Integrated Reservoir Solutions Sedimentology and Stratigraphy of Lower Smackover Tight Oil Carbonates: Key to Predictive Understanding of Reservoir Quality and Distribution Roger J. Barnaby 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
Lower Smackover Depositional Setting Blakey 2007
Gulf Coast Jurassic Stratigraphy
Lower Smackover Core: Overview GR Cycles Facies Lith XRD Vis Por CMS 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 Facies Skel - Pel PS Skel - Pel WS Laminated MS Siliciclastic Siltstone XRD Mineralogy Calcite Illite Quartz Anhydrite
Lower Smackover: Ternary Diagram Clay (Vol %) Lithology ranges from clean limestone to argillaceous silt Illite dominant clay mineral Calcite+ Dolomite (Vol %) 0 10 20 30 40 50 60 70 80 90 100 Qz+K- Feld+Plag (Vol %)
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
Microbial Laminite Facies 0.5 mm 1 mm 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!
Skeletal-Peloid Packstone CYCLES FACIES LITH WL OBMI STATIC GR RES 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 XRD Vis Por CMS 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 Facies Skel - Pel PS Skel - Pel WS Laminated MS Siliciclastic Siltstone XRD Mineralogy Calcite Illite Quartz Anhydrite
Lower Smackover Cyclicity & Stratigraphy GR Cycles Facies Lith XRD Vis Por CMS 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 Facies Skel - Pel PS Skel - Pel WS Laminated MS Siliciclastic Siltstone XRD Mineralogy Calcite Illite Quartz Anhydrite
Lower Smackover Cyclicity & Stratigraphy CYCLES FACIES LITH WL OBMI STATIC GR RES 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 Facies Skel - Pel PS Skel - Pel WS Laminated MS Argillaceous Nodular MS Siliciclastic Siltstone
Lower Smackover Cyclicity & Stratigraphy CYCLES FACIES LITH WL OBMI STATIC GR RES In upper interval, cycles consist of high GR argillaceous siltstone that pass upward into low GR skeletalpeloid PS Facies Skel - Pel PS Skel - Pel WS Laminated MS Argillaceous Nodular MS Siliciclastic Siltstone
Lower Smackover Sequence Stratigraphy 100 ft 200 ft 300 ft 400 ft 500 ft Cycle-Sequence Stratigraphy: High-Resolution Correlation
PERMEABILITY (Kair) Lower Smackover Reservoir Quality 100 CMS PLUG DATA 10 1 0.1 0.01 0.001 0.0001 0 2 4 6 8 10 POROSITY Upward increase in visual and measured porosity due to increasing proportions of skel-pel PS Depositional texture thus represents primary control on reservoir quality
Lower Smackover Reservoir Quality
Lower Smackover Reservoir Quality 0.5 mm 0.2 mm
Lower Smackover Fractures
Lower Smackover Conclusions 1. Vertical stacking of cycles and facies defines intermediateand 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