Characterization of Slope and Basin Facies Tracts, Jackfork Group, Arkansas, with Applications WR Deepwater (Turbidite) Reservoir Management
Published:December 01, 2000
Roger M. Slatt, Charles G. Stone, Paul Weimer, 2000. "Characterization of Slope and Basin Facies Tracts, Jackfork Group, Arkansas, with Applications WR Deepwater (Turbidite) Reservoir Management", Deep-Water Reservoirs of the World, Paul Weimer
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Characterization of 15 stratigraphic sections of the Pennsylvanian Jackfork Group deepwater (turbidite) deposits of Arkansas have provided a set of criteria to distinguish an updip slope facies tract from a downdip basinal facies tract. The updip facies tract is characterized by lenticular sandstone packages with internal thick-bedded, lenticular to sheet sandstones, associated muddy debrites, and other ‘disturbed’ strata. Characteristic features at a smaller scale include (a) irregular upper and lower slumped/scoured surfaces of beds, (b) stretched, distorted, and contorted shales, (c) a wide variety of lithofacies, including muddy debrites and pseudo-conglomerates or breccias, (d) common shale rip-up clasts in sandstones, (e) non-systematic vertical stacking of diverse facies, and (f) overall fining- and thinning-upward stratification pattern. Lenticular, channel-fill sandstones generally comprise >50% of the sandstone strata.
By contrast, the downdip basinal facies tract is characterized by evenly-bedded sheet sandstones, as well as thinner channel-fill sandstones in variable proportions. Characteristic features at a smaller scale include (a) flat-based, thick amalgamated and layered sheet sandstones with fewer erosional bases and slumped/scoured tops, (b) relatively good lateral continuity, (c) compensation style deposition, (d) relatively fewer muddy debrites, (e) laminated shales and mudstones, and (f) relatively ordered vertical stacking of strata.
Sandstone packages within the downdip basinal facies tract thin at rates on the order of 0.40%. Individual sandstone beds thin at appreciably lower rates of < 0.1%. Thus, sheet sandstone beds can be continuous for thousands of feet and packages of beds can be continuous for miles.
Many of the sedimentologic and stratigraphic criteria for distinguishing these updip and downdip facies tracts can be identified in core or borehole-image logs from subsurface reservoirs, in order to better understand reservoir characteristics and architecture.
The architectural differences between updip and downdip facies tracts indicate that in analog reservoirs, different development and management scenarios should be employed to maximize production. Owing to lateral and vertical discontinuities and internal complexities in the updip facies tract, wells should be more closely spaced in order to maximize primary or secondary recovery. In the more continuous downdip facies tract, wells can be drilled at larger, more economical spacing and hydrocarbons can be produced more easily in both primary and secondary recovery modes.