1887
Volume 22, Issue 10
  • ISSN: 0263-5046
  • E-ISSN: 1365-2397

Abstract

In this Canadian case study Dragana Todorovic-Marinic, Glenn Larson, David Gray, Scott Cheadle, Greg Soule and Ye Zheng report on their progress with a new seismic attribute in identifying productive vertically aligned fractures, cracks or micro-cracks in gas reservoirs using surface seismic data. Fractures are of great interest for hydrocarbon production. They can either hurt or help production depending on the nature of the reservoir being explored, so knowledge of their distribution and orientation can be critical to exploration success. Vertically aligned fractures, cracks or micro-cracks are known causes of Horizontal Transverse Isotropy (HTI). This type of anisotropy often has a horizontal axis aligned with open vertical fracturing that trends parallel to the maximum horizontal stress and normal to the minimum horizontal stress. It is widely recognised (e.g. Hall et al, 2000; Gray et al, 2002) that HTI anisotropy has a strong effect on the seismic amplitude. This can be measured by fitting the parameters of the Pwave Amplitude Versus Angle and Azimuth (AVAZ) equation of Rüger (1996) to surface seismic data. The outputs are seismic attributes that contain information that may be relevant to the fracturing. The P-wave reflectivity is the response of the rock to compression by the seismic wave and provides information on the rock’s lithology and fluid content. The Swave reflectivity is the response of the rock to shearing by the seismic wave and is comprised primarily of information about the lithology. The anisotropic gradient describes the variations of the AVO gradient with azimuth and is related to the crack density, i.e. to the magnitude of the differential horizontal permeability (Lynn et al, 1996). The azimuth of the anisotropic gradient is the orientation of the symmetry axis of an HTI medium. To the extent that a reservoir with vertical open fractures represents an HTI medium, the azimuth of the anisotropic gradient indicates the orientation of the fractures.

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2004-10-01
2024-03-28
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  • Article Type: Research Article
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