--> Abstract: Al Rayyan Field: Case Study of a Subtle Structural Trap and Implications for Exploration in the Arabian Gulf, by Graeme Warren, Larry Smith, and Lex Van Wijhe; #90105 (2010)

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AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain

Al Rayyan Field: Case Study of a Subtle Structural Trap and Implications for Exploration in the Arabian Gulf

Graeme Warren1; Larry Smith1; Lex Van Wijhe2

(1) Occidental of Bahrain (Offshore), LLC, Manama, Bahrain.

(2) Occidental Petroleum of Qatar Ltd., Doha, Qatar.

The Al Rayyan Field is an example of a very low relief structure located on the western flank of the Qatar Arch. The structural analysis of the field is an ideal template for the exploration of subtle traps in the region. Different seismic data sets and processing techniques (in both time and depth) have produced ambiguous structures over the field. Isochron mapping of geologically significant intervals successfully resolves the field’s structural evolution through time. This same mapping strategy can be employed as an exploration tool to screen and validate subtle prospects observed in both the time and/or depth domains within the Gulf region.

The Top Early Cretaceous to Top Jurassic isochron is the critical geological interval for understanding the trap geometry of the field. The field is located on a paleo structural nose that previously plunged counter to the present-day regional dip direction. The thinning and faulting evident on the Middle to Upper Cretaceous isochron are in sharp contrast to the structurally featureless Early Cretaceous isochron. The Jurassic isochron thins eastward towards the Qatar Arch and gives no indication of the present day field. The isochron characteristics observed locally are consistent with a regional geological history that begins with stability throughout the Jurassic and Early Cretaceous; is followed by collisional tectonics during the Middle to Late Cretaceous; and culminates with down-warping and northward tilting in the Cenozoic. The latter event transformed the Jurassic reservoir at Al Rayyan from a structural nose into its current low relief, four-way closure geometry.

The foregoing suggests that a valid exploration strategy for the region should consider a search for subtle structural features that formed during the Middle to Late Cretaceous. Paleo-structural noses identified within the Cretaceous section, especially those that are associated with isochron thinning and faulting of the Middle to Late Cretaceous section, represent prime exploration targets. This strategy should help the explorationist distinguish between structurally valid versus velocity-induced leads within these target sections.