Late Jurassic Safir evaporite salts, Sab'atayn Basin, Yemen: Lithofacies distribution, cyclicity, and mineralogy

Abstract

This study aims to interpret and evaluate the Late Jurassic Safir rock unit in Sab'atayn Basin in Yemen according to its lithofacies distribution, cyclicity, and mineralogy. The study is conducted on six wells, namely, Halewah-09, Khahtan-01, Azal-25, Al-Nasr-27, Baraqish-01, and Dost Alwihda-01, based on the responses and characteristics of integrated wireline logs. The Safir Member is divided into several cycles and interpreted as a regular rhythmic deposition of halite interbedded with thin clastic (shales and sands) laminations at the top. The cycle diversity is caused by the sedimentation supply invasion (influx) from the hinterland during sea-level regression. The mineralogical analysis of the evaporite salts reveals that the log responses at the studied basin wells have a cylindrical shape, indicating low gamma ray and bulk density readings. Additionally, the high-resistivity log values designate evaporite salts, which also refer to nonpotash evaporite minerals (e.g., halite with gypsum and kieserite) in small quantities. These salts are deposited under brackish or hypersaline aqueous evaporation by periodically entering seawater through a barrier into a restricted basin. The Safir salt in Sab'atayn Basin developed throughout a restricted rift basin connected only to the east and south by the Gulf of Aden across Mukalla Arch, containing grabens and intragraben highs that are the most prosperous areas for hydrocarbon exploration in Yemen, where salt has accumulated by hundreds of meters in thickness.