Reservoir quality of upper Cretaceous Sarvak Formation in an oilfield located in Dezful Embayment, Southwestern Iran

The Upper Cretaceous Sarvak Formation in the Zagros and the Persian Gulf (Southwestern Iran) forms an important reservoir succession. Oil reserves in Sarvak, together with Ilam Formations, make up one-fourth of the total reserves of Iran. This study aimed to determine the petrophysical parameters influencing the reservoir properties within the carbonate sequence of the Sarvak Formation and to identify its productive zones. The latter formation is dominantly composed of limestone and dolomite with subordinate shale units. The studied Sarvak succession has been subdivided into six zones based on petrophysical criteria, whereby zones 3 and 4 have the highest reservoir potential based on the low water saturation and low shale amounts. The main diagenetic processes identified include dolomitization, dissolution, and cementation. The latter process obviously destroys reservoir properties, while dolomitization and dissolution enhance reservoir properties. Measurement of shale volume indicates that its amount is less than four percent of the rock volume. The dominant clay mineral consists of illite or mixed clay minerals with montmorillonite, and their presence is related to well depth and pressure.