Unraveling the Pennsylvanian

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Unraveling the Pennsylvanian

• Wayne R. Wright
• Bureau of Economic Geology
• Jackson School of Geosciences
• University of Texas at Austin

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MorrowanAtokanDesmoinesian
MissourianVirgilian
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(No Transcript)
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Morrowan
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Regional Sedimentation Patterns

• Morrowan age siliciclastics dominate deposition
  in the west of the Permian Basin whereas
  carbonate deposition dominates in the east
• 2nd-order transgression from siliciclastic
  fluvial deltaic to shallow marine and
  subsequently to carbonate deposition in the
  western Permian Basin.

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MorrowanSiliciclastics
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MORROWAN SILICICLASTICS

• Large incised valley-fill system.
• An up-dip to down-dip transition from fluvial and
  deltaic to estuarine and open marine facies.
• Excellent reservoir potential is apparent in
  amalgamated, stacked channel systems and bay head
  deltas.
• Conduits for shelf margin bypass during periods
  of lowstand. Such bypass channels may have fed
  sediment into the deeper basin resulting in
  lowstand slope and basin floor fan deposits.

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Old 3 Zone Model
Upper (carbonate)Middle (siliciclastic) Lower
(siliciclastic)
(After Mazzulo, 1984)
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Revised Model(Icehouse Conditions)
Old Model(Greenhouse Conditions)
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Segment 3
(after Bowen and Weimer, 2003)
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Proximal Segment 2

• In the transitional facies towards the down-dip
  estuarine section, fluvial channels are separated
  by lower quality reservoir estuarine sands and
  reservoir quality, especially permeability, is
  decreased in these thinner more marine facies.

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Proximal Segment 2
(after Bowen and Weimer, 2003)
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Distal Segment 2

• In the down-dip facies tract (estuarine),
  reservoir facies are sparsely developed fluvial
  channels are narrow, disconnected, thin and
  separated by thick estuarine basin shales.
  Down-dip bayfill deltas have excellent reservoir
  quality and targeting potential.

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Distal Segment 2
(after Bowen and Weimer, 2003)
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Ichnofacies and Stratigraphy
(after Buatois et al., 2002)
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• Diagenesis Dissolution of detrital grains and
  authigenic clays generating secondary porosity
  and permeability is very important to development
  of good reservoir quality, especially in the more
  estuarine to marine sands. Middle Morrow
  sandstones are more compositionally variable and
  provide the best production.

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PERMIAN BASINDATA
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Red box outlines the area of a previous
interpretation that depicted a shore parallel
lower Morrow facies belt overlain by a middle
Morrow facies belt prograding basinwards.
(modified after James, 1985)
Northwest Shelf
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Permian Basin Incised Valley
Bay-head Delta System
Empire Field (Eddy Co.)
100ft
60ft Incision
(after Lambert, 1989)
Incised Valley Complex
8.5 miles/15.8 kilometers
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Seismic Stratigraphy
Composite Sequence Boundary (Chester/Barnett and
lower and upper Morrow Fm.
2 miles/ 3.7 km
(after Van Dock and Gaiser, 2002)
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Key Points on Siliciclastic Deposition

• Scale and Stacking Patterns In icehouse times,
  such as the Pennsylvanian, higher order eustatic
  fluctuations can dominate over the lower order
  oscillations (e.g. extensive progradation during
  transgression).
• Stacking patterns and facies tracts in icehouse
  systems may have substantially different
  geometries than greenhouse systems.
• For example, the dip length of a 4th order
  fluvial system deposited during icehouse
  conditions is 3 times longer than the equivalent
  3rd order cycle in a green house setting.

• Sediment Supply Sediment supply may be the
  largest controlling factor in Morrow
  siliciclastic sedimentation patterns. Extremely
  high and/or low sedimentation rates can produce
  sequence and facies stacking patterns that are
  quite different from those developed during more
  normal rates of sedimentation.

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MorrowanCarbonates
(dominantly eastern Permian Basin)
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Morrowan Carbonate Deposition

• Deposition of the Upper Morrowan carbonate unit
  in the Delaware Basin and Northwest Shelf area
  indicates a switch from local tectonic to
  regional eustatic control as tectonism decreased
  in the hinterland and sediment supply diminished.
  
• It appears that carbonate deposition occurred
  over a much larger area in the Permian Basin
  (Eastern Shelf and Delaware Basin) than
  previously documented.
• Algally dominated bioherms and higher energy
  facies (ooid grainstones) containing fracture
  porosity are potentially overlooked reservoirs.
  With the current explosion of interest in the
  shale gas systems (primarily the Barnett but also
  the Smithwick) the overlying carbonate system are
  potential fractured reservoirs for expulsed
  Barnett gas.

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Lower Marble Falls Fm.

• The Llano uplift (Morrowan age) carbonate
  succession including the Lower Marble Falls Fm.
  is an analogue for the equivalent sections in the
  Permian Basin
• What is it???

