Integrated Fracture Characterization of Devonian Carbonate Bank — A 3-D Case Study From Alberta

Abstract

The case study covers various faults and fracture detection methods and their integration to characterize tight platform carbonates of Northwest Alberta. Trace similarity, dip attributes, volume curvature, and neural networks multi-attribute analysis is applied at the post-stack level and is then combined with the results from pre-stack Azimuthal AVO (AVAZ) and Azimuthal velocity (VVAZ) analysis. The combined integrated approach allows better continuity of interpretation work and reduces uncertainty related to each method. Many new pre-stack methods were introduced in the last decade as the extension of AVO equations, AVAZ and VVAZ started to play a significant role in determining fracture layout and the fluid content discrimination of such fractures. AVAZ takes advantage of the fact that fractured rocks perpendicular to the fractures are weaker, and therefore more compliant, than fractured rocks parallel to the fractures. So, the seismic wave striking the reservoir from different directions see different rock properties when the reservoir contains fluid filled fractures. In a similar way Velocity variation with azimuth is better understood and applied with the help of new methods of 5d interpolation and Common Offset Vector (COV) processing. To reduce the drilling risk, this study explains a workflow where pre-stack and post-stack fault and fracture analysis can co-locate the areas of gas-filled fracture zones and major stress fabric. The above described methods has been applied to the Wabamun carbonate platform of Western Canada Sedimentary Basin (WCSB), specifically in the deeper parts, west of 6th meridian. The cost to test such deeper wells is very high and thus the quantification of the attributes of the fractures within the carbonates becomes extremely important. The characterization of fractured reservoir rocks do need a more integrated approach accepting the limitations of post-stack and pre-stack analysis. By using a single space for derivation and analysis of the attributes and advanced azimuthal AVO inversion can significantly reduce the risk of exploration.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016