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