A Depositional Model in the Arabian Intrashelf Basin: The Upper Jurassic Hanifa Reservoir of Abqaiq Field, Saudi Arabia

BAILEY, DONALD L., Saudi Aramco, Dhahran, Saudi Arabia

Abqaiq field is a northeast-trending anticline approximately 60 km long and 12 km wide and contains several reservoirs. The 100 m thick Hanifa Reservoir interval consists of interlayered peloidal packstone and wackestone with subordinate dolomite and anhydrite. During an Upper Jurassic relative sea level lowstand, paleotopography within the Arabian Intrashelf basin localized fine-grained packstone into isolated mounds over the Abqaiq South Dome area, while muddier facies were being deposited over the North Nose. A similar depositional setting for the Abqaiq Hanifa is found in Belize where numerous isolated carbonate buildups are developed on paleohighs within the Belize Intrashelf basin. The Abqaiq Hanifa carbonate mound was zoned using sequence stratigraphy as a conceptual framework o ensure that chronostratigraphic relationships were honored, and that the subsequent computer model would therefore accurately reflect spatial porosity continuity within the reservoir.

The Hanifa Reservoir was subdivided into five widely correlative zones that approximate separate parasequences, each beginning with tight mudstone-wackestone and grading upward into porous wackestone-packstone. The Abqaiq Hanifa parasequence set exhibits aggradational to progradational strata stacking patterns and is interpreted to be part of the lowstand systems tract (LST) found above the sequence boundary at approximately 144 Ma in early Kimmeridgian time. Sequence stratigraphy interpretations are based on regional wireline log correlations combined with core descriptions and show the Abqaiq Hanifa to be time equivalent to only the upper few meters of the Hanifa Reservoir in fields located near the Arabian Intrashelf basin edge, like Berri field to the north. Most of the main Berri reservoir is part of the highstand systems tract (HST) of the underlying sequence. The packstones of the Abqaiq Hanifa were deposited under low-energy conditions within the intrashelf basin during relative sea level lowstand after the grainstones of the Berri Hanifa were deposited under high-energy conditions on the intrashelf basin edge during the previous highstand. In addition to reservoir modeling utility, these two general intrashelf basin settings have potential for stratigraphic traps. Wherever reservoir-quality rock can be found, proximity to the Hanifa/Hadriya source rocks--the source for much of Saudi Arabia's vast reserves--makes the Hanifa a favorable exploration target.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)