Nugget Formation Reservoir Characteristics Affecting Production in the Overthrust Belt of Southwestern Wyoming

Abstract

The Jurassic/Triassic Age Nugget sandstone of the southwestern Wyoming overthrust belt is a texturally heterogeneous reservoir with anisotropic properties that have been inherited primarily from the depositional environment but also have been modified by diagenesis and overprinted by tectonism.Predominantly eolian processes deposited crossbedded, low-angle to horizontally bedded and rippled, veryfine-to coarse-grained sand in dunes, interdune areas, and associated environments. Original reservoir quality has been somewhat modified by compaction, cementation, dissolution, clay mineralization, and the precipitation or emplacement of hydrocarbon asphaltenes or residues. Low-permeability gouge-and carbonate-filled fractures potentially restrict hydrocarbon distribution and negatively affect producibility, whereas discontinuous open fractures enhance permeability in some intervals. Contrast in air permeability between dune and interdune deposits ranges over four to five orders of magnitude. Dune and interdune intervals are correlatable locally with the aid of core log, conventional log, and stratigraphic dipmeter data. Stratigraphic correlations then can be utilized to model the lateral and vertical extent of directional properties in the reservoir.

The Mississippian Loyalhanna Limestone (Formation); a Paleozoic eolianite in the Appalachian Basin (in Cecil, C.B., ed., Predictive stratigraphic analyses guidebook series No. 1, The Mississippian and Pennsylvanian systems in West Virginia)

“…The complexities of producing hydrocarbons from dune-interdune and dune-extradune sequences is well documented in the literature (e.g. Lupe and Ahlbrandt, 1979;Lindquist, 1983;Glennie, 1983;Fryberger, 1984;Goggin and others, 1988;Chandler and others, 1989;Krystinik, 1990;Panda and Lake, 1994;Ahlbrandt and others, 1994;Shebl and Surdam, in press). If such fluid flow, sequence stratigraphic and depositional models are reapplied to the Loyalhanna, considerable revaluation of its resource potential and field growth may occur as has been the experience of petroleum producing eolianites in Colorado and Wyoming (Ahlbrandt and Fryberger, 1982;Krystinik, 1990).…”

Major Oil Plays in Utah and Vicinity

“…The dune/interdune sequence generally consists of fine-to coarse-grained, subangular to subrounded sand or silt grains cemented by calcite (Picard, 1975). The best permeability is along bounding surfaces (bedding planes), with preferred directions along the dip and strike of the individual slipfaces (cross-beds) (Lindquist, 1983).…”

“…Dune sand-flow toes often form tangential contacts of cross-beds with the lower bounding surfaces (Ahlbrandt and Frybreger, 1982). Dune lithofacies from the brink to the toe of the dune slipface consist of (1) thin, reverse graded, tabular, pinstriped grainfall laminae, (2) thick, subgraded avalanche laminae, and (3) thin, tightly packed, reworked ripple strata at the dune toe (Lindquist, 1983). Wind ripples or high-index ripples are occasionally preserved on topset deposits.…”

“…The low-permeability interdune lithofacies is a potential barrier to flow. Identification and correlation of dune/interdune lithofacies in individual Nugget reservoirs in the thrust belt is critical to understanding their effects on production rates and paths of petroleum movement (Lindquist, 1983). Avalanche laminae, soft-sediment deformation, and other depositional features can also result in significant reservoir heterogeneity, even within the dune lithofacies.…”

Modelling fine-scale heterogeneity for optimal history matching from aeolian gas reservoirs, Neptune Field, UKCS

“…Toaccommodatethisinterpretation aseto f stochastic models wasconstructed to test the impacto ffine-scale heterogeneity for fielddevelopment. Earlierworkshavedescribed indetaillaminato bedform scalesofpermeability heterogeneity in aeolians andstonesandtheircontrols (Lindquist 1983(Lindquist ,1988Chandler etal .1 988;Goggin etal .1 988;Heward1991) and methodso fmodellingsuch systems usingsequentialindicator simulation (Cox etal .1994;Sweet etal .1996;Sweet1997). Inthis paper,amethodisdescribed thatcapturesfine-scalepermeability characteru singsmall-scaleg eopseudo-models andi ncorporates thesei nto object-based models withobject-specific permeability profiles.…”