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Introduction to eolian deposition and production E.O.R.I. Minnelusa Workshop, Gillette, Wyoming
June 4, 2014
Steven G. Fryberger
The Interior, Watercolour of Oman by S.G. Fryberger
An review of basic principles of eolian deposition, with illustrations from the modern and ancient sediments.
ICE HOUSE
GLACIERS
GREEN HOUSE
The Big Picture: EOLIAN QUARTZOSE SAND SEAS THROUGH TIME
100
50
150
200
250
300
350
400
450
500
550
TEMP SEA LEVEL
PRE CAMBRIAN
TER
COASTAL CONTINENTAL Low relief High relief High relief low relief
Tensleep-Weber
Toroweap-Coconino-Lyons-De Chelly
Bigbear
Miqrat
Avile Etjo
Sherwood
Unayzah
Barun Goyot
Navajo-Nugget-Aztec
Leo
Keuper
Entrada continental
Wingate
Minnelusa-Ingleside-Casper
Waterberg Supergroup
Merrimelia
?
AUK
Amin
WAHIBA SANDS
Entrada coastal
Dynamic sand sea sedimentology model: Distinct facies of eolian sand seas stack through lateral migration
Aeolian sand seas as a whole may have facies belts based on net sand sea migration, or net evolution.
Eolian sand sea formation:
Wind , topography, and sediment supply interact to deposit sand seas over long periods of time, commonly in an on-again, off-again manner.
Eolian sand sea formation: Depending upon distance of sand migration from source, trap-biased or source-biased sand seas will form
Eolian sand sea creation
Complex interactions of wind, rainfall belts, and water bodies also can create and define sand seas
Mauritania
Minnelusa model?
Eolian deposits are built from four facies groups: Dune, interdune, sand sheet and sabkha
Rapid changes in eolian facies can occur within a single oil or gas field, influencing recovery factors
Basic Dune Forms are barchan, linear and star They result from differences in wind regime.
Barchan 1 wind
Linear 2 winds
Star 3 winds
Dune sub-types have distinct stratification styles. Result of morphology and process framework
Barchanoid dune sub-types
Idealized barchan dune cross-section along the wind: Drawing shows geomorphic, structural and genetic terms. It is important to keep distinction clear in core description.
Always start with genetic terms, the least interpretive description
Eolian stacking patterns can be complex Eolian bedforms rarely stack in complete sequences
The cartoon world . . .
The real world . . . .
Ancient example Navajo Sandstone: eolian sequences represent the stacking of only portions of dunes, or other eolian facies
Internal stratification of aeolian dunes is a direct reflection of the wind regime and the growth seasons of the dune.
Nebraska Sand Hills, barchanoid dune
Libya, Linear dune
wind
Studies of modern dunes shows that cross-bedding patterns are probably complex in the subsurface.
Eolian primary strata The type of primary eolian stratum is an important control on reservoir permeability.
Drivers: texture, mineralogy, cements of strata types.
avalanche and grainfall: well sorted, largest grains
Ripple, moderate sorting, pin stripes reduce vertical permeability
dry interdune and sabkha: evaporites and clays, poor sorting
Very good reservoir
Bad reservoir
Eolian primary strata types are defined by process and wind
Process: mass flows versus ballistic effects with ripples, and grainfall through still air in lee of dune
Wind direction and strength variability, many time scales minutes, hours, days, months, years
SHOREFACE
INTERDUNE AND EXTRADUNE
DUNE
Dune strata commonly have better poroperm characteristics than interdune or extradune strata
Primary strata occur as bundles in dunes and interdunes: Differing permeabilites may cause sweep inefficiency
After Lindquist, 1988
K MIN
K MAX
K INT
Key permeability directions Always use data from core and dipmeter when planning secondary operations
After Krystinik, 1990
Core example from Permian Rotliegend Fm. Auk Field, North Sea There is a strong permeability contrast between ripple and avalanche strata
Tight, red-bed ripple strata
Porous, oil-stained avalanche strata
White, cemented, tight ripple strata
Depth (ft.)
