Jurassic Carbonate Reservoirs, Northern Saudi Arabia: Distribution, Architecture and Characterization

Tom Harland, David Tang, Paul Lawrence, and Greg Gregory
Saudi Aramco, 31311 Dhahran, Saudi Arabia

A total of fourteen carbonate reservoir horizons are proven in the Jurassic sequence of northern Saudi Arabia, providing several super-giant oilfields, other accumulations, and numerous further opportunities. Most reservoir units comprise higher energy shoal and shoal-related sediments, distribution of which was controlled by the interrelationship between evolving basin configuration, eustacy, and infill.
In the Mid-Late Jurassic there were two distinct phases of basin development. The Dhruma Basin developed by differential subsidence in the late Aalenian-early Bajocian. Earliest reservoir units (Faridah) are essentially marginal and off-lapped into the basin only to a relatively minor extent. Successive reservoir units each show progressive off-lap as subsidence slowed and the basin became filled. The latest reservoir unit (Lower Fadhili) shows extensive spread across the region.
Renewed differential subsidence in the earliest Callovian established the Hanifa Basin. Again, the earliest reservoir units (Upper Fadhili, Hadriya) are essentially marginal and successive reservoir units (Hanifa 1-4) show progressive off-lap. Major draw-down occurred near top-Hanifa level (late Oxfordian), exposing the basin margins and causing significant down-lap. Infilling Jubaila sediments are non-reservoir except in limited shoulder areas at the margins (erosional lows?) but the ensuing reservoir units (Arab D through A) spread rapidly to infill the basin. Hith anhydrites complete basin fill and form the regional Jurassic seal.
Thorough understanding of overall reservoir distribution, combined with reservoir architecture and rock properties is fundamental to understanding not only where to look and what might be found, but also provides a sound template for understanding probable migration paths, plays, systematic variations in reservoir character, and many additional factors.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece