Reservoir Characterization of Ardley Coals, Scollard Formation, Alberta: Borehole Image Interpretation
Strata of the Ardley coal zone in the Upper Cretaceous Scollard Formation in the Western Canada Sedimentary Basin are targets for coalbed methane exploration. High-resolution reservoir characterization of Ardley coals and adjacent sandstones and mudstones is facilitated by electrical borehole measurements made with the Formation Micro-Imager (FMI*) tool. Unique reservoir characteristics provided by FMI interpretation include dip and strike of beds, sedimentary structures, faults, and fractures. Image interpretation can differentiate mineralized from non-mineralized (open) fractures and resolve very thin interbeds in all lithotypes.
Stratal geometries in the Scollard Formation assist deduction of the environments of deposition of these coal-bearing strata. Interpretation of genetic surfaces within sandstones, including scours and crossbeds, facilitates determination of channel orientation and paleo-streamflow direction. In addition, internal heterogeneities can be visualized and potential reservoir compartmentalization can be understood. Quantitative assessment of thin partings and mineralized fractures, both of which degrade coalbed reservoir permeability, can be visualized on borehole images and their effects on reservoir heterogeneity fully appreciated. Interpretation of natural and drilling-induced fractures and borehole breakouts yield important clues to stress orientation and stress anisotropy in the subsurface. Fracture and coal cleat orientations from FMI interpretation are consistent with outcrop cleat measurements (Faraj, 2004, CSUG) and those determined in the subsurface from oriented cores. Indications of maximum and minimum horizontal stresses from borehole image interpretation are consistent with published orientations (Bell et al, 1994, CSPG) in the Western Canada Sedimentary Basin. Cleat orientation, spacing, and mineralization affect the design of horizontal wells and vertical pilot projects.
*mark of Schlumberger
Natural Gas from Coal and Shale II
2005 AAPG Annual Convention (June 19-22, 2005) Technical Program