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Abstract

(Begin page 1817)

AAPG Bulletin, V. 85, No. 10 (October 2001), P. 1817-1845.

Copyright ©2001. The American Association of Petroleum Geologists. All rights reserved.

Petroleum systems of Oman: Charge timing and risks

J. Previous HitMNext Hit. J. Terken,1 N. L. Frewin,2 S. L. Indrelid3

1NAM Business Unit Gas Land, Beekweg 31, Postbus 1, 7760AA Schoonebeek, Netherlands; email: [email protected]
2Petroleum Development Oman; email: [email protected]
3Petroleum Development Oman; email: [email protected]

AUTHORS

Jos J. Previous HitMTop. Terken joined Shell in 1982 and has worked in the Netherlands, Brunei, New Zealand, and Indonesia. In 1993 he joined Petroleum Development Oman (PDO) as a senior review geologist/basin modeler in the regional studies team. In close cooperation with the geochemistry group he modeled and mapped the petroleum systems of Oman. Since November 1999 he has been a senior production geologist for the Nederlandse Aardolie Maatschappij in the Netherlands. Jos received an M.Sc. degree in geology/sedimentology from the University of Utrecht in 1982.

Neil L. Frewin is currently a member of Shell International's technology innovation team in the Netherlands. Before 2001, he was senior petroleum geochemist for PDO, where he led the hydrocarbon modeling group. Prior to being posted to PDO in 1997, he worked for Shell International in the Netherlands as a research geochemist. He holds a B.Sc. degree in geology from the University of Wales and a Ph.D. in geology/geochemistry from the University of London. Neil spent a postdoctoral year researching biomarker technologies at Delft University and NIOZ, the Netherlands.

Sarah L. Indrelid joined Shell in 1993. Prior to being posted to PDO in 1998, she worked for Shell International in the Netherlands as a research geologist on thermal and pressure modeling. After one year as senior basin modeler in the hydrocarbon modeling group she is currently a senior production geologist for PDO. She holds a B.A. degree in natural sciences from the University of Cambridge and a Ph.D. in geology from the University of Oxford.

ACKNOWLEDGMENTS

We acknowledge the contributions of various PDO geoscientists, notably Ramon Loosveld, Peter Nederlof, Mike Naylor, Jean Borgomano, Wiekert Visser, Geert Konert, Jeroen Peters, Joachim Amthor, Paul Tricker, and Pascal Richard. We thank the Newcastle Research Group, in particular Steve Larter and Baz Bennett, for geochemical analyses and discussions. Jeremy Dahl and Mike Moldowan at Stanford University are acknowledged for diamondoid analyses. Geochemists at Shell's research and technology group (SEPTAR) in the Netherlands are acknowledged for numerous reliable analyses over 20 years and continuing discussions on Oman's petroleum systems. In particular, we thank Math Kohnen, Jan Kleingeld, Kees Kommeren, and Johan Buiskool Toxopeus for their extensive input. Christopher Kendall, R. Scolaro, and especially Gerard Demaison are thanked for their constructive reviews. We wish to thank the Ministry of Oil and Gas of the Sultanate of Oman for permission to publish this article.

ABSTRACT

After 35 years of exploration, creaming of the conventional plays in Oman is nearly complete, and consequently, the search has commenced for new, less obvious plays. Many of the new opportunities occur beyond the known hydrocarbon provinces and are considered to have significant charge risks. To define these risks, extensive basin modeling studies have been conducted in recent years.

Modeling and empirical data show that Mesozoic and Cenozoic kitchen areas are restricted to western north Oman, the only areas currently buried at their maximum temperature. Large parts of north and central Oman depend on lateral migration from these kitchens for their charge. Progressive uplift of the east flank and basin inversion since the middle Paleozoic provides favorable conditions for long-distance migration in the post-Carboniferous interval. In central Oman, geochemical tracer molecules (benzocarbazoles) suggest that a north-south-trending, reactivated basement grain has funneled charge up to 300 km southeastward. Charge risks increase in the deeper sequence, in which eastward migrating hydrocarbons have to traverse the Ghaba salt basin, a pronounced syncline at depths greater than 3 km. The south Oman salt basin is currently cool because of shallow depths and hydrodynamic fluid-flow activity. The shallow post-Cambrian reservoirs rely on storage of early (Cambrian-Ordovician) charge by the Ara salt (Cambrian) sequence, followed by release of hydrocarbons as the salt edge retreats through time.

Basin modeling has outlined the extent of the different petroleum systems and provided us with risk maps to guide our next exploration phase. It has revitalized some of the mature plays, for instance the Gharif Formation, where oil exploration is now focused along Late Cretaceous and Tertiary migration paths. Deeper sections are envisaged to have significant scope for gas.

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