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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

Seismic Geomorphology of Palaeozic Reservoirs in the South Ghawar Area, Saudi Arabia

Stanley R. Wharton1; Thomas Loretto2

(1) Exploration, Saudi Aramco, Dhahran, Saudi Arabia.

(2) Gas Reservoir Characterisation, Saudi Aramco, Dhahran, Saudi Arabia.

The evaluation of Paleozoic depositional megasequences in the South Ghawar area is complex, as the area has been influenced by periods of early Paleozoic glaciation, marine transgression, and tectonism. Early Ordovician glacial advance and retreat generated distinct elongated paleovalleys within which subsequent megasequence deposition occurred. The Hercynian orogeny influenced the paleotopography, upon which Carboniferous and Permian sequences have distinct onlapping relationships to the north and west of the Hercynian depocenter. A seismic/geomorphological analysis was applied in the basin in order to elucidate depositional styles of Paleozoic sequences, onlap relationships, unconformities, and tectonic styles associated with hydrocarbon migration.

Using pre-stack time migrated data, seismic attribute volumes were generated for multi-volume, multi-attribute analysis. The geomorphological extent of the depositional sequences was analyzed, in order to reflect the infilling stages of sequences within and beyond a major paleovalley near the base of the Qusaiba. Key mapped horizons in Paleozoic megasequences from Permian to near Base Qusaiba enabled assessment of isochores, which indicate thinning trends towards the flanks of the depocenter. Both the Wudayhi and Ghazal structures are major Hercynian eroded features that controlled Carboniferous Unayzah deposition. Well data and palynological picks were used to constrain key paleosurfaces, and seismic facies analysis calibrated to wells helped define gross depositional environments that have variable progradational directions through time. The multi-volume, multi-attribute data analyses assisted with evaluation of the depositional sequences. The steeper flanks of the basin, however, have varying sequence relationships and complexities related to pinchouts and drapes onto Hercynian-related structure.

Structural analysis using automatic fault mapping routines on coherency data enabled quick assessment of complex subregional structural styles that are dominated by strike-slip tectonics.

The seismic geomorphology approach enabled the definition of the morphology of the sequences and depositional styles within the basin. Although unconformity traps on basin flanks were more difficult to define, they present significant exploration opportunities. This approach enables the targeting of key areas for exploration, with focus on unconventional traps