porosity partitioning in sedimentary cycles: implications...

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




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





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


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

porosity partitioning in sedimentary cycles: implications...

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