Shale Gas Reservoir Families — Translating Sequence Stratigraphy into Robust Predictions of Reservoir Distribution and Potential

Bohacs, Kevin; Lazar, Remus; Ottmann, Jeff; Potma, Ken; Demko, Timothy

‘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 carbonates, and enabling transfer of lessons appropriately among plays.

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 (Bohacs, 1998). For example, in marine Constructional Shelf Margin (CSM) settings, biogenic content increases stepwise by parasequence up to the maximum-flooding downlap surface (MF-DLS) and then decreases stepwise; organic-matter type changes systematically from terrigenous, low HI proximally to marine, high HI distally. In contrast, in a Platform-Ramp (P-R) setting maximum organic-carbon content occurs in the basal TST and decreases stepwise to background levels at the MF-DLS. The lateral distribution of organic matter also differs significantly from the CSM: the P-R setting shows little or no organic-facies changes towards the limit of fine-grained deposition.

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:

1) 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, Fayetteville, Haynesville-Bossier, Eagle Ford Shales

2) Marine, Distal stacked Lowstand Systems Tracts in intra-shelfal basins (lowstand sequence set); e.g., Barnett, Floyd Shales

3) Marine, Individual Constructional Shelf Margin sequence -- upper Transgressive Systems Tract (TST) through lower Highstand Systems Tract; e.g., Niobrara, Lewis, Mowry Shale, Gammon, Cody, Mancos, Pierre, Hilliard-Baxter-Mancos, Excello Shales

4) 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.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013