Research On Seismic Wave Observation Method Based On Distributed Optical Fiber Acoustic Sensing Technology

Observing seismic waves is to observe the vibration signal generated by the seismic source and the propagation process of the vibration signal in the earth medium.In large-scale bridge condition monitoring,pipeline surrounding safety monitoring and other engineering applications,it is necessary to detect and analyze ground vibration signals to predict potential risks to ensure engineering safety,people's lives,and national property safety.The traditional method of seismic wave observation is to use electronic geophones to record seismic related data.This type of electronic geophone is a single-point geophone.When used,it is necessary to connect multiple electronic geophones in series and then deploy them on the surface or downhole.The engineering cost is expensive and the construction period is high.Long and difficult to construct.Distributed optical fiber acoustic sensing(DOFAS,referred to as DAS)technology,by measuring the phase change of the scattered light back to Rayleigh in the optical fiber,only one optical cable can realize the detection and monitoring of vibration events along the line It solves the problems of high cost and difficult construction of electronic geophones,and has good engineering practicability.This thesis researches the seismic wave observation method based on DAS technology.The main elements and innovations are as follows:Based on the principle of DAS technology,the research on the response of the optical fiber to the seismic wave field and the response of the optical fiber to the seismic vibration signal were carried out from different angles.Aiming at the problem of the low longitudinal vibration response of the optical cable,the optical cable sensitivity-enhancing DAS system was researched and designed.And carried on the mechanical model analysis.The performance test experiment of the DAS system shows that the DAS system maintains a good response to the vibration source frequency of 50?500Hz;the system has a spatial resolution of 13.4m at 15 km,which meets the demands of engineering applications better;the system has the largest effective sensing distance Positioning error is less than 14 m.Under the two different observation conditions of laying optical cables on the ground and laying optical cables in the underground,the most optimal layout schemes of optical cables are studied,and a new way of laying optical cables on the ground is proposed.After conducting the response comparison experiment with the geophone,the results show that The seismic wave observation method based on DAS technology is dominant in the rapid deployment of sensors and the response to vibration is consistent with the geophone.It provides solutions to the suppression of time-varying noise and random optical noise in the well in DAS-VSP logging.The application of DAS technology in pipeline safety monitoring projects has been tested for leakage and vibration.The results of the leakage test show that the DAS system can clearly see the pipeline leakage from the time-space diagram of the vibration signal under the airflow pressure of 1000 pa and 2000 pa.Information,and the main frequency of pipeline vibration caused by a leak point with a diameter of 4.5mm is below 3k Hz.In the vibration test,we proposed a scheme of pipeline vibration signal enhancement and pattern recognition to solve the problem that long-distance distributed optical fiber sensing system is difficult to effectively identify the type of vibration intrusion signal.