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Reservoir quality and K-Ar age dating of the pre-Khuff section of Kuwait


 Based on studies of petrographic thin sections from core and cutting samples, the pre-Permian siliciclastics in four deep wells in southern Kuwait were found to be tight. Three of these wells are located on the crestal region of the Burgan Arch, and one on the Umm Gudair anticline. These clastics were encountered beneath a thin brick-red shale of unknown thickness, immediately below the pre-Khuff unconformity at the base of the Permian-Triassic Khuff Formation. The pre-Khuff clastics range in thickness from a few tens of feet to more than 4,000 ft, and overlie a Proterozoic argillite (Economic Basement). Based on Illite Age Analysis (IAA) of samples from cores, the depositional K-Ar age of the pre-Khuff clastics is estimated to be younger than 509 Ma (90 percent confidence interval: 544–481 Ma, i.e. Cambrian-Early Ordovician). The argillite was uplifted through the 300°C isotherm at about 611 Ma (90% confidence interval: 635-588 Ma, i.e Late Proterozoic); its deposition and metamorphism preceded this date. During the Paleozoic, the pre-Khuff clastics were buried to depths of 10,000–15,000 ft, but were subsequently uplifted in the Late Paleozoic. IAA diagenetic K-Ar ages of the Economic Basement (421 Ma; 90 percent confidence interval: 442-397 Ma; Late Ordovician-Early Devonian) and pre-Khuff clastics (369 Ma; 90 percent confidence interval: 404–337 Ma, i.e. Devonian-Early Carboniferous) indicate that by these times the pre-Khuff section was already deposited and undergoing burial diagenesis. The interpretation of gravity data indicates that in Paleozoic basinal regions (e.g. between the Burgan Arch and Umm Gudair Anticline), the Paleozoic sedimentary section is likely to be more complete and may exceed 10,000 ft in thickness.