Eagleford Shale Exploration Models: Depositional Controls on Reservoir Properties*
Kevin Corbett1
Search and Discovery Article #10242 (2010)
Posted May 31, 2010
*Adapted from oral presentation at AAPG Annual Convention, and Exhibition, Denver, Colorado, June 7-10, 2009, and presentation at the Dallas SPWLA chapter,
January 14, 2010
1
Wrangler Resources, LLC, Denver, CO (kcorbett@frii.com)
Abstract
Exploration in the Eagleford Shale follows on recognition that a large percentage of the hydrocarbons generated never migrated. The
Eagleford has long been seen as a major petroleum source, principally for the Austin Chalk, but also for oil in the underlying Buda, and in
shallower Cretaceous and Tertiary horizons. Previous work has focused primarily on source rock character and documenting source potential.
Important now is understanding the Eagleford in a reservoir context and documenting depositional, diagenetic, and structural controls on
hydrocarbon saturation, permeability, lateral and vertical variability to optimize leasing, horizontal bore location, and completion techniques.
Lower Cretaceous basin geometry exerted a primary control on Eagleford Shale deposition, creating local depocenters where primary organic
content is higher, controlling downslope current transport, thereby producing areas of ponded density-current deposits, bypassed margins, and
focusing the location of more distal turbidite fans. In addition, Eagleford depocenter geometry exerted fundamental control on later migration
through fault reactivation, which established pathways and barriers to up-dip migration.
This study focuses on an area extending from LaSalle County in the southwest through Atascosa, Wilson, and Gonzales to Fayette County on
the northeast and down-dip through Webb, McMullen, Live Oak, Karnes, and Dewitt counties. Two fundamental plays are found in this
region, separated by the Stuart City Edwards reef trend. Up-dip of the reef margin, the Eagleford is normally pressured, primarily an oil
reservoir, characterized by significant lateral variability in organic-rich shale abundance and reservoir quality related to reef margin controlled
depocenters. Down-dip of the reef margin the Eagleford is modestly to strongly over-pressured, primarily a gas reservoir, and characterized
by lateral reservoir variability and primary permeability controlled by the location of distal turbidite deposition. Reactivation of faults
underlying the Stuart City trend produced barriers to up-dip migration and areas of focused gas accumulation. Corridors between reactivated
faults focused oil migration and produced significant variability in oil saturation within the up-dip play. Mapping basic rock properties on
well logs has allowed high-grading of Eagleford reservoir properties and suggests the potential to define seismically optimal well locations.
Copyright © AAPG. Serial rights given by author. For all other rights contact author directly.
References
Condon, S.M., and T.S. Dyman, 2006, 2003 geologic assessment of undiscovered conventional oil and gas resources in the Upper Cretaceous
Navarro and Taylor Groups, Western Gulf Province, Texas: U.S. Geological Survey Digital Data Series DDS–69–H, Chapter 2, 42 p.
(http://pubs.usgs.gov/dds/dds-069/dds-069-h/) (accessed May 27, 2010)
Corbett, K.P., D.R. Van Alstine, and J.D. Edman, 1997, Stratigraphic controls on fracture distribution in the Austin Chalk: AAPG Hedberg
Research Conference, Reservoir Scale Deformation - Characterization and Prediction, June 22-28, 1997, Bryce, Utah (also Applied
Paleomagnetics,Inc. --http://www.appliedpaleomagnetics.com/Articles/Pdf/1997Corbett.pdf) (accessed May 27, 2010).
Grabowski, G. J., Jr., 1995, Organic-rich chalks and calcareous mudstones of the Upper Cretaceous Austin Chalk and Eagleford Formation,
south-central Texas, U.S.A., in B. Katz, ed., Petroleum source rocks: New York, Springer-Verlag, p. 209–234.
