Research On Downhole Multi-sensor Monitoring System Based On Analog Current Loop

The multi-sensor downhole tool is the important corollary equipment of the electrical submersible pump (ESP). It supplies the power and communicates by means of the ESP cable. By using the multi-integrated sensor and the analog current loop technique, it can detect the downhole work condition and transmit the parameters. It can offer a number of detailed parameters of downhole environment, which can be used by the operator to monitor the ESP running state and oil well production, so raising the working reliability and utilizing efficiency of ESP. It is the streamlined method used in the down-hole monitoring of the world.Six parameters such as pump intake pressure, discharge pressure, intake temperature, motor temperature, pump vibration and leakage current are monitored by the downhole monitoring system. The whole system is mainly divided into two parts: the downhole data acquisition system and the uphole data processing system. The power cable is used to carry the control and communication signals from the downhole data acquisition system to the uphole data processing system, so we need no other cables. Considering the condition of high temperature, high pressure and long distance data transmission in the oil well, an ingenious data transmission method which is based on the analog current loop was presented in this paper. Finally, the experiments show that this method is much simpler but more effective and reliable.Downhole data acquisition system is the key point of the system. It is composed of two parts, one is the parameter detecting and signal conditioning circuit, the other is the data transmission circuit. Taking into account the downhole tool structure, they were distributed in two separate circuit boards. In the data acquisition circuit, parameters were measured with high precision sensor and the signals were conditioned, while in the data transmission circuit, the voltage signals were converted to current signals and transmitted to the uphole system through the current loop. Considering the work condition and property of the system, time-sharing method was used to measure the downhole parameters. The results showed that the performance of the downhole data acquisition system met the requirements.Uphole data processing system is also composed of two parts: the data processing circuit and the downhole power supply circuit. Because of the multiple peripheral interfaces and complicated functions, ARM7 and ARM9 were used as the processors together, they communicated with each other by UART. The ARM7 system was responsible for data processing, storage and transmission, while in the ARM9 system, it accomplished parameter display and system settings. And the uphole system supplied the downhole system through a three-phase artificial reactance.After the hardware and software system were designed in detail, further experiments were done to test the system performance. The results show that the system has been basically in line with the application requirements. And the research on downhole multi-sensor monitoring system is of certain significance to the oil field exploitation.