Porosity partitioning in sedimentary cycles: implications for reservoir modeling
Gregor P. Eberli1), Langhorne B. Smith 2), Elena Morettini 3), Layaan Al-Kharusi1)
1) Comparative Sedimentology Laboratory, University of Miami2) New York State Museum, Albany, New York
3) Carbonate Development Team, Shell, Rijswijk, The Netherlands
1. Facies and diagenetic partitioning often divides sedimentary cycles (genetic units) into transgressive and regressive hemi-cycles with variable porosity and fracture behavior
2. Porosity partitioning follows stratigraphic cyclicity and can be implemented in reservoir modeling
Turn aroundTransgressive Hemicycle
Regressive Hemicycle
Pleistocene
HoloceneMud Bank
Pleistocene
Regressive part
Transgressive part
(Enos and Perkins, 1977)
ExposureExposure
ExposureExposure
Principle of Facies Partitioning
Different facies associations are produced during relative sea-level rise versus sea-level fall as a result of
•differences in direction and amount of energy
•differences in the fauna and flora•differences in the preservation potential
Principle of Diagenetic Partitioning
Diagenetic alteration varies with changing sea level as a result of
• changes in the fluid flow regime• changes in the sediment composition • changes in sedimentation rates
meteoric lenseRegression
meteoric dissolutio cementation
marine dissolution cementation
limestone dolomite
Transgression
marine cementatio dolomitization
Porosity Partitioning
Porosity partitioning occurs in• genetic unit• sets of genetic units • sequences and supersequences
Sheep Mountain Anticline: Mississippian Madison Formation
lithology
flooding surface
skeletal pack- grainstone
coarse grainstone
coralslaminatedstromatolites
skeletal pack- grainstone
marine shelf
Beach/tidal bars
shoal
middle shoreface
marine shelf
shoal
lagoonaltidal
environmentcycle
turnaround
transgressive hemicycle
regressive hemicycle
Genetic unit in the Mississippian Madison Formation
1mm
0.25mm
3rd
orde
r4t
h or
der
5th
orde
r
Limestone
DolomiteTransgressiveHemicycle
RegressiveHemicycle
Diagenetic Partitioning in thegenetic units of the MadisonFormation at Sheep Mountain
Sheep Mountain Low Angle Limb-C
M W P G
Hemicycles LithologyMechanical
Units
Mechanical Unit 4
Mechanical Unit 3
Mechanical Unit 5
Mechanical Unit 6
Mechanical Unit 2
Mechanical Unit 1Average Fracture
Spacing = 4cm
Average Fracture Spacing = 22cm
Average Fracture Spacing = 20cm
Average Fracture Spacing = 31cm
Average Fracture Spacing = 7cm
Are They Mechanical Boundaries?
0
20
40
60
80
100
120
1 2 3 4 5
No. o
f Fra
ctue
resTotal No. of Fractures
No. of Fractures Which Terminateat Boundary
Mechanical Boundary 1
Mechanical Boundary 2
Mechanical Boundary 3
Mechanical Boundary 4
Mechanical Boundary 5
High Resolution Sequence StratigraphyThe Method for Capturing porosity partitioning
Core analysisDetermination of genetic units
1) identification of facies trends on cores 2) separation into packages of transgressive/regressive hemicycles3) stacking of the genetic units into hierarchical higher cycles
Core to Log correlationCalibrate core to the logsCorrelation of calibrated logs to uncored wells
Model inputDetermination of appropriate cycle hierarchy for reservoir modeling
Rudist platform
Mid Ramp
Outer Ramp
Intrashelf Basin
Outcrops
Well locationsOil and gas fields
Sequence Stratigraphic Framework
Modified after Van Buchem et al. 2000submitted to AAPG;Van Buchem et al. 1996
Natih FieldFahud Field
FN 176 FN 3 NW 81 N7
organic-rich limestones
clayey marls
Bioclastic grainstones to packstones
Rudist floatstone/rudstone
Mudstone
Maximum flooding surface 3rd order
3rd order Sequence boundary
Decrease in accommodation space(regression)
Increase in accommodation space(trangression)
Facies Natih E
Regressive Deposits
a) ShoalCoarse-grained bioclastic grainstones and rudstones (orbitolina-rich grainstones and rudist bioclasts)
b) Shallow Shelf (with redistributed shoal sediments)Bioturbated, muddy pelletal wackestones
Transgressive Deposits
Pelletal Wackestones with clay and chert nodules
Morettini et al. submitted
SMALL SCALE CYCLE/GENETIC UNIT NATIH E FORMATION
Rudist buildup
Inter rudist/buildup
Inter rudist/buildup
Rudist buildup
Inter rudist/buildup
Rudist buildup
29.5
HRSS Cycles
Environmentof sedimentation Microfacies
K Φ mD %
4200
38
19
280
20.5
26.7
29.3
50
100
150
4th 3rd Lithostrat. Units
Lithology Facies, DiagenesisBedding Character and Clay
Proposed Mechanicaland Flow Units
D5
E1
E2
E3
E4a
E4b
E5rgpwm
Et1
Er2
Et2
Er3
Et3
Er4
Et4
Er5
Et5
Er6
Et6
mfs
mfs
mar
ine
met
eoric
mar
ine/
met
eoric
clay
Low flow
flooding surfaceargillaceous wackestone
Low flowmechanical boundary
Bioturbated wacke-packstonewith chert
submarine cementation
Homogeneousless porous flow unit“ductile” unit
Exposure surfaceWacke-packstone and interbedded coarse rudstones; thick bedsMarine diagenesisSparse dolomite intervals
Porous, homogeneousflow unit“ductile”unit with brittle layers
flooding zonewackestone with clay
Low flowmechanical boundary
Rudstone-grainstone medium/thinbeds with interbedded bioturbated wackestonesubaerial exposure-hardgroundsfrequent dolomite intervalsheterogeneous facies
Porous, heterogeneousflow unit with brittle beds
clay
flow barrier
Lithology/Sequence Stratigraphyand mechanical units
Rawnsley at el. in press
Morettini et al. submitted
Caliper Porosity ResistivityGamma Ray Density
1. High porosity streaks are better captured
2. Predicted fracture behavior is recognized in production data
3. As a result production strategy was adjusted
Results of modeling in the Natih E
1. Transgressive and regressive hemi-cycles and intervals have variable porosity, permeability and fracture behavior
2. Porosity partitioning occurs on all stratigraphic levels
3. Porosity and fracture partitioning can be captured with high-resolution sequence stratigraphy (HRSS)
4. Reservoir models based on HRSS carry this information
Conclusions and Implications