A Comparison of Prestack Depth and Prestack Time Imaging of the Paktoa Complex, Canadian Beaufort MacKenzie Basin
The Canadian Beaufort MacKenzie Basin (BMB) contains many examples on two-dimensional seismic sections of what appear to be shale diapirs or shale-cored anticlines. Devon Canada acquired three-dimensional (3-D) seismic data across one such feature called Paktoa and, in the winter of 2006, drilled an exploration well flanking the possible shale diapir. Although the well successfully tested oil from the Eocene Taglu unit, no clear evidence existed that the structure was a shale diapir instead of a shale-cored or fractured anticline.
Tests of a Kirchoff prestack depth migration (PSDM) algorithm prior to drilling had resulted in no significant improvement. Following the drilling of the Paktoa C-60 well, Applied Geophysical Services used their proprietary beam algorithm to image very steeply dipping reflectors in the core of the Paktoa structure. Interpretation of this new seismic volume shows that Paktoa is an inversion anticline, likely formed by the reactivation of an earlier extensional fault system, and not a shale diapir.
The beam PSDM took just three weeks to apply to 400 km2 (154 mi2) of marine 3-D seismic data, and the vastly improved imaging has not only changed the interpretation of the Paktoa structure but also implies that many similar features in the Canadian BMB may also be steeply dipping anticlines instead of shale diapirs or shale-cored anticlines.
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The phenomenon of rocks moving under their own means has always fascinated both scientists and nonscientists alike. The 2006 AAPG Hedberg Conference on Mobile Shale Basins was held in response to a need to gather industry and academic communities in a common forum to address the very existence of mobile shales. Stimulating and informative discussions at that Conference led to this special volume on shale tectonics. AAPG Memoir 93 documents shale tectonics from a variety of basins around the world, including the southern Beaufort Sea; the Krishna-Godavari Basin, India; eastern offshore Trinidad; offshore Brunei; and along the westernmost portion of the Mediterranean Sea. The book also provides information on the petrographic framework, behavior, geometries, and geodynamic models of shales. Publication of this Memoir coincides with a growing interest in shales as hydrocarbon reservoirs, and will add to the body of literature that significantly addresses both extrusive and intrusive shales.