AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

An Integrated Approach to Characterizing Brecciated Carbonate Reservoir Facies Using Borehole Image and Core Data in the Grosmont Platform: A Giant Heavy-Oil Resource in Alberta, Canada


Examples demonstrating the application of borehole image logs (BHI) in brecciated reservoir facies are uncommon despite their growing importance as unconventional resource plays. The Upper Devonian-aged Grosmont Platform in Alberta, Canada, is one such reservoir system, where Upper Ireton unit objectives are fractured and dolomitized shallow-marine carbonates that were subsequently intrastratally brecciated. Here, we focus on describing the heterogeneity of imagable rock fabrics and structures from vertical and horizontal wellbores. Further, we link BHI data to core observations and demonstrate how image analysis has helped define the local framework. In vertical wellbores, brecciated intervals are identified as meter-scale, mottled image maps and chaotic zones of randomly-dipping deformed beds which occur in otherwise monoclinal, predominantly southwesterly-dipping strata. In horizontal wells, these discontinuous breccias zones can be tens of meters in measured length and are usually bound by high-angle planar surfaces internal to which are resistive, medium- to large-scale, angular- to sub-rounded features supported by a conductive matrix. Within many of the resistive features are conductive planar surfaces and parallel lamina. Together, the resistive features and internal conductive traces are interpreted as dolomitic clasts preserving primary sedimentary structures and occluded, pre-karst fracturing. Conductive traces of varying width are also observed crosscutting the circumference of the borehole and examples with- and without displacement across the feature are common. Cores collected in vertical wellbores support many BHI observations and identify minor faulting and the dolomitic, angular nature of the clasts. When integrated into local models, the observations and feature statistics derived from core and BHI analysis have been useful in defining the extent of brecciation, the distinction of features internal- and external-to brecciated intervals, and the orientation of tectonic and atectonic fractures. Recognition of different rock types and fracture characterization methods have been critical to our ongoing static and dynamic modeling approach.