Development Of Three-component Seismic Telemetry System In Well Based On OFDM

As the development of oil and gas fields progresses,the natural diminution of oil and gas reserves in China and the difficulty of development gradually increase,so more accurate monitoring means are needed to complete the fine description of reservoirs and the development of remaining oil.In-well seismic exploration technology was created in this context.Compared with the traditional surface seismic exploration technology,the seismic signal acquired in the well has the advantages of a high signal-to-noise ratio,high resolution of effective waves,and long exploration distance.Therefore,it is crucial to develop the in-well seismic telemetry system to accurately collect and record the seismic wave information in the well,and complete the data recovery with stable and accurate transmission to provide data guarantee for the subsequent seismic data processing and geological analysis,so as to play the advantages of in-well seismic exploration technology.In this paper,the overall design of the telemetry system is proposed for the seismic signal acquisition and transmission problem in the well.The data acquisition end and the data transmission end of the system are studied in depth.For the acquisition side,a low-noise and high-precision microseismic signal acquisition system is designed and implemented.For the data transmission side,a high-speed cable data transmission system is designed and implemented based on OFDM technology.And the effectiveness of the system design is verified by practical testing and system simulation.The main research contents of the paper are as follows.(1)Aiming at the low rate problem caused by the limited bandwidth of cable transmission,this paper combines Orthogonal Frequency Division Multiplexing(OFDM)with the characteristics of the cable to design a high-speed data transmission system.The transmitting and receiving parts of the transmission system are realized by FPGA hardware.The transmitter includes a scrambler,a convolutional encoder,a data interleaver,a 16QAM modulator,an IFFT module,a CP insertion module and a training sequence addition module.The receiver includes a data synchronization module,a CP removal module,an FFT module,a deinterleaver,a demodulator,a Viterbi decoder and a descrambler.The data transmission system is verified by RTL level simulation through the Vivado platform.The transmitter and receiver can send and receive data accurately.The communication rate can reach 1.2Mbps,and the bit error rate can reach the order of magnitude of 10^-7.It has excellent transmission performance indicators.Compared with the OFDM communication system designed by FPGA,the coding chip of this paper has lower power consumption,can realize real-time update and modification of hardware algorithm,and has better real-time processing capability and flexibility.(2)Design a low-noise,low-power high-precision borehole seismic signal acquisition system.The work first adopts the principle of minimum noise and impedance matching technology to design the analog signal preprocessing circuit to enhance the signal-to-noise ratio of the signal.And in-depth comparison and analysis of the current mainstream delta-sigma A/D converters,considering the actual needs and application environment,complete the chip selection and design the ADC sampling circuit.Considering that the ADC circuit will be affected by temperature,manufacturing process and device aging,causing problems such as zero drift and gain deviation,a DAC circuit is designed to provide calibration and test signals,and the circuit also realizes harmonic distortion self-test and detector impedance.Self-check function.The acquisition system has been tested by technical indicators,and the short-circuit noise level is 0.89?V at a sampling rate of 500Hz,and the dynamic range reaches 129d B,which proves that the system has low-noise and high-precision acquisition performance.In summary,the telemetry system developed in this paper has completed the design indicators and has good acquisition and transmission performance,which can provide a reference for further promoting the development of seismic exploration instruments in wells.