Characterization of the Missisissippian Osage Chat in South-Central Kansas

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Characterization of the Missisissippian Osage
Chat in South-Central Kansas

• Alan P. Byrnes,
• Willard J. Guy, W. Lynn Watney
• Kansas Geological Survey

2
Distribution of Mississippian chat fields in
Kansas
Low resitivity pays stratigraphic traps
cum. Gas 2.4 TCF cum. Oil 280 MM bbls.
Potential for reexploration and IOR using
appropriate recovery technologies
(from Montgomery et al., 1998)
3
Overview

• Regional geology and depositional environment
  controls
• Lithofacies and depositional sequences
• Tectonic controls
• Reservoir petrophysical properties
• Porosity and Permeability
• Capillary pressure, Relative Permeability,
  Electrical
• Wireline log response

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Stratigraphic section of upper Devonian,
Mississippian, and Pennsylvanian Systems

• Cowley Formation accumulated on shelf margin as
  an interval equivalent to succession of
  formations deposited on the shelf in Osage and
  Meramec Series

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Plate Tectonics During Carboniferous
335 Ma
310 Ma
(after Zeigler, 1989)
Proto-Anadarko Basin converging plates
6
3rd and 4th Order Cycles During Mississippian
7
Paleogeographic map during Osage
(after Lane, H.R., and De Keyser, T.L., 1980 )
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Mississppian Subcrop
(Gerlach, 1998)
http//crude2.kgs.ukans.edu/DPA/Plays/ProdMaps/mis
s_sub_gas.html
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Major Depositional Characteristics

• Mississippian siliceous sponge-microbe
  communities
• low relief biostromes and bioherms surrounded by
  mudstone
• accumulation of sponge spicule-rich
  wacke-packstones
• Conditions favorable for accumulation may have
  been created in response to basement block
  movement
• T-R cycles on a shelf to shelf margin setting
  resulted in a series of shallowing cycles
• Ranging upward from sponge spicule-poor
  argillaceous mudstone to sponge spicule rich
  wacke-packstones which were overlain by
  bioclastic wacke-grainstone shelf deposits and
  terminated by an exposure surface
• Sponge spicule content may increase upwards with
  increasing cycle thickness
• Soon after burial these were silicified

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Depositional Settings for Siliceous
Sponge-Microbe Reef Mounds

• A) Differentiated carbonate shelf
• B) Reef-rimmed shelf
• C) Carbonate ramp or nonrimmed shelf

(after Brunton and Dixon, 1994)
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(after Brunton and Dixon, 1994)
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Major Lithofacies

• 1 Chert Conglomerate w/Clay
• 2 Autoclastic Chert w/Clay
• 3 Autoclastic Chert
• 4 Nodular to Bedded Chert
• 5 Cherty Dolomite Mudstone
• 6 Argillaceous Dolomite Mudstone
• 7 Bioclastic Crinoidal Wackestone-Grainstone
• 8 Sucrosic Dolomite
• 9 Shale

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BVW
porosity
Conglomerate
Spivey-Grabs Field General Atlantic Tjaden A-1 WIW
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1. Chert conglomerate

• General Atlantic, Tjaden 1A1 WIW 1, 4323.5 ft,
  chert conglomerate containing clasts of
  oil-stained chat and chert in silty, clay matrix
  with smaller chert clasts. Scale bar is 2 cm.
  Thin section photomicrograph, 4322.5 ft, from
  inside chat pebble containing abundant molds of
  sponge spicule and small vugs filled by blue
  epoxy. Porous microcrystalline quartz and
  microcrystalline calcite (stained with
  alizarin-red) comprise matrix, replaced by
  patches of megaquartz (white). Irregular vugs
  cross cut other fabrics. Scale bar is 0.1 mm.

