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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

Sequence Stratigraphy and Reservoir Compartmentalization in the Lower Wasia, Saudi Arabia

Abdulaziz A. Al-Duaiji1; Mohammed J. Al-Mahmoud1; Mesbah H. Khalil1; Homoud R. Al Anzi1

(1) Saudi Aramco, Dhahran, Saudi Arabia.

High resolution sequence stratigrphy analysis was applied at the Lower part of the Wasia Formation (Khafji, Safaniya and Mauddud members) of Albian age in the offshore Saudi Arabia. Core analysis, wire-line logs, biostratigraphy and fluid data were used in the analysis. Two 3rd order sequences were identified within the Lower part of the Wasia Formation.

The Wasia Formation (Albian/Turonian) in Saudi Arabia is represented by seven members; from bottom to top are the Khafji, Safaniya, Mauddud, Wara, Ahmadi, Rumaila and Mishrif. The Wasia is bounded by two pronounced regional unconformities related to major tectonic events: the pre-Wasia (Albian/Aptian) and pre-Aruma (Campanian/Turonian).

The lower sequence starts at the base of the Khafji member with the low-stand Khafji main sand followed by transgressive Khafji sand stringers with a maximum flooding limestone marker called Dair limestone. This sequence was terminated with the high-stand Khafji stray sands; a very thin continuous sand overlaying the Dair limestone. The upper sequence starts with the low-stand Safaniya reservoir sandstone followed by the transgressive and maximum flooding surface of the Mauddud limestone. The sequence ends with the high stand thin carbonates and shales of the upper Mauddud. Outcrop data has been correlated with the subsurface to establish the regional framework.

Detailed tectono-stratigraphic analysis of the Lower Wasia in the offshore fields indicates that the Lower Khafji main sand was deposited as fluvial filling of the tectonically-controlled irregular basin topography. The deposition of the remaining section of the two sequences was primarily controlled by the sea level eustacy with weak tectonic imprints. Tertiary reactivation of the faults cutting the pre-Wasia has resulted in compartmentalization of the Lower Wasia reservoirs.