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Stratigraphy of the Llano Uplift and Eastern Shelf
(after Erlich and Coleman, 2005)
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Outcrop Analogue
1m

• Regionally, the Lower Marble Falls bioherms
  contain Cuneiphycus (red algae) and rarer
  Donezella boundstones ranging in thickness from
  1-10m. Oolitic grainstones and phylloid algae
  wackestone/packstones are also common.
  Spiculite-bearing facies dominate the
  off-platform/ramp and intermound (biohermal)
  areas.

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Morrowan Carbonates

• Bioherm dimensions
• Can reach 200ft/60m coalesced thickness with
  widths of 2000ft/610m in an ovoid shape
• Are producing intervals
• Generally fracture porosity augmented by primary
  intergranular and shelter porosity
• Hands on look at Morrowan carbonates

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Early Morrowan Paleogeography
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Atokan
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Regional Sedimentation Patterns

• Atokan age siliciclastics dominated deposition in
  the west of the Permian Basin whereas carbonate
  deposition dominated in the remainder of the
  basin
• 2nd-order transgression
• aerially restricted lower Atokan fluvial deltaics
• displaced by shallow marine siliciclastics
• followed by pervasive carbonate deposition in the
  western Permian Basin.

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AtokanSiliciclastics
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Lower Atokan Siliciclastics

• Sequence boundary marks Morrowan to Atokan
  transition.
• The lower Atokan is characterized by lowstand
  deposition of alluvial and fluvial incised valley
  deposits (Eddy Co. NM and Cottle Co. TX),
  fan-delta deposits in the Palo Duro Basin and
  Upton Co. TX and basin-floor fans in Midland and
  Andrews Counties

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Middle Atokan Siliciclastics

• As mid-Atokan sea level rose, tectonic uplift of
  the Pedernal area decreased and marginal marine
  to open marine deltaic to shelfal siliciclastic
  sedimentation began to dominate.
• Shoreline-parallel, barrier bar to shelf ridge
  sedimentation dominated in the Northwest Shelf
  area of New Mexico with a sediment source still
  largely from the northwest.
• Extensive deposition of shale units (e.g.
  Smithwick Fm.) occurred during middle to upper
  Atokan time as the progradational front to the
  Atokan siliciclastics migrating westward from the
  Fort Worth Basin.

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PERMIAN BASINDATA
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• Lowstand sandstone unit in the Type log for
  the Atokan succession on the Northwest Shelf

Porosity in the reservoir zone ranges from 9-12
Empire Field, Eddy Co. N.M.
(after James, 1985)
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Middle AtokanTransgressive Siliciclastics
Shelf Ridges Or Barrier Island Arcs
(after James, 1985)
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Smithwick Formation

• Regionally extensive
• Equivalents shales in the Delaware and Midland
  Basin
• High organic carbon content (7.5 TOC)
• Interfingers with both siliciclastic and
  carbonate units
• Barnett-style shale gas play??

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Key Points on AtokanSiliciclastic Deposition

• Dominantly eustatic control of facies packaging
  and distribution minor tectonic input
• Ozona Arch source area for the Upton and Midland
  Co. fan-delta and basin floor fans
• Middle to late Atokan transgressive shore
  parallel sandstone bodies have good reservoir
  quality and a distribution that is relatively
  easy to predict using sequence stratigraphy

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AtokanCarbonates
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Atokan Carbonate Deposition

• Atokan age carbonates in the Permian Basin are
  lateral equivalents to the Upper Marble Falls Fm.
  on the Eastern Shelf. The Eastern shelf
  succession provides both subsurface and surface
  analogues for the Permian Basin
• Overall, Atokan carbonate deposition occurred
  over a much larger area in the Permian Basin than
  previously documented. Deposition of the
  carbonate occurred on low-angle ramps which
  developed into more platform-like geometries
  through time
• Shallow-water Donezella algal bioherms and
  oolitic bioclastic grainstones are intrinsically
  the most favorable reservoir facies. However,
  reservoir intervals are not linked to a specific
  facies or exposure surface

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PERMIAN BASINDATA
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Chapman Deep Field(Reeves Co., TX)
(after Mazzulo, 1981)
Transgressive surface
Flooding surface
Sequence boundary
Total Atokan thickness 670-1200 ft/205-307 m
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Chapman Deep Field

• Primary porosity largely occluded
• Secondary development of porosity during burial
  diagenesis via leaching
• Extensive microfracture network

(after Mazzulo, 1981)
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Upper Marble Falls Fm.

• Bioherms tend to be dominated by Komia and
  Chaetetes
• Bioherm dimensions equivalent to those of the
  Lower Marble Falls Fm.
• Average 10 porosity and 2 to 6 mD permeability
  in mound/bioherms and shoals

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Atokan Carbonate Distribution

• The Upper Marble Falls Fm. is present on the
  Eastern Shelf within the Permian Basin and
  connects with a thick succession of carbonates
  nucleated on the Devils River Uplift in Val Verde
  and Edwards Co.
• This carbonate dominated region links up across
  the Central Basin Platform and into the northern
  Delaware Basin

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Atokan Paleogeography
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Desmoinesian
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Regional Sedimentation Patterns

• Carbonate production dominated during the
  Desmoinesian the Permian Basin
• Siliciclastic sediments are restricted to the
  Eastern Shelf and extreme northwest of the
  Permian Basin.