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2. Autoclastic chert with clay

• General Atlantic, Tjaden 1A1 WIW 1, 4337 ft,
  autoclastic chert breccia with clay infiltration
  below arrow. Interpenetrating clasts of brown
  porous chat. Thin section photomicrograph from
  4398 ft. contains autoclasts lined by clay and
  brown microcrystalline calcite. Abundant
  microporosity, molds, and vugs in spiculitic
  microcrystalline chert (chat). Scale bar is 0.1
  mm. Plane polarized light and blue epoxy
  impregnation

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3. Autoclastic chert
General Atlantic, Tjaden 1A1 WIW 1, 4346 ft,
autoclastic chert breccia with mottled oil
staining and fractures. Scale is 2 cm. Upper
photomicrographs, 4331 ft, shelter porosity.
Lower, 4331.5 ft, boundary between
interpenetrating clasts of highly porous chat.
Boundaries defined by dirty clay rim. Interior
of clasts contain varying amounts of
microcrystalline quartz and associated fine vuggy
and moldic porosity. Scale bars are 0.1 mm. Plane
polarized light and blue epoxy impregnation.
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4. Nodular-bedded chert
General Atlantic, Tjaden 1A1 WIW 1, 4379 ft,
nodules of chat in overpacked fabric with
interpenetrating clasts. Variable brown oil
staining identify separate clasts and associated
relative differences in microporosity. Individual
clasts show variations in staining along
discontinuous fracturing. Scale is 2 cm.
Photomicrograph from 4379.5 ft from within a chat
nodule containing micro-, moldic, and vuggy
porosity. Some micritic calcite preserved
stained with alizarin-red. Scale bar is 0.1 mm.
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5. Cherty dolomite mudstone6. Argillaceous
dolomite mudstone
General Atlantic, Tjaden 1A1 WIW 1, left photo
showing gray dolomite mudstone with white chert
nodules. Lower nodule is stained with oil due to
presence of microporosity. Photo to right is
another example of a cherty, argillaceous
dolomite mudstone. It contains burrows, wavy, and
lenticular bedding suggesting moderate
bioturbation. White rounded and small
lenticular-shaped chert nodules suggest selective
silicification of burrows. Scale bars are 2 cm.
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7. Bioclastic wacke/grainstone

• General Atlantic, Tjaden 1A1 WIW 1, 4347 ft,
  showing a contact (at arrow head) between
  encrinitic grainstone (lower right) and
  autoclastic chert. Top of encrinite is solution
  microkarst. Solution cavities are deep, cutting
  through approximately 0.5 m of core. Contact is
  also boundary of cycle 2. Encrinite is tightly
  cemented by calcite stained here with
  alizarin-red. Scale is 2 cm. Photomicrograph
  below the rock slab from 4341 ft from encrinite
  capping the thin cycle 3. Alizarin-red stain
  helps to distinguish the slightly darker and
  cloudy crinoid ossicle from the syntaxial calcite
  overgrowth cement. Unstained patches of replacive
  microquartz with accompanying microporosity and
  vugs also shown. Blue epoxy also shows a small
  amount of interparticle porosity. Scale is 0.1
  mm. Photographed in plane polarized light.

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SEM Robbins 1-36 - 4856 ft
10 microns
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Post-deposition

• During inter- and post- Mississippian subaerial
  exposure facies underwent further diagenesis
• sponge spicule dissolution
• vuggy porosity development in moldic rich rocks
• Autobrecciation
• Areas of increased diagenesis can be correlated
  with basement lineaments
• Recurrent movement
• Create topography for exposure
• Local preservation in lower relief blocks
• Bounding fault seals
• Meteoric water influx, or the range of the mixing
  zone controlling diagenesis
• Limited in depth below the exposure surface
• Limited in depth downdip into unaltered cherty
  Cowley Formation facies
• Combination of original accumulation, block fault
  movement, sponge spicule concentration, and
  possibly thickness of overlying bioclastic
  wacke-grainstones resulted in variable reservoir
  properties and the creation of pods of production
  separated by non-productive cherty dolomite
  mudstones.

