Feasibility DAS data acquisition with low power high frequency sources

Summary Distributed acoustic sensing (DAS) is notably favourable and effective in applications to borehole seismic techniques. The deployment of a fibre optic cable in a well instantly populates its entire length with seismic sensors. The deployment of a fibre optic cable in a well instantly populates its entire length with seismic sensors. This provides rapid acquisition of vertical seismic profiling (VSP) data as a single excitation of an energy source data is recorded along the full extent of the well. It also allows the utilisation of lower power sources as the time effort can be spent on a vast number of repeated excitations to accumulate sufficient data for stacking, compensating for the smaller energy release. There are many tasks, such as borehole seismic for shallow mineral wells, cross-hole studies and near-surface investigations and monitoring, where high-frequency sources are required to achieve the desired resolution. Pairing distributed acoustic sensing with high-frequency sources has many advantages. Still, it is a challenging task due to the nature of the fibre optic measurements (pulse length, gauge length, etc.). Here we present and discuss the results of a feasibility experiment utilising a high-frequency electrical sparker source and fibre optic cable cemented in a deep well. Data acquisition was complemented with recordings on a hydrophone string deployed in the same well. The study focused on optimising the recording parameters of DAS with such sources.