Sedimentary facies study of the Faraghan Formation in the Persian Gulf fields and reservoir quality evaluation using well logs
Subject Areas :
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Keywords: Faraghan Formation, Sedimentary facies, log facies, reservoir quality.,
Abstract :
Reservoir rocks are of great importance in reservoir studies in terms of hydrocarbon storage. In recent years, following increased exploration activities and improved exploration methods, reservoir rocks related to the Paleozoic era have gained special importance throughout the Middle East, especially in Southern part of the Persian Gulf. The lithological characteristics and depositional environment of this sequence are important parameters that affect their reservoir quality. Therefore, this study examines the sedimentological characteristics and determines the facies of the Faraghan Formation using sedimentological studies in four wells from Iran’s offshore fields and correlates it using the concept of log facies in fields that have been drilled up to the Faraghan Formation. Based on petrographic studies of drilling cuttings, six petrofacies including sandstone, sandy shale, red siltstone, black and green shale, limestone, and mixed petrofacies were identified in the cored well. These petrofacies were classified into four depositional environments (accompanied by facies associations): coastal plain, shoreface, transitional, and offshore. Based on the available data from well logs, 6 log facies were identified in a well where sedimentary facies were extracted. The correlation of the log facies results with the sedimentary facies and the facies association indicate good correlation. Log facies 1 is composed of limestone, log facies 2 and 3 are sandy, log facies 4 is sandy with shale content, log facies 5 is shaly, and log facies 6 contains red-colored shales. The variation in log facies distribution in the wells drilled in the Faraghan Formation indicates significant changes in the lateral depositional environment of the Faraghan Formation. The reservoir quality analysis of the log facies indicates that log facies 2 and 4 have the best reservoir quality. These mentioned facies are most abundant in the Faraqhan 2 (F2) and Faraqhan 1 (F1) sections. Therefore, it can be concluded that the best interval in terms of reservoir quality belongs to zones 2 and 1 of the Faraqhan formation.
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