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AAPG Bulletin


AAPG Bulletin, V. 92, No. 7 (July 2008), P. 885-917.

Copyright copy2008. The American Association of Petroleum Geologists. All rights reserved.


The Khazzan gas accumulation, a giant combination trap in the Cambrian Barik Sandstone Member, Sultanate of Oman: Implications for Cambrian petroleum systems and reservoirs

John A. Millson,1 Jamie G. Quin,2 Erdem Idiz,3 Peter Turner,4 Ahmed Al-Harthy5

1Exploration Technical Assurance, Petroleum Development Oman, P.O. Box 81, Muscat 100, Sultanate of Oman; [email protected]
2Statoil ASA, N-7501 Stjordal, Norway
3Global Exploration Adviser, Shell International Exploration and Production, B.V. Kessler Park 1, 2288 GS Rijswijk (ZH), Netherlands
4Turner Geoconsultants Ltd., 7 Carlton Croft, Streetly, West Midlands, B743JT, United Kingdom
5Occidental, P.O. Box 2271, Ruwi 112, Sultanate of Oman


Khazzan is a giant tight-gas accumulation located in northern Oman. The accumulation is associated with Cambrian Barik Sandstone Member reservoirs, in a semiregional combination (stratigraphic-structural) trap. This article outlines the background to the discovery of Khazzan and describes our understanding of its geology and petroleum systems and the study work used to support screening, appraisal, and development strategies for the Khazzan accumulation. The stratigraphic element of the trap is associated with a northerly thinning and transition of continental, fluvial braid-plain and shoreface sandstones into offshore mud rocks. The structural element of the trap formed as a result of the compactional drape of these reservoir units and the later structuring associated with an underlying, long-lived intrabasin high.

The integration of multiple correlation techniques (well-log correlation, recognition of changes in core facies and ichnofacies and magnetostratigraphy) has helped to define an intrareservoir correlation framework for the Barik Sandstone Member, with a resolution of approximately less than or equal to 1 m.y., allowing detailed insights into stratigraphic and areal controls on hydrocarbon compositional variations, trapping mechanisms, reservoirs, and reservoir connectivity.

Fluvial sandstones within the Khazzan stratigraphic pinch-out form better reservoirs. The stratigraphic framework developed indicates that these fluvial units are associated with discrete, geographically extensive, progradation events. The association of production with discrete reservoir levels and areas allows a robust semipredictive regional model for targeting better reservoirs and highlights a scope for an additional intra-Barik stratigraphic trapping potential regionally. Enhanced reservoir quality within the more productive reservoirs is attributed to depositional and possibly hydrocarbon charge controls on secondary porosity, and it is complex.

Subtle crest-to-flank compositional variations in hydrocarbon type across the gas accumulation hint at complex hydrocarbon charge and mixing between two structural domains and petroleum systems before and during Barik deposition.

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