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Carbonate Reservoir Rock Typing A Case Study in North Oman

Carbonate Reservoir Rock Typing A Case Study in North Oman. Presented by: Majid Hasani, PDO SPWLA conference Abu Dhabi 15 th Feb – 18 th Feb 2010. Outline. Field introduction General field data Basic Reservoir Data Rudist types The issue Classical approach for Carbonate Reservoirs

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Carbonate Reservoir Rock Typing A Case Study in North Oman

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  1. Carbonate Reservoir Rock TypingA Case Study in North Oman Presented by: Majid Hasani, PDO SPWLA conference Abu Dhabi 15th Feb – 18th Feb 2010

  2. Outline • Field introduction • General field data • Basic Reservoir Data • Rudist types • The issue • Classical approach for Carbonate Reservoirs • RFC & RRT • Integrated Modelling Workflow! • Optimising RRT • Conclusion

  3. General field data • Location: North of Oman • The field is subdivided in a number of areas, based on structure and reservoir development: Main Area, Eastern Satellite, Southwest Area. • Lower Cretaceous rudist reef complex • Very heterogeneous reservoir properties; their effect on well inflow is poorly understood.

  4. Basic Reservoir Data

  5. Rudist types Rudists are a group of box, tube or ring shaped marine heterodont bivalves that arose during the Jurassic, and became so diverse during the Cretaceous that they were major reef-building organisms in the Tethys Ocean. Wikipedia, the free encyclopedia Schumann & Steuber 1997

  6. Paleogeographic map of the Early Aptian in some of Part the Arabian Palate

  7. A type log • Variable geological facies within well level

  8. Well example of the large variation in permeability seen in the Field. RRT 0.5-1.5 RRT 1-1.5

  9. The issue !

  10. Permeability Variation Channel well Permeability ranges ~ 3 decades Mud dominated *Coloured per well High variability, No unique Poro Perm relation

  11. Classical approach for Carbonate Reservoirs

  12. RFC & RRT • RFC: Rock Fabric Classification • Assigned to each different geological facies, discrete value; ex: • RFC =1  Grainstone • RFC = 2  Grain-Dominated Packstone • RFC = 3  Mud-Dominated Wackstone • Lucia used RFC to compute permeability for different geological facies (SPE 71336 by Lucia 2001) • These RFC can only be obtained in cored wells where geological facies have been defined • RRT: Reservoir Rock Type • Link geological facies to well logs variables (interparticle porosity & water saturation) • RRT is used in all logged wells to generate rock typing (instead of RFC) in uncored wells • it is a continuous variable used to mimic RFC

  13. Permeability and RRT RFC 1 AH-10H1: 5061ft RFC 1 RFC 1 RFC 1 RFC 2 RFC 2 RFC 2 RFC 3 RFC 3 RFC 3+ RFC 3+

  14. RFC to RRT RRT coefficients Lucia equation parameters Original Lucia equation

  15. Integrated Modelling Workflow!

  16. Permeability Integration Workflow • RRT and Lucia equation • RRT computed from porosity and water Saturation • A process of iteration through history match in dynamic model and Lucia Rock fabric line are used to fix RRT coefficients. • The computed RRT is found to fit in to Lucia Rock fabric number

  17. HM Integration Workflow DM upscale QA/QC. Submit HM runs in DM Analyse Liquid Match Run sensitivities* Update SM Liq HM OK? PVT+Pc+Kr Y Feedback to PP for updating RRT & Lucia perm N Feedback to PG for SM update Check connectivity and adjust perm HM: history match SM: static model DM: dynamic model N Adjust Kr and submit runs in DM HM OK? HM OK? Check Saturation Match N Y Y Forecast NFA and compare with DCA

  18. Optimising RRT • A process of iteration is used to optimise RRT coefficients (dynamic model HM) Matching only with core perm After HM iteration History Production History Production Model Production Model Production Black: Total fluid Blue: Water Red: Oil Black: Total fluid Blue: Water Red: Oil

  19. RFC match with RRT (after HM) RFC *Colour indicates RRT

  20. Lucia permeability match with core Perm POR SH GR DEN NEU DEN RES Lucia perm Core perm

  21. RRT match with geological facies SH Perm POR GR DEN RES Geological facies Rudist Packstone RRT 0.5 – 1.7 RRT Rudist Wackstone RRT 2.2 – 2.9 Algal Mudstone RRT 3.2 – 3.9

  22. Conclusion • Predicting permeability in complex heterogeneous carbonate reservoir was initially carried out by the standard Lucia approach • RRT is used instead of RFC to compute permeability in uncored wells after calibrating RRT in cored wells • RRT coefficients should be optimized by history matching the total field liquid off-take

  23. !|! Thanks !|!

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