Abstract

A walkaround vertical seismic profile (VSP) survey offers full-azimuth seismic measurements for fracture or stress-field characterization near a well. Since downhole geophones may be placed close to a target zone, high quality P-wave reflection data can be obtained to study seismic amplitude anisotropy or provide key parameters for possible calibration of surface seismic amplitude versus offset and azimuth (AVOAz). This paper explores the feasibility of using a zero-offset and walkaround VSP to determine azimuthal anisotropy in P-wave reflection amplitude. The case study in the paper shows evidence of azimuthal anisotropy in the reflection amplitude observed from a fractured reservoir. A workflow is developed to extract and analyse the AVOAz data from the walkaround VSP. The results demonstrate that the walkaround VSP can provide a quantitative measure for the orientation and magnitude of fracture-induced azimuthal amplitude anisotropy. It can also provide a key data set to calibrate surface seismic amplitude, including P-wave reflection coefficients, offset-to-angle conversion, and amplitude gradients.

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