Eagleford Shale
Exploration Models:
Depositional Controls
on Reservoir Properties
Kevin Corbett – Wrangler Resources, LLC
1801 Broadway, Suite 910
Denver, CO 80202
303-292-4110
wrangler resources, llc
PRESENTATION OVERVIEW
9 General Eagleford Characteristics
9 Play Activity
¾ Geographic extent of drilling - Reported production tests/rates
9 Regional Geologic Setting - S. Texas & Karnes Trough
9 Study Area – Wilson, Karnes, Gonzales & Dewitt Cos.
¾ Structural controls on deposition
¾ Stratigraphic variation with structure
9 Summary & Conclusions
wrangler resources, llc
EAGLEFORD SHALE PLAY
9 Source Rock for Austin Chalk & Buda Lime production
9 Structural & Strat Controls on Eagleford Source
Quality, Migration/Trapping, Reservoir Quality
9 Person – Dubose Edwards Shelf Edge Divides Oil &
Gas Plays
¾ Down-Dip Gas Play – expanded ‘un-deformed” AustinEagleford
¾ Up-Dip Oil Play – many similarities to Bakken
9 Karnes Trough - local depo-center of thick, organicrich Eagleford Shale
¾ Sediment trap for shelf-derived Eagleford “middle” siltstone
¾ Fault-controlled graben system with expected higher natural
fracture intensity
wrangler resources, llc
REFERENCE MAP EAGLEFORD
FOCUS
FOCUS AREA
AREA
LaSalle
LaSalle to
to Brazos
Brazos Counties
Counties
wrangler resources, llc
UPPER CRETACEOUS STRATIGRAPHY
From: Condon & Dyman, 2006: USGS DDS-69-H
wrangler resources, llc
CHRONOSTRATIGRAPHY
UPPER CRETACEOUS
9Lower Eagleford
Onlaps Underlying
Buda Ls
9Upper Eagleford
Max Flood Shale
TOP AUSTIN
TOP EAGLEFORD
TOP BUDA
9Austin Chalk
Thickens Basinward
& Grabowski
Identifies a Lower
Distal Member
From: Grabowski, 1995
wrangler resources, llc
EAGLEFORD DRILLING ACTIVITY
965 Wells – 6/05 through 5/09
¾11 Edwards Down-Dip Trend
¾32 Greater Grimes Field
¾22 Karnes Trough Up & Down
917 New Drills W/Prod.Rpt.
934 Oil Play – 31 Gas Play
9170 – 345 BOPD IP Grimes Oil
93.8 – 8.3 MMCF/D Edwards
96.5 – 12.1 MMCFE/D Karnes Tr.
Strat Section
S. Texas
wrangler resources, llc
EAGLEFORD DRILLING ACTIVITY
APACHE
I
SE
GIESENSCHLAG +
170 – 345 BOPD
ne
Li
SEQUOIA
SEQUOIA ACREAGE
ACREAGE
Drilled
Drilled &
& Completed
Completed
Drilling
Drilling or
or Permitted
Permitted
Ex
xo
BURLINGTON
05
40
EOG
MILTON UNIT 1H 350BOPDn BURLINGTON
Li
-340
A-340
ne A
Restricted Rate
25
1H,
1H, 2, 3H, 4, 10H
59
HARPER 1H,
1H, 2H, 3H, 4H, 8H
LYSSY 11,, 2H,
2H, 3, 6H
BURLINGTON
HOOKS
Tested No Info
Released
do
re
La
DAN HUGHES
Li
DARLENE 1H, 2H, 3H
HALL 2
Kaspzyk-Jendruch 1H
Kaspzyk
Kaspzyk-Jendruch
ne
LR
MURPHY
PIONEER
PIONEER
SUGARLOAF
SUGARLOAF ++
DRESSER A-179
AA-179
FREDERICHS
FREDERICHS 1H
1H
HANDY
HANDY 1H
1H
55 -12
-12 MMCFE/D
MMCFE/D
PETROHAWK
DORA MARTIN
STS, DONNELL HENDERSON,
BROWN TRUST
xo
Ex
n
Li
ne
3
28
WEBER
TEXAS
TEXAS CRUDE
CRUDE MIGURA
MIGURA
KENNEDY
KENNEDY
0.5
