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Integrated Reservoir Solutions
Roger J. Barnaby
Sedimentology and Stratigraphy of Lower Smackover Tight Oil Carbonates: Key to Predictive Understanding of Reservoir
Quality and Distribution
Presented at 2013 AAPG Black Shale Core Workshop
Lower Smackover Summary
• Natural fractures in the Lower Smackover provide inadequate storage capacity for commercial success
• Key geologic uncertainty is matrix porosity, which reflects depositional and stratigraphic controls
Blakey 2007
Lower Smackover Depositional Setting
Gulf Coast Jurassic Stratigraphy
Lower Smackover Core: Overview
GR Cycles Facies Lith
Skel - Pel PS
Skel - Pel WS
Laminated MS
Siliciclastic Siltstone
Facies
Vis Por
• 360 ft “Brown Dense” recovered
• Interbedded limestone & argillaceous
siltstone
• Limestones low GR, siltstones high GR
• GR log displays cyclic interbedding of
the two lithologies
Calcite
Illite
Quartz
Anhydrite
XRD Mineralogy
XRD CMS Por
Lower Smackover: Ternary Diagram
0 10 20 30 40 50 60 70 80 90 100
Clay
(Vol %)
Calcite+
Dolomite
(Vol %)
Qz+K-
Feld+Plag
(Vol %)
Lithology ranges from
clean limestone to
argillaceous silt
Illite dominant clay
mineral
Lower Smackover Sedimentology CYCLES FACIES LITH WL OBMI STATIC
GR RES
Microbial Laminite Facies
Laminated lime MS intercalated with thin organic partings & silt-rich stringers
Wavy-, planar-, and low angle ripple-lamination, burrow-disrupted lamination, small synsedimentary folds & faults
1 mm0.5 mm
Microbial Laminite Facies
Interpreted as sticky microbial mats that trapped & bound carbonate mud
Organic content & preserved laminations suggest dysaerobic, below SWB
Outer ramp, estimated water depths 100-300 ft
Source rock and intra-reservoir permeability barriers!
GR RES
CYCLES FACIES LITH WL OBMI STATIC
Skeletal-Peloid Packstone
Reservoir!
Lower Smackover Facies: Skel-Pel PS
Skeletal, peloids, quartz silt
Winnowing of lime mud above SWB, mid-ramp
Normal marine – skeletal grains, pellets, bioturbation
< 100 ft water depth
Argillaceous Quartz Siltstone Facies
Interbedded ductile beds limit fracture height!
Lower Smackover Depositional Model
Estimated maximum water depths 150-300 ft
Below SWB and bioturbation
Lower Smackover Cyclicity & Stratigraphy
GR Cycles Facies Lith
Skel - Pel PS
Skel - Pel WS
Laminated MS
Siliciclastic Siltstone
Facies
Vis Por
• Upward increase in SiO2 records increasing
continental influx during long-term prograd.
• Carbonates: Distal laminites in lower interval
pass upward into proximal skel-pel PS
• Lithology & facies reflect SL:
• -TST/ early HST - less SiO2 influx, more
CO3 on flooded shelf, distal laminite facies
• -Late HST/LST increased influx of SiO2,
more proximal skel-pel PS
Calcite
Illite
Quartz
Anhydrite
XRD Mineralogy
XRD CMS Por
Lower Smackover Cyclicity & Stratigraphy
GR Cycles Facies Lith
Skel - Pel PS
Skel - Pel WS
Laminated MS
Siliciclastic Siltstone
Facies
Vis Por
• Several scales of cyclity defined by
interbedded siliciclastic & carbonate facies
• High frequency, > 90 cyclic repetitions (2-
10 ft thick) of SiO2 & CO3
• Intermediate frequency: composite cycles
• Low frequency: long-term progradation
Calcite
Illite
Quartz
Anhydrite
XRD Mineralogy
XRD CMS Por
Lower Smackover Cyclicity & Stratigraphy
Skel - Pel PS
Skel - Pel WS
Laminated MS
Argillaceous Nodular MS
Siliciclastic Siltstone
Facies
GR RES
CYCLES FACIES LITH WL OBMI STATIC
• In lower interval, cycles consist of high GR
argillaceous siltstone that pass upward
into low GR microbial laminated micrite.
• Laminated micrites may grade into
overlying skel-pel PS
Lower Smackover Cyclicity & Stratigraphy
GR RES
CYCLES FACIES LITH WL OBMI STATIC
Skel - Pel PS
Skel - Pel WS
Laminated MS
Argillaceous Nodular MS
Siliciclastic Siltstone
Facies
• In upper interval, cycles consist of
high GR argillaceous siltstone that
pass upward into low GR skeletal-
peloid PS
Lower Smackover Sequence Stratigraphy
Cycle-Sequence Stratigraphy: High-Resolution Correlation
100 ft
200 ft
300 ft
400 ft
500 ft
• Upward increase in visual and measured
porosity due to increasing proportions of
skel-pel PS
• Depositional texture thus represents
primary control on reservoir quality
0.0001
0.001
0.01
0.1
1
10
100
0 2 4 6 8 10
PER
MEA
BIL
ITY
(K
air)
POROSITY
CMS PLUG DATA
Lower Smackover Reservoir Quality
Lower Smackover Reservoir Quality
0.5 mm 0.2 mm
Lower Smackover Reservoir Quality
Lower Smackover Fractures
Lower Smackover Conclusions
1. Vertical stacking of cycles and facies defines intermediate- and long-term depositional sequences for correlation, mapping, and modeling
2. Insufficient natural fracture storage for commercial success
3. Matrix storage is key geologic uncertainty
4. Visible porosity confined to proximal grain-rich skel-pel PS
5. Depositional and stratigraphic processes exert the primary control on reservoir quality and distribution
