Porosity partitioning in sedimentary cycles: implications for reservoir modeling

Transcription

1 Porosity partitioning in sedimentary cycles: implications for reservoir modeling Gregor P. Eberli 1), Langhorne B. Smith 2), Elena Morettini 3), Layaan Al-Kharusi 1) 1) Comparative Sedimentology Laboratory, University of Miami 2) New York State Museum, Albany, New York 3) Carbonate Development Team, Shell, Rijswijk, The Netherlands

2 1. Facies and diagenetic partitioning often divides sedimentary cycles (genetic units) into transgressive and regressive hemicycles with variable porosity and fracture behavior 2. Porosity partitioning follows stratigraphic cyclicity and can be implemented in reservoir modeling

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4 Exposure Regressive part Regressive Hemicycle Holocene Mud Bank Exposure Transgressive part Turn around Transgressive Hemicycle Pleistocene (Enos and Perkins, 1977)

5 Principle of Facies Partitioning Different facies associations are produced during relative sea-level rise versus sealevel fall as a result of differences in direction and amount of energy differences in the fauna and flora differences in the preservation potential

6 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

7 Transgression marine cementatio dolomitization Regression meteoric lense marine dissolution cementation meteoric dissolutio cementation limestone dolomite

8 Porosity Partitioning Porosity partitioning occurs in genetic unit sets of genetic units sequences and supersequences

9 Sheep Mountain Anticline: Mississippian Madison Formation

10 Genetic unit in the Mississippian Madison Formation cycle lithology environment regressive hemicycle flooding surface skeletal packgrainstone marine shelf Beach/tidal bars shoal middle shoreface 1mm turnaround transgressive hemicycle corals laminated stromatolites coarse grainstone skeletal packgrainstone marine shelf lagoonal tidal shoal 0.25mm

11 3rd order 4th order 5th order Diagenetic Partitioning in the genetic units of the Madison Formation at Sheep Mountain Regressive Hemicycle Transgressive Hemicycle Limestone Dolomite

12 micycles Sheep Mountain Low Angle Limb-C Lithology Mechanica Units 120 Mechanical Boundary Average Fracture Spacing = 7cm Are They Mechanical Boundaries? Mechanical Unit 6 Total No. of Fractures No. of Fractures Which Terminate at Boundary Mechanical Unit 5 Mechanical Boundary 5 No. of Fractueres 80 Mechanical Boundary 2 60 Mechanical Boundary 3 Average Fracture Mechanical Unit 4 40 Spacing = 31cm Mechanical Boundary 4 Average Fracture 20 Spacing = 20cm Mechanical Unit 3 Average Fracture Spacing 0 = 22cm Mechanical Unit 2 Average Fracture Spacing = 4cm Mechanical Unit 1 M W P G

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15 High Resolution Sequence Stratigraphy The Method for Capturing porosity partitioning Core analysis Determination of genetic units 1) identification of facies trends on cores 2) separation into packages of transgressive/regressive hemicycles 3) stacking of the genetic units into hierarchical higher cycles Core to Log correlation Calibrate core to the logs Correlation of calibrated logs to uncored wells Model input Determination of appropriate cycle hierarchy for reservoir modeling

16 Rudist platform Mid Ramp Outer Ramp Intrashelf Basin Outcrops Oil and gas field Well locations

17 equence Stratigraphic Framework Fahud Field Natih Field FN 176 FN 3 NW 81 N7 clayey marls organic-rich limestones Mudstone Bioclastic grainstones to packsto Rudist floatstone/rudstone Maximum flooding surface 3rd order 3rd order Sequence boundary Decrease in accommodation spac (regression) d after Van Buchem et al ed to AAPG;Van Buchem et al Increase in accommodation space (trangression)

18 Facies Natih E egressive Deposits Shoal arse-grained bioclastic grainstones and rudstones rbitolina-rich grainstones and rudist bioclasts) Shallow Shelf (with redistributed shoal sediments) oturbated, muddy pelletal wackestones ansgressive Deposits lletal Wackestones with clay and chert nodules Morettini et al. submitte

19 SMALL SCALE CYCLE/GENETIC UNIT NATIH E FORMATION K Φ md % HRSS Cycles Environment of sedimentation Microfacies Rudist buildup Inter rudist/buildup Rudist buildup Inter rudist/buildup Rudist buildup Inter rudist/buildup

20 Lithology/Sequence Stratigraphy and mechanical units Lithology m w p g r 4th 3rd Lithostrat. Units D5 Et 1 Er 2 Et 2 Er 3 mfs Et 3 Er 4 Et 4 Er 5 Et 5 Er 6 Et 6 mfs E5 E1 E2 E3 E4a E4b marine meteoric marine/meteoric Facies, Diagenesis Bedding Character and Clay clay Rudstone-grainstone medium/thin beds with interbedded bioturbated wackestone subaerial exposure-hardgrounds frequent dolomite intervals heterogeneous facies flooding zone wackestone with clay Exposure surface Wacke-packstone and interbedded coarse rudstones; thick beds Marine diagenesis Sparse dolomite intervals flooding surface argillaceous wackestone Bioturbated wacke-packstone with chert submarine cementation clay Proposed Mechanical and Flow Units Low flow Porous, heterogeneous flow unit with brittle beds Low flow mechanical boundary Porous, homogeneous flow unit ductile unit with brittle layers Low flow mechanical boundary Homogeneous less porous flow unit ductile unit flow barrier Rawnsley at el. in press

21 Caliper Porosity Resistivity Gamma Ray Density Morettini et al. submitted

22 Results of modeling in the Natih E 1. High porosity streaks are better captured 2. Predicted fracture behavior is recognized in production data 3. As a result production strategy was adjusted

23 Conclusions and Implications 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