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Seismically-Derived Fracture Mapping for Unconventional Reservoir Exploitation

George Bunge
Schlumberger Ltd.

Knowledge of the pre-existing natural fracture orientations and of the in-situ stress regime has particular relevance for optimal well planning and completions in unconventional reservoir plays. Surface seismic data offers the potential to provide this information, enabling field development planning prior to the onset of the drilling campaign. At the ´meso´ scale, where fractures are of a sufficient size to cause discontinuities in the seismic image, though are not necessarily clearly resolvable, Ant-Tracking can offer a solution. This provides a means of rapidly obtaining detailed, automatic unbiased fault and fracture interpretation from seismic amplitude data which integrated with fracture information derived from well log measurements and/or microseismic data, enables a detailed understanding of geometries associated with fault/fracture networks. It is particularly powerful in terms of capturing small-scale, often subtle discontinuities which normal interpretation cannot realistically capture. At the ´micro´ scale, below the limit of seismic resolution in terms of imaging, of even subtle discontinuities, we can utilize seismic anisotropy. Shear waves generated by the interaction of incident P-wave energy propagating through a fractured media, are polarized into a fast component – along the dominant fracture direction, and a slow component perpendicular to it. Pre-stack simultaneous AVOAz inversion provides estimates of this shear wave anisotropy with potentially more detail of the vertical variations because of the sensitivity of shear to interface contrasts rather than an average cumulative response of overlying strata associated with velocity based P-wave anisotropy. This information can be used to infer the fracture density and the orientation of the dominant fracture direction. We present examples of these techniques from several unconventional plays in North America.

AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013