Calibration of Distributed Acoustic Sensing (DAS) VSP Data

Summary The usefulness of distributed acoustic sensing (DAS) VSP data to map reservoir structures and extract rock properties is limited only by our understanding of the fidelity and characteristics of the measurement. In order to calibrate both the kinematics and dynamics of DAS VSP products, we document the correspondence of the DAS and geophones measurements for extracted slowness values, corridor stacks, amplitudes, linearity with source effort, and response to incident angle. The DAS slowness values match very well with the corresponding geophone slowness and up-scaled sonic log. The arrival times and amplitudes of the corridor stacks show a very good agreement. The average earth attenuation extracted from the first break amplitudes are nearly identical for the DAS (Q=86) and geophone (Q=88) data sets. Tests varying the source effort confirm that the DAS measurement performs linearly with seismic amplitude. We also confirm the cosine squared response of the fiber to the incident angle of the seismic wave field. These tests show that properly acquired DAS VSP data sets can be trusted for both travel times and amplitude information.