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Mississippian Structure and Lineaments

• Structural contour map with oil production
  (Gerlach, 1978) http//crude2.kgs.ukans.edu/DPA/Pl
  ays/ProdMaps/miss_oil.html

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Bouguer gravity

• Bouger gravity overlain with structural contours
  of Precambrian map from Cole (1976). Blues
  represent lowest residuals and reds represent
  highest residual values displayed with apparent
  relief created by vertical illumination. Steeper
  gradients are indicated by darker shading. (after
  Kruger, 1997) http//crude2.kgs.ukans.edu/DPA/Play
  s/Grav/ksGravCole.html

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Total Magnetic Field Intensity

• Reduced-to-the-pole magnetic data displayed in
  similar way as gravity data http//crude2.kgs.ukan
  s.edu/DPA/Plays/Mag/coleMed.html. Map overlain
  with A and B lineaments and recognized
  basement faults and structural contours of
  Precambrian map from Cole (1976) (after Kruger,
  1997)

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Isopach map of Late Devonian-Early Mississippian
clastics
425 data points eastern 2/3rds of Kansas
Contour interval 50 ft.
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Isopach map of Mississippian Carbonates
Contour interval 50 ft.
contrasting accommodation to underlying clastics
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Isopach map of the Cowley Formation

• Lineaments A and B are shown delimiting
  northern edges of the formation. C.I.100 ft

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Isopach map of the chat

• C.I.10 ft. Lineaments A and B are shown
  delimiting southern edges of thick chat in the
  vicinity of the Pratt Anticline

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NW-SE Stratigraphic Cross Section
through Spivey-Grabs Field Vshale (Shale
Fraction) Mississippian Datum Top
Miss. Section Length 150 km (93 mi)
100 ft (15 m)
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Vsh NW-SE Structure cross section
Spivey-Grabs
500 ft
Lineament A
Section Length 150 km (93 mi)
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Spivey Grabs
Resistivity Index NW-SE Stratigraphic cross
section
Section Length 150 km (93 mi)
Lineament A
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Field examples
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Hardtner Field and Lineaments

• Hydrocarbon accumulations terminate at northern
  block boundaries
• (map still in development)

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Rhodes Field and Lineaments

• Lineaments define hydrocarbon accumulation and
  facies pinchout more than structure
• (map still in development)

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Nichols Field and Lineaments

• Chat thickness correlates with basement lineament
  fault defined blocks
• Hydrocarbon accumulations can occur along
  northern block boundaries
• (map still in development)

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Spivey-Grabs Field and Lineaments
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Spivey-Grabs Field and Lineaments
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Spivey-Grabs Field and Lineaments
pods of more productive, better developed chat

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Mississppian Subcrop
(Gerlach, 1998)
http//crude2.kgs.ukans.edu/DPA/Plays/ProdMaps/mis
s_sub_gas.html
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Reservoir Petrophysical Properties and Wireline
Log Response

• Each lithofacies exhibits a generally unique
  range of petrophysical properties

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Histogram of core porosities for four fields in
chat

• Bimodal distribution
• Low porosity - cherty dolomite mudstone facies
• High porosity - cherty facies
• Wireline logs exhibit similar bimodal distribution

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Permeability versus porosity for whole core

• Properties reflect both matrix and larger-scale
  properties including nontectonic fracturing
• Lower core plug trend
• ka10(0.072?a-1.51)
• Upper whole core trend
• ka10(0.067?a-0.53)

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Permeability versus porosity for core plugs

• Properties reflect only matrix properties
  excluding nontectonic fracturing
• Lower core plug trend ka10(0.072?a-1.51)
• Upper whole core trend
• ka10(0.067?a-0.53)

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Air permeability versus porosity for normalized
whole core and plugs for four chat fields
Glick

• Bates sucrosic dolomites (blue square) lie off
  chert trend

Spivey Grabs
46
Insitu Klinkenberg permeability versus principal
pore throat diameter

• Determined form mercury capillary pressure
• Samples lie off central trend as a function of
  mixed lithologies in plugs and variables like
  degree of vugginess
• Trend equation ki10(2.25PPTD-0.75)

