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Review of the Permo-Triassic Gas Play in the Arabian Gulf Region

Faqira, Mohammad I.1; Ahmed, Abdelghayoum S.1; Bakhiet, Abdel fattah M.1; Vanlaer, Pierre J.1
1 Exploration Resource Assessment, Saudi Aramco, Dhahran, Saudi Arabia.

Significant amount of non-associated gas reserves are proven from the Permo-Triassic Khuff-Dalan play across the Arabian Gulf region. This play is part of the Paleozoic petroleum system which is sourced by the Silurian base Qusaiba hot shale of the Qalibah Formation. It is sealed by the Triassic Sudair-Aghar Shales and trapped in high relief north-trending anticlines or salt domes.

The Khuff Formation was deposited on a broad shallow marine restricted shelf across the Arabian Platform and consists of interbedded carbonates and evaporites. Four reservoirs named Khuff—A, B, C and D in descending order, are present within the carbonates and display porosity between 3 and 12%. The Khuff reservoirs tend to thicken with improved development toward the east.

Several long north—trending folds were initiated during the Permo-Triassic time across the Arabian Plate. These folds together with salt-cored structures, played a significant role in reservoir development through diagenetic processes. Better reservoir development and communication occur in the salt dome structures, whereas the anticline trends tend to have less reservoir development and no communication across the various Khuff reservoirs.

The hydrocarbon gases of the Khuff reservoirs were sourced from the Silurian base Qusaiba hot shale of the Qalibah Formation. The distribution of these rocks across the Arabian Plate has been influenced by the mid-Carboniferous (Hercynian) Unconformity, in which the Silurian source rocks are preserved in the mid-Carboniferous basins and eroded from the intervening arches.

Hydrocarbon migration is the most critical element of the Khuff play. It requires a faulted trap with sufficiently large throw to connect the Silurian base Qusaiba hot shale source rocks to the Permo-Triassic Khuff reservoirs. All of the Khuff accumulations are trapped in a high relief north-trending anticlines or salt domes.

The quality of the Khuff gas varies with depth in response to increased reservoir temperature. Of the trash gases (H2S, CO2 and N2) H2S is generated in the Khuff reservoirs following a reaction between the hydrocarbons and anhydrites. Geochemistry and petrography have confirmed that H2S in the Khuff reservoirs is due thermo-chemical sulphate reduction (TSR), in which anhydrite is replaced by calcite and sulpher.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009