At the same time, the heating model of electric submersible pump and cable based on downhole fluid convection and heat dissipation is constructed. Then, for the composite cable penetrator in the downhole packer, the three - dimensional temperature field model of the penetrator is established based on the Comsol finite element simulation software. Combined with the actual measured data of distributed optical fiber, the state space equation of downhole distributed optical fiber temperature distribution is established. Using the extended Kalman filter algorithm, the downhole distributed optical fiber wellbore temperature is accurately calibrated. Finally, the temperature distributed monitoring system was verified in an oilfield in the South China Sea. The results show that the wellbore temperature curve measured by 3 D temperature field modeling and Kalman filter correction can reduce the interference of electric submersible pump cable and packer on wellbore temperature. The accuracy of wellbore temperature measurement is improved with relative measurement error of only 0. 16% , meeting the accuracy requirements of production site.