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Capillary pressure curves Glick Field

• Autoclastic chert facies and clay
• All curves exhibit high irreducible saturations
  indicative of microporosity and consistent with
  wireline log measurements of high water
  saturation
• Purple diamond shows the curve for the green
  infilling clay

(after Duren , 1960)
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Imbibition water-oil relative permeability

• Autoclastic chert
• Gulf School Trust 4-4, Hardtner Field
• High critical water saturations are consistent
  with microporosity
• Limited saturation range of oil displacement may
  reflect dual porosity pore system though it gives
  appearance of intermediate oil-water wetness

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Relative gas permeability versus water saturation

• Saturations -Pc air-brine 33 psia, 55 feet
  above free water level
• Relative permeabilities decrease rapidly at
  saturations greater than 60
• Nodular cherts, dolomite mudstones, and
  bioclastic wackestones exhibit low krg,Sw

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Archie cementation exponent (m) versus porosity

• Chert conglomerate mavg2.590.27
• Autoclastic chert w/clay mavg2.36590.27
• Autoclastic chert mavg2.250.25
• Nodular chert mavg1.920.05
• Chert dolomite mudstone mavg1.970.11
• Bioclastic wacke-grainstone mavg1.770.05
• Trendline for m versus porosity
• m 0.014?a1.66

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Cementation exponent (m) versus depth

• General Atlantic WIW 1-A Tjaden,
  Spivey-Grabs Field
• Cementation exponents decrease with depth from
  surface to bioclastic wacke-grainstone interval
• Below bioclastic wacke-grainstone interval m in
  autoclastic cherts is high and decreases with
  depth again
• Patterns in m may reflect
• Systematic changes in pore type and/or
• Influence of paleo-perched water table

m increase with increasing vug and mold
content?
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PfEFFER Super-Pickett Plot
Cycle B
Cycle D
Cycle C
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Excellent Chat Reservoir
Chat
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Cowley Formation, Aetna Field
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Conclusions

• Mudstones to sponge spicule wacke-packestones
  were deposited in T-R cycles on a shelf to shelf
  margin setting in a series of shallowing upward
  cycles
• Early silicification, inter- and
  post-Mississippian subaerial exposure resulted
  in sponge spicule dissolution, vuggy porosity
  development in moldic rich rocks, and
  autobrecciation
• Areas of increased diagenesis can be correlated
  with basement lineaments and recurrent block
  movement
• Meteoric water influx, or the range of the mixing
  zone controlling diagenesis, appears to have been
  limited in depth below the exposure surface and
  in depth downdip into unaltered cherty Cowley
  Formation facies
• Combination of block fault movement, sponge
  spicule concentration, and possibly thickness of
  overlying bioclastic wacke-grainstones resulted
  in variable reservoir properties and the creation
  of pods of production separated by non-productive
  cherty dolomite mudstones
• These events also resulted in alteration of the
  depositional cycles to produce a series of
  lithofacies which each exhibit relatively unique
  petrophysical properties

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Conclusions

• Chert facies exhibit porosities ranging from
  25-50 and permeabilities gt5 md
• Cherty dolomite mudstones, argillaceous dolomite
  mudstones, and bioclastic wacke-packestones
  exhibit non-reservoir properties
• Reservoir production, simulation, and whole core
  data indicate fracturing can be present in chat
  reservoirs and can enhance permeability by up to
  an order of magnitude
• Capillary pressure data indicate the presence of
  microporosity and can explain high water
  saturations and low resistivity observed in
  wireline logs
• Relative permeabilities decrease rapidly for
  saturations gt 60 and may be influenced by dual
  pore systems
• Detailed modified Pickett plot analysis of logs
  reveals some of the chat character and can
  provide reliable indications of reservoir
  properties
• Models developed provide some additional insight
  into the chat of south-central Kansas and
  understanding the nature of controls on shallow
  shelf chert reservoir properties

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