Depth calibration for DAS VSP: Lessons learned from two field trials

This work presents the depth calibration results of two independently conducted distributed acoustic sensing (DAS) vertical seismic profile (VSP) field trials. It describes the methods applied and shows that, contingent upon the accuracy of the well completion log, good depth calibration accuracies in the sub-meter range are attainable. Moreover, the depth discrepancies are analyzed between a conventional wireline VSP and a DAS VSP that were recorded in the same well and at the same time; the analysis shows that DAS VSP depths can be matched accurately with geophone VSP depths using solely two calibration points with known depth along the fiber optic line. This is an encouraging result because it implies that, for modern fiber optic cable installations, the DAS receiver spacing can be considered constant over large portions of the well, motivating the use of simple linear interpolation techniques to assign depth estimates to DAS channels located between calibration points.