The Less Conventional Side of Carbonates
James Bishop1, Ted Playton1,$, Paul (Mitch) Harris1,*, Paul Landis2,#, CJ Lipinski1, Frank Harris1,^
1Chevron - Energy Technology Company
2 Chevron North America Exploration & Production Company
$ TengizChevroil, Kazakhstan
*CSL – Center for Carbonate Research, University of Miami
# Chevron - Global Exploration
^Retired, Chevron - Energy Technology Company
Carbonates are a significant component of many unconventional accumulations—a diverse group of continuous and tight reservoirs. Though differing in trapping mechanism, these reservoir types share a diverse grain assemblage, complex pore systems, and a need for well stimulation. Such reservoirs have dramatically changed the energy landscape in North America and are expected to be a focus for industry in the coming years. However, currently there is little geologic framework with which to view unconventional carbonate accumulations, their exploration and exploitation. Many plays are viewed simply as engineering challenges; developing an appropriate geologic context for these plays presents a significant opportunity for more rapid appraisal and efficient development.
This study provides a survey and classification of unconventional carbonate reservoirs. The survey of plays addresses variations in lithology, sources for carbonate content, dominant depositional processes, sequence architecture, organic richness, and pore types.
Unconventional carbonate plays are then classified into five groups, using case studies to illustrate common characteristics. Classes include Platform Top (Bend, Permian Basin), Platform Margin/Slope (Tengiz, conventional, Pricaspian Basin), Basin Edge (Wolfcamp, Midland Basin), Basin Center (Duvernay, Western Canada Sedimentary Basin), and Drowned Platforms (Eagle Ford, Gulf of Mexico). The end-member deposit ‘classes’ are reflected in the configurations of source and reservoir, trends in carbonate sedimentation, models for basin anoxia, and in differing pore systems.