Auk Field Well 30/16-3
POR PERM
Core example from Auk Field, Permian Rotliegend, UK North Sea
Porous, permeable avalanche strata- oil saturated
Tight ripple strata – red-beds
POR PERM Permeability contrasts compartmentalize eolian reservoirs at laminar scale
Sandflow toe
100-200 Md perm 1
met
re
Thin eolian sedimentary units can exist as highly permeable flow units
avalanche strata
4750 m depth +/-
Cambrian Amin Formation: Oman
Nugget Sandstone, Utah Flow barriers are created by discontinuities of primary strata, as
well as higher-order stratigraphic breaks
after Lindquist, 1988
Permeability anisotropy in the Nugget Sandstone after Lindquist, 1988
Minnelusa core Raven Creek Field small scale heterogeneity
Anhydrite-cemented dune Oil stained sand
•Complex time-structure of Wahiba dune field, and therefore of ancient aeolian reservoirs.
•Build-and-fill model of aeolian reservoirs: implications for production.
•Re-cycling of aeolian sand into fluvial deposits: importance of sediment pedigrees.
•Common existence of thin, highly permeable eolian thief zones that reduce sweep efficiency.
New concepts for eolian reservoirs, illustrated by analogues from the modern Wahiba Sands of Oman
The Wahiba Sands, Oman
AL JABIN QAHID AL HIBAL
MODERN LINEAR MEGADUNES AND REWORKED SAND
WEST EAST OCEAN W ANDAM
AFTER RADIES, ET AL, 2004
The Wahiba Sand Sea has a complex time-structure Discontinuous deposition, incomplete preservation
Wadi Batha channel margin
Wadi Batha
Wahiba Megadunes
E W150Ka 2 Ka 16-19 Ka10 Ka
110 Ka
Oasis8 Ka10-23 Ka
32Ka36 Ka40 Ka
112 Ka
229 Ka
N S NS
Wadi Beach
Slight high of older rocks
Old W
adi Wahiba
beneath dune sands
Slight high of older rocks
Ras Ruways Arabian
Sea
25 Ka
Oman Mountains
A’
A A’
A
Wahiba Sand Sea: stratigraphy compared to age dates of the Wahiba Sands
Age dates from the Wahiba Sands
If the Wahibas were preserved as an oil reservoir, they might be viewed as a single sandstone . . . and thus a single flow unit with a simple history.
Geologists typical perspective, first well in an eolian reservoir
229 K
today
WAHIBA SAND SEA EXPRESSED IN TIME
OCEAN
OXYGEN 18
O
AL JABIN
QAHID
AL HIBAL
GLACIAL
Rel
ativ
e Ti
me
Scal
e Today
229 K
Glacial cycles
Different levels of the dune field were deposited at different times, under very different conditions. Useful reservoir analogues exist at these different levels.
However, the truth would be different. . . .
Cross Section Gibbs to Little Mitchell Creek
Build-and-fill controls oil fields, Minnelusa Formation
Minnelusa 3D model from wells created in Petrel by Nick Jones
Little Mitchell Creek B Sand Oil Field
T 52N
R 69W
Thick
Thin
Gibbs B Sand Oil Field
Cross section next slide
B Sand isopach
Build-and-fill of geomorphic accomodation space, Minnelusa Formation
Minnelusa 3D model from wells created in Petrel by Nick Jones
Thick
Thin
Gibbs B Sand Oil Field
Little Mitchell Creek B Sand Oil Field
Upper B Sand
Preserved geomorphic relief on the B sand has trapped oil at Gibbs and L. Mitchell Creek
Minnelusa 3D model from wells created in Petrel by Nick Jones
Cross Section West Gibbs to Bracken
Build-and-fill controls Upper B sand oil fields, Minnelusa Formation
Cross section next slide
T 52N
R 69W
Thick
Thin
West Gibbs Upper B Sand Oil Field Bracken Upper B Sand Oil Field
Minnelusa 3D model from wells created in Petrel by Nick Jones
Minnelusa 3D model from wells created in Petrel by Nick Jones
Thick
Thin
West Gibbs Upper B Sand Oil Field
Bracken Upper B Sand Oil Field
Thick B Sand
Thick B Sand
Thick C Sand
Build-and-fill of geomorphic accomodation space, Minnelusa Formation Preserved geomorphic relief on the B sand created space for Upper B Sands
•Inherited linear dunes: = BAD ROCK •Infill by younger barchans= GOOD ROCK
Linear Megadunes are reworked into barchan dunes that fill earlier-created accommodation space
Barchanoid dunes
Older Linear Megadunes
Wahiba Sands –Build-and-fill eolian reservoir/ flow unit creation
eolian geomorphology in a dynamic world: Dune fields interact with nearby depositional environments, producing
complex sediment pedigrees and packages
Some eolian sedimentary units are thin and permeable. They can intercalate with less permeable deposits
A B
C D
Effects of floods in Wadi Batha. A, strong currents along western side of Wadi Batha have built the gravel bar in the foreground composed of dolomite, limestone, ophiolite and other darker mineral clasts. Waters have eroded the downwind end of linear megadune, causing collapse of sand into the floodwaters and re-cycling into the fluvial domain. B, ponding of muddy floodwaters in an interdune along the northern margin of the megadunes. C, fluvial bar from earlier flood cut by recent flood, view to NW. D, after waters have receded, mud dries with some light colour due to light clays from Barzamanite outcrops weathered upstream and thin salts. View is across Wadi Batha toward the south-southwest.
