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Petrophysics and Petrography of Paleozoic Rocks in Kuwait

Abstract

Recent studies on the hydrocarbon potential of Early Mesozoic reservoir in the great Arabian basin indicate the presence of thermogeneic gas, which might be produced from deeper Paleozoic formations. Petrophysical and petrographical studies have been carried out for the subsurface Permian Khuff and Carboniferous Unayzah Formations in Kuwaiti oil fields, by using wireline logs and core rock samples of nine wells. The petrophysical log interpretation show that the Khuff lithology is mostly dolomites with anhydrite and few limestone's interbeds, while shales predominates its lower part. This facies strongly influenced the porosity values which are generally very low, almost 2 % in average, but with low water saturation of average 21%. The petrographical core analysis indicates the occurrence of dolomitized laminated mud and dolomitized calcareinte facies. On the contrary, the Unayzah lithology is mostly clastics of fine- sandstones, siltstones, and claystones with thin beds of argillaceous limestone and many dark bituminous shale intervals. The porosity values ranges from 0 to 20 %, particularly in the upper part of the formation, but with a relatively high water saturation. The petrographical core analysis indicates local metamorphosed carbonaceous shale at the lower part of the formation, changed to siliciclastic wackestone at the upper part. These facies are manifested by the microfabrics and micro deformation structures. The study revealed that the Unayzah Fm. has a better reservoir quality and probable gas bearing zones than the Khuff Formation.