Paper No. 1
Presentation Time: 8:05 AM
SHALE-GAS-RESERVOIR FAMILIES: THEIR COMMON CHARACTERISTICS AND GENETICS, ESSENTIAL DIFFERENCES, AND RECOGNITION CRITERIA
All ‘shale’ reservoirs are not the same, but neither are they all unique. ‘Shale’ reservoirs can be grouped into meaningful sets or families for analysis and comparison based on geological age, stratal stacking, and depositional setting, leveraging our long-standing approach to source rocks and carbonate reservoirs. Prolific shale-gas-play strata have several essential attributes in common: sensitively dependent on pre-existing and contemporaneous bathymetry, moderate clay-mineral content, parallel-bedded fabrics, early diagenetic cements, and significant biogenic content of both source-prone organic matter and brittle lithofacies.
Biogenic-rich rocks at the depositional sequence scale have been shown to occur in a limited number of physiographic settings, each with characteristic occurrence, stratal stacking, distribution, and character of TOC, HI, and fossil material (e.g., Bohacs, 1998). Recently, we recognized that all major shale-gas plays can be grouped into four main families, based on repeated patterns of stratal stacking of biogenic-rich physiographic settings at the sequence-set scale:
- Marine, Basal Platform-Ramp sequence overlain by one or more Distal Constructional Shelf Margin sequences (transgressive to highstand sequence set); e.g., Utica (Pt Pleasant-Flat Creek-Indian Castle), Marcellus (Union Springs-Oatka Creek-Burket), Horn River (Evie-Otter Park-Muskwa), Antrim (Norwood-Lachine-u. Antrim), Woodford (lower-middle), Fayetteville (lower-middle-upper), Haynesville-Bossier, Eagle Ford (lower-upper) Shales
- Marine, Distal stacked Lowstand Systems Tracts (LSTs) in intra-shelfal basins (lowstand sequence set); e.g., Barnett, Floyd Shales
- Marine, Individual Constructional Shelf Margin sequence -- upper Transgressive Systems Tract (TST) through lower Highstand Systems Tract (HST; distal downlap within sequence); e.g., Niobrara, Lewis, Mowry Shale, Gammon, Cody, Mancos, Pierre, Hilliard-Baxter-Mancos, Excello Shales
- Lacustrine, Balanced-Filled sequences -- transgressive to highstand sequence set; e.g., Frederick Brook Fm
This approach enables early identification of the essential elements of a shale gas play from regional context and stratal patterns that can be imaged on seismic and well-log data.