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.
S. Faramarzi; H. Rahimpour-Bonab; M. Ranjbaran
Abstract
The Sarvak Formation is one of the most important carbonate reservoirs of Iran. The main objective of this study is to evaluate reservoir quality of the formation by integration of petrographic studies and core porosity-permeability data in three key wells in a giant oilfield of the Abadan Plain, SW ...
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The Sarvak Formation is one of the most important carbonate reservoirs of Iran. The main objective of this study is to evaluate reservoir quality of the formation by integration of petrographic studies and core porosity-permeability data in three key wells in a giant oilfield of the Abadan Plain, SW Iran. Petrographic studies led to the identification of 13 microfacies that are grouped into three main facies belts including lagoon, shoal, and open marine (talus and slope) which deposited in an isolated carbonate platform. The main diagenetic processes affecting the Sarvak Formation are micritization, bioturbation, recrystallization, dissolution, cementation, physical and chemical compaction, dolomitization and silicification, along with fracturing. According to the results, the reservoir quality of the Sarvak reservoir is a function of both primary depositional facies and secondary diagenetic processes. Evaluation of impacts of depositional facies on reservoir quality indicated that the rudist-bearing intervals (especially rudist debris zones) have high reservoir quality. Dissolution and cementation are the most pervasive diagenetic processes affecting the formation, and occurred due to widespread meteoric diagenesis. Dissolution and fracturing are the chief factors that lead to the improvement of porosity-permeability, whilst calcite cementation and compaction have destructed reservoir quality of the studied interval. This study may assist better understand the geological parameters controlling reservoir quality of Sarvak Formation in the Abadan Plain oilfields.
L. Azad Shahraki; H. Rahimpour Bonab; M. Ranjbaran; A. Kangazian
Abstract
The Lower Cretaceous (Neocomian) carbonates of the Fahliyan Formation are considered as important reservoir rocks in the Zagros Basin. In this study, the sedimentary successions of this formation in Lar (620m thick) and Khami (517m thick) anticlines, located in the Izeh zone, were investigated to analyze ...
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The Lower Cretaceous (Neocomian) carbonates of the Fahliyan Formation are considered as important reservoir rocks in the Zagros Basin. In this study, the sedimentary successions of this formation in Lar (620m thick) and Khami (517m thick) anticlines, located in the Izeh zone, were investigated to analyze microfacies, depositional environment, and diagenetic phenomena. Based on petrographic studies, 16 microfacies related to five facies belts of tidal flat, lagoon, carbonate shoal, mid ramp and outer ramp were recognized. Grainstone microfacies were found more abundant in the Lar stratigraphic section than the Khami section. Lack of turbidite deposits and reefal facies, and transitional changing of the facies show that the Fahliyan Formation was deposited in a homoclinal carbonate ramp. Abundance of mud dominated facies and rarity of high energy facies (like shoal facies) show that the ramp was a leeward one. According to petrographic studies, the main diagenetic features of the carbonates were micritization, cementation, dissolution, neomorphism, compaction, fracturing, and dolomitization. Due to deposition in the photic zone and high sedimentation rate, the thickness of the Fahliyan Formation in both stratigraphic sections is considerable, but based on the drawn isopach map, the thickest succession of the formation is found in the Lar section. Therefore, the Lar area is considered as the depocenter of the Fahliyan Formation. Difference in the thickness of the Fahliyan successions of Lar and Khami, most probably, is caused by the syndepositional activity of the north-south trending basement faults (like Kazeroon fault) in the region. Also, difference in the quantity of the burial compaction of the carbonate successions (caused by facies and diagenetic differences) played a role in secondary (burial) thickness changes.
