Abstract: Based on the HART communication protocol, an intelligent pressure detection system for water injection wells in oilfields was developed, realizing intelligent detection of pump pressure and casing pressure in water injection wells and centralized management of pressure data, providing a reference for oilfield production decisions. The system composition and the basic principles and implementation methods of each part are introduced. Keywords: monitoring system; pressure detection; water injection well in oilfield; HART protocol; data acquisition CLC Number: TP274 Document Code: B An oilfield production area consists of multiple oil wells, water injection wells, metering rooms, manifold valve groups, oil transfer stations, combined stations, crude oil export systems, oil tanks, and other dispersed facilities in the oilfield. The working status of various facilities in the entire production area and the data of produced oil (mainly temperature, pressure, flow rate, etc.) are directly related to the stability of oilfield production and crude oil quality. After an oilfield begins production, as extraction time increases, the energy of the reservoir itself is continuously consumed, leading to a drop in reservoir pressure, significant degassing of underground crude oil, increased viscosity, and a substantial reduction in well production. This can even result in well shutdowns and the accumulation of large amounts of dead oil that cannot be extracted. To compensate for the underground deficit caused by crude oil extraction and to maintain or increase oilfield production, it is essential to maintain or increase reservoir pressure. Currently, the main method for increasing reservoir pressure is through the injection of high-pressure water into injection wells. Therefore, oilfields place great emphasis on well pressure management for injection wells. However, China lags behind in the detection of water injection well pressure data. The detection instruments and equipment are outdated, and there are many problems with the reliability of the pressure data. The currently used spiral spring tube pressure gauges are not only labor-intensive but also affect the real-time performance and reliability of equipment monitoring and oil production data. Furthermore, due to the large number and wide distribution of injection wells, and the varying skill levels of oilfield workers, data omissions and falsifications occur frequently. Therefore, researching and developing new intelligent instruments to reliably detect water injection well pressure data is extremely urgent, providing a reliable data source for oilfield production. Utilizing computer and internet technologies to research and develop an oilfield water injection well pressure detection system will play a positive role in promoting the informatization of oilfield production. The HART (Highway Addressable Remote-Transducer) protocol is a widely used communication protocol between intelligent instruments and upper-level management equipment. It adopts a simplified ISO/OSI model, namely the physical layer, data link layer, and application layer. The following describes the construction of an intelligent pressure data detection system for oilfield water injection wells based on this communication protocol to achieve remote transmission and management of water injection well pressure data. 1. Composition and Principle of the Water Injection Well Pressure Detection System The oilfield water injection well pressure detection system mainly consists of a new type of intelligent pressure sensor, transmitter, handheld instrument, network communication line, and microcomputer database management system. Each water injection well is equipped with a transmitter unit, which is interconnected with the main unit of the sub-detection station through a HART communication interface. The sub-detection station is mainly responsible for collecting pressure data, connecting to the transmitter's HART communication module through an RS232 interface to collect pressure data from each water injection well. The sub-stations collect and aggregate the data, then upload it to the central station host via the oilfield local area network for centralized data management. The overall system block diagram is shown in Figure 1. 1.1 Intelligent Pressure Sensor The intelligent pressure sensor consists of a diffused silicon pressure sensor and its encoding circuit. When water pressure from the injection well pipeline acts on the sensor diaphragm, the diaphragm deforms, causing a change in the resistance of the corresponding sensor bridge arm. This change generates a small differential voltage signal at the output terminal via a constant current source. The voltage signal is then amplified using high-precision, low-drift amplification devices, and the input differential voltage signal is conditioned into a 4-20mA current output via a V/I module. To distinguish the data from different injection wells, the sensor itself must be encoded. The sensor encoding uses an RC oscillation circuit to output a square wave signal of a certain frequency after shaping. The frequency is adjusted by a resistor, and this frequency signal is superimposed on a 4-20mA analog signal. The sensor block diagram is shown in Figure 2. In practical applications, the bandwidth of the sensor output frequency is limited by the transmitter system's operating frequency. The lower the system operating frequency, the lower the required sensor output frequency and the narrower the bandwidth. Since the sensor output frequency is composed of an RC oscillation circuit, the oscillation frequency fluctuates due to the influence of the ambient temperature. A higher oscillation frequency occupies a wider bandwidth, allowing the system to identify more sensor numbers. Let the transmitter unit crystal oscillator frequency be f[sub]cx[/sub], then the system's highest counting frequency is f[sub]co[/sub]. Assuming the encoding frequency is allowed to fluctuate by 5%, and that the frequency segments do not overlap, then the center frequencies of each segment, f[sub]i[/sub] (i=1, 2, ...), satisfy 0. 2 Conclusion The intelligent pressure sensor, detector and data management system of the water injection well pressure detection system has been tested in Daqing Oilfield since December 2002 and has been running successfully for more than a year. The data collected on site shows that the output accuracy of the pressure sensor is less than 1.5% under the low temperature in winter and high temperature in summer, which is much higher than the accuracy of the spiral spring tube pressure gauge. In terms of the arrangement of intelligent sensors, the installation and sealing problems have been solved well. The test results show that the intelligent detection system of water injection well pressure data is stable and the pressure data is true and reliable. As an important part of the oilfield informatization construction, the research, development and application of the oilfield water injection well pressure data management system will play a positive role in promoting the informatization construction of the oilfield. References: [1] Shangguan Yongliang, Zhao Qingdong, Song Jie, An Zhen. Research on rational water injection method of water injection well. Daqing Petroleum Geology and Development, 2003, (3): 40-43. [2] Sun Guangjun. HART field communication protocol. Electric Power Information, 2002, (3): 66-68. [3] Zhang Shilun. HART Communication Protocol and Applications. Automation and Instrumentation, 1999, (5): 3-6. [4] Cobb Jim. Control in the Field With HART Communications III. ISA Transactions, 1996, 35: 165-168. [5] Helson Ronald B. The HART0 Protocol and Enabler for Improved Plant Performance. ISA Transactions, 1996, 35: 159-164. [6] Chen Dongyu, Shi Yiming, Jin Jianxiang. Intelligent Diffused Silicon Pressure Transmitter Based on HART Protocol. Automation Instrumentation, 2001, (6): 17-19. Please click to download the original text: Research on Pressure Detection System of Water Injection Well Based on HART Protocol.pdf