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

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. John Millson holds a B.Sc. (honors geology) degree and a Ph.D. from Aston University in Birmingham, United Kingdom and the University of Wales, Abersytwyth. Joining the oil industry as a petroleum geologist in 1985, he has worked in the United Kingdom, Nigeria, Netherlands, and Oman, with some 11 years of working on various aspects of the geology of Oman. His main interests include tectonostratigraphy and unconventional hydrocarbon resources. Jamie Quin is a geologist for Statoil-Hydro. Since joining the oil industry in 2001, he has worked on assets in Oman (for Badley Ashton and Associates), Libya (for Repsol YPF), and Norway (Statoil). He holds a B.Sc. degree from the University of Glasgow, an M.Sc. degree from Royal Holloway, University of London, and a Ph.D. from Trinity College Dublin. Erdem Idiz is currently a global exploration adviser for Exploration New Ventures with Shell International Exploration and Production in the Netherlands. He received his M.Sc. degree in geology (1981) and Ph.D. in geochemistry (1987) from the University of California, Los Angeles (UCLA). After a postdoctorate at the Institut Francais du Petrole, he joined Shell in 1988, working in research and applications as a geochemist and basin modeler in the Netherlands, Germany, and Canada. His research interests are petroleum systems analysis, biomarkers, and stable isotopes. Peter Turner holds degrees from Cardiff and Leicester Universities and was a reader in earth sciences at the University of Birmingham in the United Kingdom from 1988 to 2006 where he was head of the Petroleum Geoscience Group. His research includes paleomagnetism, sedimentology, and hydrocarbon reservoirs, and since retiring from university life, he has worked as a full-time consultant focusing on exploration in north and west Africa and China. No details available.