--> --> Depositional Environments, Architecture and Diagenesis of Fahud Field, Oman, by Volker C. Vahrenkamp, Alia Al Bahry, Talal Al Musallami, Abhijit Mookerjee, Wadie Mansour, Richard Singleton, Cathy Hollis, Peter Homewood, Henk Droste, Carine Grelaud, Philippe Razin, Quintin Davies, Boris Kostic, Conxita Taberner, and Mateu Esteban; #90052 (2006)

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Depositional Environments, Architecture and Diagenesis of Fahud Field, Oman

Volker C. Vahrenkamp1, Alia Al Bahry1, Talal Al Musallami1, Abhijit Mookerjee1, Wadie Mansour1, Richard Singleton1, Cathy Hollis2, Peter Homewood3, Henk Droste3, Carine Grelaud3, Philippe Razin4, Quintin Davies5, Boris Kostic5, Conxita Taberner6, and Mateu Esteban7
1 Petroleum Development Oman, Muscat, Oman
2 Shell International Exploration and Production, Risjswijk, Netherlands
3 Sultan Qaboos University, Al Khod, Oman
4 Bordeaux University, Bordeaux, France
5 Badley Ashton and Associates, Lincolnshire, England
6 Institute of Earth Sciences, CSIC, Barcelona, Spain
7 Carbonates International Iberia, S.L, Caimari, Mallorca, Spain

Fahud Field is a giant fractured carbonate reservoir in the Sultanate of Oman. It is contained in the Natih Formation, a 450m thick section of Albian to Turonian high porosity, low permeability shallow water carbonates. Deposition occurred over a period of three regionally correlatable third order cycles in environments ranging from source rocks deposited in intrashelf basins, mud-dominated wacke/packstones of slope environments, coarse rudist sand shoals, tidal flats to back-shoal lagoons. On a large scale reservoir architecture is layer-cake and well constrained by some 400 wells. However, a close look at seismic, outcrop analogues and performance indicated the likelihood of significant internal heterogeneity.

In support of further development activities some 1800m of new cores were taken to investigate:

  • Depositional environments & architecture (lateral facies variations & cycle stacking patterns)
  • Diagenesis (paragenetic sequence, impact of subaerial exposure including lateral structurally related changes and subsequent burial)
  • Distribution of petrophysical properties (standard & SCAL).

Core observations are anchored by extensive outcrop analogue studies, detailed mapping of 3D seismic, a wide variety of logs and the analysis of production behaviour. They suggest that reservoir properties and behaviour are directly related to a complex interplay between depositional heterogeneities related to aggrading and prograding carbonate sequences (clinoforms), cycle top alterations during several episodes of early exposure and porosity creation during burial diagenesis.

Findings from the core analysis are key elements to constrain ranges of uncertainties incoporated into 3D static and dynamic reservoir models, which were built to assess production forecasts and economics of various development options.