Abstract

Because of their potentially large volumes and excellent reservoir properties, winglike clastic intrusion complexes may represent stand-alone exploration targets. However, determining the three-dimensional (3-D) geometry of such complexes is problematic because of limited exposure in the field and insufficient seismic resolution and well coverage in the subsurface. In this study, high-quality 3-D seismic reflection data from offshore Norway are used to determine the 3-D geometry of winglike intrusion complexes adjacent to a deep-water slope-channel complex. Intrusions form sheets or “wings” that are developed almost continuously along both margins of the 15-km (9-mi)-long channel complex. Intrusions dip up to 20° (more commonly <10°), crosscut up to 90 m (30 ft) (undecompacted) of the overlying stratigraphy and extend up to 1095 m (3593 ft) away from the channel complex. Three styles of intrusion are observed: type 1: dikes lacking sills at their upper tips; type 2: dikes that pass upward into sills at their upper tips; and type 3: “stepped sills” that consist of linked sill and dike segments. These different styles of intrusions pass laterally into one another, leading to extreme complexity both between and along-strike individual intrusion complexes. Although the mechanisms driving initial overpressure development and injection itself are unclear, this study indicates that 3-D seismic data are a powerful tool in understanding the 3-D geometry of winglike clastic injection complexes and suggests that the true geometry of these features is more complex than previously documented. This study also has implications for potential reservoir geometries and hydrocarbon exploitation of winglike clastic intrusion complexes.

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