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DesmoinesianSiliciclastics
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Desmoinesian Siliciclastics

• Cyclic sedimentation between siliciclastics and
  carbonates on the Eastern Shelf
• Delta front facies present in the Permian Basin
  coarser facies (e.g. alluvial channels) generally
  to the east
• Areally minor basin center shales

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Eastern Shelf Succession
(after Cleaves, 2000)

• The Dobbs Valley and Buck Creek depositional
  episodes prograded the farthest west

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Deltaic Front Facies

• Eastern Shelf
• (e.g. Coke and Nolan Counties)

Buck Creek equivalent?
Tuscola Field (Taylor Co.)
110ft/33.5m
(after Shannon and Dahl, 1971)
Lowstand channels superimposed on a highstand
delta
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Reservoir Quality and Diagenesis

• Bbar crest laminated sandstones are the main
  producing interval. Secondary production comes
  from delta front channels
• Porosity 0-15.2 (mean 5.3)
• Permeability 0-387mD
• Extensive cementation - quartz followed by
  calcite total occlution
• Dissolution of calcite cement and framework
  grains yielded present porosity of 15

2.25in
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DesmoinesianCarbonates
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Desmoinesian Carbonate Deposition

• Pervasive carbonate deposition in the Permian
  Basin
• Early Desmoinesian
• relatively uniform thickness and wireline log
  signature
• ramp settings
• Middle to Late Desmoinesian
• Large thickness differences
• Multitude of depositional settings ramps, patch
  reefs, shelf-margins, rimmed shelves
• Shallow-water phylloid algal bioherms, Chaetetes
  reefs and bioclastic packstone/grainstones are
  the most favorable reservoir facies. Phylloid
  algae tend to dominate the bioherm community
  during the Desmoinesian.

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Lower Desmoinesian Carbonates
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(After Waite, 1993)
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Southwest Andrews Field Area (Andrews Co.)
(after Saller et al. 1999)
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(after Saller et al. 1999)
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(after Saller et al. 1999)
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Middle toUpper Desmoinesian Carbonates
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Subsidence

• Subsidence of the Midland Basin began in the
  Middle to Late Desmoinesian
• Profound affect on the geometry of the carbonate
  depositional systems
• True shelf margins formed on the Eastern shelf
  and along the southern margin of the Horseshoe
  Atoll
• Overall, carbonates were aggradational in
  response to increased accommodation

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Late Desmoinesian

• Shelf-margin becomes geographically fixed

(after Mazzulo, 1989)
Nena Lucia Field (Nolan Co.)
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Reservoir Quality in Desmoinesian Carbonates

• Function of facies type and exposure related
  diagenesis
• Best reservoir intervals lie below the sequence
  boundary between the Desmoinesian and Missourian
  (Strawn Fm.-Canyon Fm.). A second older regional
  exposure event also caps a reservoir interval
• Porous zones range from 1000ft/300m to several
  mi/km across

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Southwest Andrews Field Area (Andrews Co.)
Lateral reservoir quality beneath the sequence
boundary and associated exposure surface
(after Saller et al. 1999)
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Deep Burial Diagenesis and Fracturing

• Reservoir quality in the Val Verde Desmoinesian
  (Strawn Fm.) succession is tied to facies type,
  extent of subaerial exposure and is overprinted
  by compression induced fracturing following by
  migration of connate high-temperature oil-bearing
  fluids

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South Branch Field (Terrell Co., TX)
Moldic porosity largely associated with phylloid
algal packstones linked by microfractures
Exposure related brecciation and pseudo-breccias
(after Newell et al. 2003)
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Pakenham Field (Terrell Co., TX)
Stacked thrusted and backthrusted reservoir
intervals
Lateral facies changes
Structural complexity increases with depth
(after Montgomery, 1996)
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Key Points on DesmoinesianCarbonate Deposition

• Eustatic sea-level falls are vital for reservoir
  development
• Desmoinesian carbonates are present on the
  Central Basin Platform and in the Val Verde Basin
  (i.e. Central Basin Platform was not uplifted yet
  and the Val Verde Basin had not truly formed)
• Multiple play types are present
• Subsidence of the Midland Basin began in the
  middle to late Desmoinesian with a eastern
  flexural hinge line corresponding to the Fort
  Chadbourne Fault Zone

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Desmoinesian Paleogeography
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MissourianVirgilian
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MissourianVirgilian

• Introduction to core workshop
• SACROC 37_11 Core
• Canyon and Cisco Formations
• Icehouse System oscillations (65-460ft)
  (20-140m)
• 700 ft (310m) thick reservoir column
• lower-mid Canyon
• open-shelf subtidal (low diagenetic alteration)
• upper-Canyon to lower Cisco
• high energy shoals (high diagenetic alteration)
• Lowstand slope wedge debris aprons

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Horseshoe Atoll?
(after Dutton, 2004)
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SACROC
(after Dutton, 2004)
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SACROC17-5

• WLL and Facies for 17-5
• Crestal Position
• Subtidal cycles capped by deepwater cycles
• Low Gr throughout

(after Dutton, 2004)