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.
Petroleum geology
ayeshah salmani; Hossain Rahimpour-Bonab; Mohsen Ranjbaran; Seyed Mohsen Aleali
Abstract
Asmari Formation (Oligocene - Miocene) is the first fractured proliferous carbonate reservoir that ever known in the world and is the most important hydrocarbon reservoir in Iran. The large quantity of the produced oil in Dezful Embayment is from this formation. Thin section studies in this formation ...
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Asmari Formation (Oligocene - Miocene) is the first fractured proliferous carbonate reservoir that ever known in the world and is the most important hydrocarbon reservoir in Iran. The large quantity of the produced oil in Dezful Embayment is from this formation. Thin section studies in this formation lead to identification of eight microfacies related to the homoclinal ramp with three subdivisions (inner ramp, middle ramp and outer ramp). Many diagenetic processes such as; micritization, neomorphism, bioturbation, dolomitization, dissolution, cementation, mechanical and chemical compaction, fracturing have affected the Asmari carbonates in studied oil field during eogenesis, mesogenesis and telogenesis processes. Three sequences (third order) have been identified based on sequence stratigraphy studies. Based on all results from this study it could be pointed out that; dolomitization, dissolution and cementation are the most important factors that controlled the reservoir quality in this field. Cementation (calcite and anhydrite cements with different fabrics) reduced reservoir quality in different facies. Seemingly, fabric destructive dolomitization increased reservoir quality with creating intercrystaline porosity in mudstone facies and connecting isolated pores (via dissolution) in most of facies. Dissulotion has prime importance where occurred and increased reservoir quality. Contrasting to the other Asmari hydrocarbon fields in Zagros which fracturing is the most important factor in increasing reservoir quality, in Naft-Safid oil field, most of fractures have been filled by calcite cement. Thus, diagenetic imprints (such as dissolution and dolomitization) have more effects on increasing reservoir quality than fracturing.
Stratigraphy and Palaeontology
Mohammad Lorstani; Abdolhosein kangazian; Amrolah Safari; M.R Noura
Abstract
In this study, the subsurface sedimentary successions of the Asmari Formation have been studied using cores and thin sections obtained from the well no. 28 of Haftkel and correlated with well no. 186 of Masjed-I-Soleiman oilfields data. in this study,18 carbonate and 1 carbonate/evaporate microfacies ...
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In this study, the subsurface sedimentary successions of the Asmari Formation have been studied using cores and thin sections obtained from the well no. 28 of Haftkel and correlated with well no. 186 of Masjed-I-Soleiman oilfields data. in this study,18 carbonate and 1 carbonate/evaporate microfacies and 2 noncarbonated microscopic facies were recognized. These microfacies and microscopic facies were grouped in 6 facies associations (include: Tidal Flat, Lagoon, Bar, Restricted marine, Open marine, and Mid ramp). Obtained facies associations, comparing them with standard facies models and statistical analyses, indicate that Asmari Formation was deposited in the inner and middle of a homoclinal carbonate ramp. Correlating Asmari association facies in Haftkel and Masjed-I-Soleiman oilfields showed that Haftkel oilfield has been in the shore-ward and Masjed-I-Soleiman oilfield has been in sea-ward of that ramp. Sequence stratigraphy studies express that the succession of Haftkel oilfield could be discriminated to six third order deposition sequences (Sq1- Sq6). Incorporation of the sequence stratigraphy criteria of Asmari successions in this oilfield with its previous biostratigraphy data reviles that Sq1 and Sq2 occurred during Aquitanian time and Sq3 to Sq6 during Burdigalian age. Correlating of Asmari sequences of this oilfield with the Asmari sequences of Masjed-I-Soleiman, based on cyclostratigraphy data, show the sequences of Masjed-I-Soleiman occurred in Burdigalian time. Also the correlation expresses the steep of proposed ramp was toward Masjed-I-Soleiman area. The sequence correlation with global sea level fluctuations shows Burdigalian depositional sequences occurred based on eustasy in these oilfields.