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