DAS-VSP采集处理方法研究及应用

分布式光纤声波传感技术(DAS)是通过解调光信号背向瑞利散射相位变化表征地震信号的一种新型信号采集技术,其在井中采集具有一次性覆盖全井段和测量高密度的特点,施工效率和数据的一致性大幅提高,因此受到广泛关注。以光纤在井中地震的实际应用为例,讨论了影响DAS采集资料信噪比和分辨率的光信号解调因素和采集因素,提出了一种在无检波器定位情况下校正DAS深度位置的解决思路,利用时间方向求导和反演耦合干扰减去法提高了DAS-VSP采集资料的上行波信噪比和全波场高频成分。基于预处理后的高密度DAS-VSP数据,提取了层速度、各向异性参数用于深度域井控各向异性偏移,通过井控各向异性叠前深度偏移,使偏移成像频带拓宽约20Hz,主要目的层井震误差小于0.15%,展现了高密度DAS数据在井中地震中良好的应用前景。

Research and application of the DAS-VSP acquisition and processing method

Distributed optical-fiber acoustic sensing(DAS)is a new type of acquisition technology that uses backward Rayleigh scattering to demodulate the phase change of optical signals to characterize seismic signals.DAS is characterized by logging-scale density;as such,a single VSP acquisition can cover the entire distance from the surface wellhead to the end of the deployed fiber in the well.Because of its advantages,DAS has received widespread attention,leading to great improvements in construction efficiency and data consistency.In this work,a case in which DAS was applied for borehole acquisition is presented.The optical signal demodulation and acquisition factors that affect the SNR and resolution of the DAS data are discussed,and a method to calibrate DAS-VSP data without simultaneous geophone acquisition is developed.The SNR of the upward wave and the high frequency part of the full wave field can be improved by subtracting the inverse DAS coupling noises and estimating the time derivative.From the pre-processed high-density DAS-VSP data,the layer velocity and anisotropy parameters are extracted and used for well-controlled pre-stack anisotropic depth migration,which has broadened the frequency band by approximately 20Hz,and resulted in a borehole seismic error of the main target layer of less than 0.15%.These results show that high density DAS has good application prospects in borehole seismic studies.