Mitigation of Zigzag Noise on DAS VSP Records Acquired in Vertical Wells

Summary Fiber-optic cables deployed by means of wireline or coiled tubing in vertical wells can exhibit zones where the cable is not acoustically coupled to the formation or casing. In these situations, a reverberating noise train, commonly referred to as zigzag noise, appears in the distributed acoustic sensing vertical seismic profile records in zones with poor coupling. This noise propagates trapped in this uncoupled zone, first down the cable and then back upwards, with low losses making it a time persistent problem. No universal solution has been determined to help mitigate this noise. A novel method is proposed to first identify the noise characteristics, and then adaptively subtract an estimate of the noise from the records. The methodology is explained and examples provided, demonstrating its effectiveness to help mitigate the noise.