Research On Several Key Technologies Of Geophysical Data Acquisition System

Oil is an important resource in modern society development and oil security is related to national security. In recent years, China’s demand for oil grows rapidly. But most of the oil supply relys on foreign imports which makes it important to make more efforts on oil and gas exploration.With the advantages of high accurate, high resolution and big exploration depth, seismic exploration is the most widely used exploration technology for oil and gas. But as the exploration targes become smaller and deeper, it requires higher resolution for seismic exploration equipment. One of the most efficient way is increasing the number of sample channel in the exploration area which means increasing the density of sample channel. This requires exploration equipment data acquisition system has a large channel capacity, and in order to facilitate the construction, the data Acquisition system of exploration equipment is becoming large-channel, low power consumption and lighter.Based on the topology and function of foreign advanced data acquisition system of land seismic equipment, this thesis focuses on the following three key technologies for large-scale data acquisition system.Firstly, we designed a scalable, large-channel exploration equipment data acqui-sition system according to distributed management. The system divides massive Data Collection Unit to small zones. Each zone is managed by a Battery Management Unit which has the abilities of management, timing, power supply and data storage. Battery Management Units are also divided into several zones and managed by a Line Manage-ment Unit. The central control unit only manages the Line Management Unit and thus is freed from the management of massive units. When expanding the number of channels, data acquisition systems will increase Battery Management Units and Line Manage-ment Units. It has little effect to the central control unit and makes it be able to manage more uinits.The distributed data acquisition system also has multiple data centers, they help the central control unit for storing data, sharing its data storage pressure. When line failure comes, the management station can detect the position of failure, and reported to the central control unit; on the other hand, management uints also have a certain stor-age capacity and can scratch the sample data to ensure data security. In summary, this distributed architecture makes it possible to achieve a large channels data acquisition system and enhancing the reliability of the system. In this paper, based on the principle of LVDS transceiver, we designed a transceiver using low voltage discrete comcompo-nents. It can adjust adjusts the drive current automatically ccording to the transmission situation. In the test, after the automatic adjustment, a pair transceiver consumes less than 2 mW at 50m transmission distance and 4.096Mbps transmission rate.Secondly, some research is done for data transmission used in geophysical explo-ration equipment data acquisition system and a low power data transceiver is designed. The distance between the Data Acquisition Units is a few meters to tens of meters and data speed is 4.096Mbps. Commonly used RS485 and LVDS transceivers are able to meet the demand, but their power consumption is large which can reach tens of milli watts for a pair of transceivers. The power consumption is most concerned when de-signing and implementing the units of data collection system. We simulated the power consumption of data acquisition unit at first and highlighted the importance of reduc-ing power consumption for the power supply of data collection system. We designed an adaptive low-power data Transceiver and clock synchronization method with one-way sync frame when implementating the data acquisition unit. After the testing, the result shows that the synchronization accuracy of data acquisition unit is less than 2 mi-crosecond which meets the requirement of seismic exploration equipment. The power consumption of data acquisition unit is only 65mW which is less than the similar unit of foreign advanced data collection system.Thirdly is ablout the clock synchronization on Data Acquisition Units. Clock syn-chronization is important for the data acquisition system, including a clock frequency synchronization and time synchronization. In this design, clock synchronization per-formed in two stages. Battery Management Unit uses GPS sec pulse and UTC time for clock synchronization, and synchronization frames are generated. The synchronization frames are one-way frame and transmitted to Data Acquisition Units. Data Acquisi-tion Units recovers pulse signal from the synchronization frame for clock frequency synchronization and adjust local time to UTC time by information in synchronization frames and transmission delay between Data Acquisition Units and the Battery Man-agement Unit. This way, clock stability on Data Acquisition Units can reach 0.07ppm which is the same level of GPS clock’s. Time synchronization accuracy is less than 2 microsecond and meets the needs of the data acquisition system.The power consumption is optimized when designing and implementing the units of data acquisition system. This thesis analysis the power supply structure and the sim-ulation results. It highlights the importance of power consumption in Data Acquisi-tion Units for data acquisition system. In implementing the Data Acquisition Units, transceivers and clock synchronization methods and mainly considered, and an adap-tive low-power transceivers and one-way sync frame clock synchronous method is de-signed. Thus the power consumption is as lower as 77 mW which is less than the similar units of foreign advanced data acquisition system.The thesis is divided into five chapters:The first chapter is an introduction. It describes the demand for large-scale geo-physical exploration equipment when new exploration method requires higher explo-ration resolution. The increasing number of acquisition channel also has influence on the construction out side. So we think that the data collection system should achieve low power consumption when increase the number of acquisition channel to improve the system reliability and ensure the data safe.The second chapter analysises the existing advanced large-scale geophysical ex-ploration equipment and discusses the abilities for large-scale data collection system. Then we analysised the power supply structure of data acquisition unit chain and sim-ulated the power consumption, highlighted the importance of reducing data acquisition unit power consumption.The third chapter describes the structure of large-scale data collection system. It analysis the functions and hardware implementation of all units and improves the ex-isting technology used. It discusses the technology used in low-power data acquisition unit, mainly including the clock synchronization and adaptive low-power Transceiver.The fourth chapter tests the low-power data acquisition unit, including synchro-nization performance, adaptive low-power data Transceiver and power consumption. The test result is analysed.The fifth chapter is the summary and outlook of the thesis. It summaries the imple-mented function and tested performance and makes recommendation to further improve and tests.