Depth registration of VSP DAS fiber

Abstract

As part of the continuous monitoring program implemented at the CO2 injection site developed by Containment and Monitoring Institute, two Vertical Seismic Profiles (VSP) surveys were acquired at the Field Research Station (FRS) in Newell County, Alberta, Canada. The surveys were recorded with two different receiver types; a 24-level 3C geophone array and an integrated fibre optic cable, both Distributed Acoustic Sensing (DAS) and Distributed Temperature Sensing (DTS). A calibration step is necessary to register the precise depth of the DAS traces acquired with the straight fibre optic cable. This calibration consisted on two approaches; a cross-correlation based method and a time difference analysis between the DAS and geophone data. The cross-correlation results indicate an accurate depth registration of the DAS data with respect to the geophone data. A difference of 1 m was obtained for the straight fibre raw data. While the time difference analysis shows a similar result, a difference of 1.25 m for the straight cable. Furthermore, the DAS data was converted to geophone equivalent values through integration for comparison and a more accurate result was obtained for l the DAS data after the calibration workflow. In addition, a synthetic seismogram was generated and compared with corridor stacks obtained from a zero-offset DAS and geophone data processing.