Multi-component corridor stacks from vertical-vibrator near-offset 3C VSP data: Tenerife oilfield, Colombia

Sayed, Ali; Stewart, Robert R.

doi:10.1190/segam2013-1383.1

Cited by 3 publications

References 7 publications

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The effect of geologic structure on fracture characterization using azimuthal vertical seismic profiles

Sayed

Stewart

2021

GEOPHYSICS

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Azimuthal VSP (AzVSP) surveys have been commonly used for fracture characterization by analyzing the P-to-S converted wave response across fractured zones. Fractured media produce characteristic two-cycle patterns on AzVSP gathers that are disrupted in the presence of complex structures. Aiming to characterize the complexity of AzVSP response in the presence of geologic structure, we derive anisotropy parameters for effective horizontal transverse isotropy (HTI) media, generate AzVSP signatures for the flat-interface case as the baseline, and compare the baseline signatures to AzVSP signatures for the dipping-interface cases. Fracture fill and fracture intensity are varied to capture the effect of intrinsic fracture parameters on AzVSP signatures. We find that dry fractures produce a stronger response compared to fluid-filled fractures for the same fracture density. The structural response on AzVSP signatures is isolated by generating synthetic seismograms across structurally equivalent isotropic models. Transverse energy, resulting from structures, could be misinterpreted as evidence for fracturing. AzVSP signatures for a fractured dipping-interface two-layer model show significant distortion of the fracture response for the 10° dip case as compared to the flat-interface signatures. As a possible solution to the structural problem, we use the arrival azimuths of the transmitted P-to-S event in synthetic signatures generated with the isotropic structural model, to orient the radial and transverse components parallel and perpendicular to the isotropic P-to-S event, respectively. Such structurally consistent orientation negates the effect of structure on azimuthal VSP gathers and uncovers the underlying fracture response. This methodology can be extended to complex overburdens that are structurally well constrained.

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