Research On Downhole Acoustic Communication System

Digital oil field is the trend of oil exploration and development in the future.Over the past decade,intelligent completion technique has been quite perfect abroad,while little research has been done in China.At present,data transmission based on cable or optical fiber is widely used for mature intelligent completion systems.Logging cables will interfere normal oil extraction.Wireless transmission,by contrast,has less impact on oil production.Among the commonly used wireless transmission,acoustic communication has the advantage of small amplitude attenuation and no special requirement for transmission media so that it is suitable for downhole data transmission.To realize the whole communication system,the difficulty lies in the fact that the amplitude and phase of the signal are distorted when the acoustic wave is transmitted in oil tube,which makes it difficult to extract the synchronization signal and demodulate the received signal.Aimed at the problems above,this paper analyzed the theoretical model of downhole acoustic communication system and fundamentals of common digital modulation.Based on these,the general structure of 2FSK modulation communication system is proposed.According to the overall design,related works have been carried out.Direct digital frequency synthesis technique allows the transmitter to generate desired carrier signal easily.To simplify the hardware circuit and improve the system integration,a demodulation scheme based on software platform has been proposed.Digital receiver are used so that software demodulation can be realized.Dealing with the possible amplitude and phase distortion of received signal,three-envelope-laying demodulation has been put forward on the basis of 2FSK zero-crossing detection.The synchronization signal is extracted according to the idea of grouping and step-by-step detection.The code group is identified from sample points,and then the synchronization information is extracted from code group.According to the above design,the sending and receiving circuits and demodulation program are developed.Both the modulator and the demodulator of this system can be programed.With less circuit,the adjustment of sending and receiving parameter is convenient,which makes the system more potable.Synchronization and demodulation method has a certain anti-interference capability.The system can communicate as expected and has the advantage of simple,reliable and easy to implement.Above all,the difficulty has been researched that acquiring logging data by acoustic waves in intelligent completion system.The experiment indicates that the communication system is reliable when the transmission rate is lower than 2 kbit/s,and this scheme has reference value for the research of downhole acoustic communication.