Eolian sand is recycled into fluvial deposits along Wadi Batha, Oman
A B
Wadi Batha following flooding. A, view to the southeast showing flooded channel and mud draped over sandy bottom. B, pools of drying water amid various eolian and fluvial bedforms that have been draped with a thick layer of fresh mud. Small ripple forms are fluvial. Larger forms associated with shrubs may be eolian coppice dunes freshly draped with mud. Sand sheet in background (arrow) has remained clear of the flood.
Flooded sand sheet
Further process examples: re-cycling of eolian sand into fluvial deposits, Wadi Batha, Oman
Effects of floods in Wadi Batha after the water dries. A, eolian processes begin to take over Wadi Batha as dunes and loose sand are deposited over fresh mud cracks. B, Cliff cut by flood fills with windblown sand from the south (right). C, drying has caused some light evaporites and clays to whiten on the surface of the Wadi in the interdune where the waters ponded (see Figure 49B above for overview). Muds drape earlier topography caused by stream erosion during the flood’s maximum flow. (note curving channel in foreground). D, flood-and-dry regime leads to small-scale interbedding of eolian dune and fluvial pebbles .
A B
C D
Dune slipface
Fluvial pebbles, mud clasts
Further process examples: Wadi Batha, Oman
A B
Fluvial and recycled eolian sediments interbedded in Wadi Batha. A, red eolian sand re-deposited by floodwaters is intercalated with dark fluvial gravels and sands. Note red colour of dune sand in background. B, closer to the dune field, dark gravels form a single layer between beds of fluvially recycled eolian sands with small pebbles and mud clasts.
Re-cycling of eolian sand into fluvial deposits, Wadi Batha, Oman
Fluvial re-cycling of eolian sand. A, Mid-channel bar comprising fluvially recycled reddish eolian sand with climbing ripple structures, pebbles and slump structures flanked by gravel transported from mountains; mainly dolomitic and ophiolitic grains with some limestones. B, Dark gravels overlie much finer, better-sorted, reddish recycled eolian sand with small pebbles below white dashed line. Gray unit below is primary (non-recycled) eolian strata.
A
Primary eolian
Recycled eolian with pebbles
Light mud from flood and dry
B
Fluvial systems will pick up eolian sands, improving texture
Interbedding of eolian (?) and fluvial sands. A, overview of a trench in the wadi channel not far from the edge of a dune. B, detail of trench showing eolian (?) units (base of trench) overlain by fluvial gravels and recycled eolian sands with pebbles.
A B
eolian ?
mud
Eolian sand from nearby dunes may be recycled into very clean, “eolian looking” fluvial sandstones
Miqrat Formation outcrops, Huqf area, Oman
Clean white sheetflood sand
Clean sheetflood sand
Huqf Miqrat outcrops have porous sheetflood sands recycled in part from eolian dunes. These are interbedded with impermeable, or low permeability red beds.
Playa facies, haloturbated
The pedigree of a fluvial (or shoreline) sand may include an eolian history
The Cambrian Miqrat sheetflood sands have many rounded, frosted “aeolian” appearing sand grains, and little clay. Nearby outcrops have interbedded eolian dunes. (Huqf area)
Small dune
Clean sheetflood sand
Playa- evaporitic
Thin eolian sands within sheetflood deposits
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Useful References