Deformation-rate distributed acoustic sensing: filtering and coupling considerations

Deformation-rate distributed acoustic sensing (DAS), made available by the unique designs of some interrogator units, can acquire seismic data that are equivalent to the along-fiber particle velocity motion recorded by geophones for scenarios involving (near-)elastic ground-fiber coupling. While near-elastic coupling is straightforward to achieve in cemented downhole installations, it is less clear how to do so in lower-cost horizontal fiber deployments. This investigation illustrates that near-elastic coupling can be achieved by installing and freezing in fiber in shallow backfilled trenches. Any existing residual unwanted signals can then be removed through 1D or our preferred 2D dip-velocity filtering approaches. The processed deformation-rate field records acquired at the surface and two different trenching depths show clear surface- and refracted-wave arrivals; however, the surface-deployed fiber records exhibit significant time-lapse amplitude variations corresponding variable gro...

借助部分解调单元（interrogator unit）的独特设计，应变速率分布式声学传感（Deformation-rate distributed acoustic sensing, DAS）可开展数据采集，其获取的地震数据与（近）弹性地面-光纤耦合场景下检波器（geophones）记录的沿光纤粒子速度运动（along-fiber particle velocity motion）等效。尽管固井井下安装场景中可轻松实现近弹性耦合，但低成本水平光纤部署场景下的实现方式尚不明确。本研究表明，通过将光纤安装并固定于浅回填沟槽（shallow backfilled trenches）中，即可实现近弹性耦合。后续可通过一维（1D）滤波，或我们优选的二维（2D）倾角速度滤波（dip-velocity filtering）方法，去除残留的无关信号。在地表与两种不同开挖深度沟槽中采集的经处理应变速率场记录，均呈现清晰的面波与折射波初至；然而，地表部署的光纤记录存在显著的时移振幅变化，对应可变的gro...