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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

A Model for Gas Migration into the Khuff Reservoirs

Abdulkader M. Afifi1

(1) Saudi Aramco, Dhahran, Saudi Arabia.

In the Arabian Gulf region, the distribution of gas accumulations in the Permo-Triassic Khuff Formation roughly coincides with the distribution of the terminal Proterozoic (Eidacaran) Hormuz salt basins. This is attributed to the breaching of thick shale/ carbonate/ anhydrite seals at the base of Khuff Formation by faults that propagated upwards into the Khuff during the initial development of high-relief salt domes. Once gas entered the Khuff reservoirs, it migrated laterally into available structures and also spilled towards the edge of the salt basins, where it was trapped in the initial line of structures along the flanks of the salt basins. For example, the Khuff gas in the Ghawar structure, which is located to the west of the Northern Gulf salt basin, was charged laterally from the northeast by progressive spillage through the Qatif and Abqaiq structures. This is indicated by several lines of evidence such as the absence of Khuff gas in structural closures located to the west, east, and south of Ghawar, the presence of effective seals at the base of the Khuff, and the difficulty in charging the Khuff reservoirs vertically through reactivated Hercynian faults that also trapped gas in the underlying Permo-Carboniferous and Devonian sandstone reservoirs.

On a regional scale, this model accounts for the spatial association of the Khuff gas accumulations with the salt basins, and the more widespread presence of gas in Paleozoic (pre-Khuff) reservoirs both within and outside the salt basins.