Sedimentology
Saeideh Rahmani; Behrouz Rafiei
Abstract
The Oligo-Miocene Asmari Formation consists of carbonate facies with lesser amount of evaporites. The evaporite unit deposited at the base of the Asmari Formation is called Basal Anhydrite. Depositional model was investigated using field data, geophysical logs and the Basal Anhydrite facies ...
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The Oligo-Miocene Asmari Formation consists of carbonate facies with lesser amount of evaporites. The evaporite unit deposited at the base of the Asmari Formation is called Basal Anhydrite. Depositional model was investigated using field data, geophysical logs and the Basal Anhydrite facies in the Dezful Embayment (DE). Seven microfacies were recognized in seven outcrops located in the Bangestan, Sefid, Asmari and Anaran anticlines. They were deposited in tidal flat and lagoon environments of inner ramp. Anhydrite facies is a distinct and pure evaporite unit with no carbonate components. Two main textures, fine crystalline (alabastrine) and coarse crystalline (porphyroblast), were distinguished in samples indicating replacement of anhydrite by gypsum. Gamma ray, neutron, sonic and density logs of 20 wells in 15 oilfields in the DE indicate that evaporite facies, present at the base of the Asmari Formation, is composed of anhydrite and halite. Anhydrite is present in the most of the DE wells and halite and small amount of anhydrite are present in three central wells. The results of geophysical logs and microfacies studies of the Asmari Formation reveal shallow water-shallow basin environment for the Basal Anhydrite.
