Observing Fracture Lineaments with Euler Curvature

Over the last several years, seismic curvature attributes have been shown to be very useful in the interpretation of flexures and folds which can often be associated with conjugate faults and fractures. Although many curvature measures that have been introduced, we find the most-positive and most-negative principal curvatures k1 and k2 to be the most useful. All other curvature attributes can be derived from the two principal curvatures. For example, some practitioners have found that the components of apparent curvature projected parallel to the dip azimuth and strike of a dipping plane to be useful in given tectonic and stress settings.

In this study we describe the theory and application of Euler curvature, which is a generalization of the dip and strike components of curvature in any user-defined direction, to the interpretation of surface seismic data. Since reflector dip magnitude and azimuth can vary considerably across a seismic survey, it is more useful to equally sample azimuths of Euler curvature on the horizontal x-y plane, project these lines onto the local dipping plane of the reflector, and compute Euler curvature along a given strike direction.

We describe here the application of Euler curvature to two different 3D seismic volumes from northeast British Columbia, Canada and show that this attribute is useful for the interpretation of lineament features in desired azimuthal directions.

Ideally, one would process and migrate the prestack seismic data into vector tiles and examine each sub-volume for lineaments perpendicular to a given tile azimuth. Unfortunately, such analysis requires carefully-designed, rather expensive, wide azimuth acquisition. The Euler curvature attribute has the advantage that it can be computed from the conventional final migrated stacked volume to obtain the attributes in different azimuthal directions. Depending on the objective, one can generate long- or the short-wavelength computations. In this manner, azimuthally-dependent lineament intensity volumes can be correlated to natural and induced fractures seen in image logs to better quantify the presence of natural fracture sweet spots perpendicular to today’s minimum horizontal stress field.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California