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
ground-fiber coupling due to air-temperature fluctuations about 0ºC. These
results indicate that ground freezing provides improved but more complex
fiber coupling.

变形率分布式声学传感（DAS）借助部分解调仪单元的独特设计得以实现，在（近）弹性地-纤耦合场景下，可获取与检波器记录的沿光纤质点速度运动等效的地震数据。尽管近弹性耦合在固井井下安装中易于实现，但在低成本水平光纤部署中如何达成这一目标尚不明确。本研究表明，通过在浅回填沟槽中铺设光纤并冻结，可实现近弹性耦合。随后，可通过一维滤波或我们推荐的二维倾角-速度滤波方法去除残余干扰信号。在地表及两种不同沟槽深度处采集的经处理的变形率场记录，显示出清晰的面波和折射波到达信号；然而，地表部署的光纤记录因气温在0℃左右波动导致地-纤耦合变化，呈现出显著的时移振幅变化。这些结果表明，地面冻结可改善光纤耦合效果，但也使耦合过程更为复杂。