DAS技术在井中地震勘探的应用

分布式光纤声波传感技术(distributed acoustic sensing,DAS)是利用光纤本身作为传感器进行信号采集的一项新兴技术,在国外井中地震勘探的应用发展迅速。为了验证DAS在井中地震勘探应用的适用性,结合DAS在井中地震采集应用实例,简述了DAS技术原理及其在井中地震勘探的实施方法,对比了DAS与常规检波器、可控震源与炸药震源不同激发方式、套管内与套管外不同布设方式的采集资料;以可控震源采集资料为例分析了DAS与常规检波器采集资料直达波振幅衰减规律、不同入射角直达波振幅响应、频谱、子波波形的差异;指出了DAS与常规检波器Z分量采集资料具有较好的一致性,可以部分替代常规检波器Z分量的采集工作;通过对比套管内悬置和套管外水泥固井两种不同光纤布设方式采集资料的直达波振幅响应,认为固井光缆具有与地层更好的耦合效果,同时不易受到井筒内因素的干扰。随着DAS技术的不断进步,凭借其高密度、全井段和高效施工等优点,DAS的应用将逐步拓展到石油勘探的更多领域。

Application of distributed acoustic sensing in borehole seismic exploration

Distributed acoustic sensing(DAS)is a novel technology that uses optical fiber as a sensor for signal acquisition.It has developed rapidly in the field of borehole seismic exploration worldwide.To verify the applicability of DAS to borehole seismic exploration,data acquired by DAS and conventional geophones,under vibration and dynamite excitation,both inside and outside the borehole casing,were compared.Considering the data obtained by vibration excitation as an example,we analyzed the attenuation law of the amplitude of the direct waves,amplitude response,frequency spectrum,and wavelet shape of the direct waves at different incident angles collected by DAS and conventional geophones.The analysis indicated that the data from DAS were well consistent with the Z-component records of conventional geophones.Therefore,it can be inferred that DAS can partially replace the Z-component from conventional geophones.We also compared the amplitude response of direct waves recorded by an optical fiber cable both inside and outside the borehole casing.The results showed that the cemented cable outside the borehole casing has better coupling effect with the formation,while it was not easy to infer from the noise in the wellbore.The application of DAS will gradually expand to more areas of petroleum exploration because of its advantages in terms of high density and efficient construction in the whole well section.