AAPG Middle East Geoscience Technology Workshop, Integrated Emerging Exploration Concepts

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Mapping of Conceptual Stratigraphic Traps in the Southern Flank of Rub Al’ Khali Basin (Block 49, Oman)

Abstract

Block 49 is located in the southern flank of the Rub Al’ Khali basin. The south-eastern part of the block straddles the Ghudun-Khasfah High on the western margin of the prolific South Oman Salt Basin. It is a frontier exploration block with potentially two working plays sourced from the Early Silurian Sahmah Formation, equivalent to the Qusaiba “hot shale” of Saudi Arabia. ‘Sahmah-Haushi’ play is long-time known in the region with analogue producing fields in the neighbouring block 7. The play consists of Silurian Sahmah source rock, Permo-Carbonaferous Haushi Group sandstone reservoirs capped with Upper Gharif and Khuff shaly sections as regional seals. The hydrocarbon type is the light, quality oil with average API of 440. The other play that is likely present but not yet fully recognized in the block is the ‘Sahmah-Late Ordovician Palaeovalley/ Buried Hill’ play. This type of play is well known from the North Africa (Algeria, Libya) and the Middle East (Jordan, Syria, Iraq and Saudi Arabia), where Late Ordovician glaciogenic sandstones form massive oil and gas reservoirs, charged from the overlain Early Silurian source rock. The reservoirs are charged by upward migration from down-faulted Silurian source rock and/or in some cases, by downward migration from the same source rock, filling the channels from top to bottom. The potential for conceptual stratigraphic trap opportunities was not yet tested in this block. The block is regarded as fairly explored as it is covered by non-uniform 2D seismic grids of various vintages. However, the quality of seismic data is rather poor and limited seismic resolution is largely effected by multiples. Nine wells have been previously drilled and abandoned in this block, five of them with minor hydrocarbon shows. The shows are confined to an interval interpreted as Late Ordovician sandstones of Hasirah Formation, lying directly below the Early Silurian source rock of Sahmah Formation. A reasonably thick source rock interval with relatively high TOC are found in the wells within block 49 and surrounding area. Extensive seismic interpretation using sequence stratigraphy approach was done on existing reprocessed seismic lines, as well as on new acquired 2D and 3D seismic data. Results reveal a number of stratigraphic and combination traps within pre-Hercynian and Carboniferous-Permian deposits.