Vertical seismic profiling using distributed acoustic sensing in a hydrofrac treatment well

Distributed Acoustic Sensing (DAS) is a Fiber Optic (FO) cable based technology which is gaining importance for VSP surveys, especially for time-lapse monitoring of reservoirs. DAS offers distinct advantages over geophones but it also poses unique challenges, including receiver depth uncertainty and low signal-to-noise ratio. Here, we present an analysis of a DAS VSP acquired for monitoring purposes in a treatment well while a multi-stage hydraulic fracture treatment was ongoing in the same well. We describe the pre-processing needed before further time-lapse analysis of the VSP. We focus on two key steps - depth calibration and noise removal. Large spike noise, most likely from the DAS acquisition system, appears to be a major source of noise in the raw DAS data, but can be removed with careful processing. Other sources of noise include temperature fluctuations in the well and optical noise. We show that excellent quality VSP data can be obtained in a hydrofrac treatment well.