0.5 –– 1.5
1.5 MMCFE/D
MMCFE/D
Easley
-1
28
Easley 2828-1
61
3.8MMCF/D
395BC/D
4.5MMCF/D
225BC/D
4.3 – 9.1 MMCF/D
0 – 260 BC/D
8.3 – 13.2 MMCF/D
0 – 50 BC/D
B
38
BURLINGTON
BURLINGTON
wrangler resources, llc
SOUTH TEXAS STRAT SECTION
Lwr Austin TOC Avg 3.7%
Eagleford TOC Avg 3.7%
From: Grabowski, 1995
wrangler resources, llc
Eagleford Shale Drilling Results
+D\QHVYLOOHDQG(DJOHIRUG7KH*HRORJLF
6LJQDWXUHRI&RUH5RFN
E a g l e f o r d Shale: HK DORA MARTIN #1H
KARNES TROUGH AREA
PILGRIM X-SEC
C
BELL SAMPLE NO.1
KARNES X-SEC
HENRY KORTH NO.1
A
D
SEISMIC
B
wrangler resources, llc
EAGLEFORD TYPE LOG
HENRY KORTH NO.1
Anacacho
Austin Chalk
9Top Eagleford picked
on SP & Resistivity
9High GR doesn’t
correlate with SP & ILD
9Lower Austin of
Grabowski SP-GR “Gap”
Eagleford
“Lower Austin”
ES - silt
9Oil Saturation in core
correlates with >40 ohm
9“Middle” silt has drill
break & gas shows
Buda
wrangler resources, llc
EAGLEFORD CORE BELL SAMPLE NO.1
wrangler resources, llc
EAGLEFORD GROSS ISOPACH
PILGRIM X-SEC
C
BELL SAMPLE NO.1
KARNES X-SEC
D
SEISMIC
HENRY KORTH NO.1 B
A
wrangler resources, llc
EAGLEFORD NET ISOPACH
PILGRIM X-SEC
C
BELL SAMPLE NO.1
KARNES X-SEC
D
SEISMIC
HENRY KORTH NO.1 B
A
wrangler resources, llc
STRAT-SECTION KARNES TROUGH
A
B
wrangler resources, llc
STRAT-SECTION PILGRIM AREA
C
D
wrangler resources, llc
AUSTIN-EAGLEFORD FRACS VS DEPTH
From: Corbett, Van Alstine & Edman, 1997.
wrangler resources, llc
AUSTIN-EAGLEFORD
MATURATION-MIGRATION-TRAPPING
Austin Chalk compacted early – lost substantially all matrix porosity & permeability
Barrier to fluid migration
Eagleford Shale enters oil maturity at 6000’ burial – peak oil 8000’-9000’
Excess fluid pressure with maturity
Natural “hydrofracturing” at Austin-Eagleford contact
Faults and others barriers to migration bank oil down-dip
wrangler resources, llc
CULPEPPER A-H1 RATE-TIME
wrangler resources, llc
AUSTIN RE-WORK
INCREMENTAL PRODUCTION
wrangler resources, llc
EAGLEFORD OILS FIRST SHOT FIELD
9Family 1A Oil
– Less Mature,
Formed Where Found
9Family 1B Oil
– Maturity Exceeds
Present Day DOB, Migrated
From: Corbett, Van Alstine & Edman, 1987.
wrangler resources, llc
EAGLEFORD PLAY DISTRIBUTION
Ea
or
f
e
gl
d
ay
l
lP
i
O
Ea
d
r
o
ef
l
g
s
a
G
ay
l
P
wrangler resources, llc
SUMMARY
9 Person-Dubose Edwards shelf edge breaks the
Eagleford Play into an up-dip oil play and a down-dip
gas play
¾ Controls migration with faults as barriers
¾ Created the Karnes Trough depocenter – thicker section,
restricted circulation, trapped “middle” siltstone
9 Austin-Eagleford contact is gradational and thus a
continuous system for reservoir purposes
9 >40 Ohm deep resistivity correlates well with oil
saturated core & shows
9 Trapping by up-dip pinchout & fault barriers
wrangler resources, llc