List of Articles Diagenesis

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  1 - Factors controlling different types of anhydrite textures and their relation to reservoir quality in the Asmari reservoir in Ahvaz oil field
  نسترن  آزادبخت
  Various diagenetic processes have affected reservoir quality of the Asmari Formation in Ahvaz Oil Field in wells No. 19 with a thickness of 357 meters. It is composed of limestone dolomite, dolomitic limestone, sandy dolomitic limestone, sandstone, siltstone and sha More

  Various diagenetic processes have affected reservoir quality of the Asmari Formation in Ahvaz Oil Field in wells No. 19 with a thickness of 357 meters. It is composed of limestone dolomite, dolomitic limestone, sandy dolomitic limestone, sandstone, siltstone and shale. Study of 1100 thin sections from available cores at this well as well as the well’s numeral data, porosity and permeability of cores, indicates that the most important diagenetic processes is anhydritic cement with different types of textures. It appears as poikilotopic, porefilling and pervasive, nodular, fracture filling, sparce crystals, and evaporite veins. During different steps of diagenesis, these texture show replacement and pore filling porosity that have affected different facies to some degrees. Results of this study show that anhydrite cement occurs mainly in dolomitic and sandstone facies and to some extent, affected the reservoir quality. This is due to the effect of sulphate rich brines during dolomitization. Where the presence of anhydrite cements in limestone facies is sparse and rare, it has little effect on reservoir quality. However, pore filling and pervasive anhydrite texture filling all pore-space in dolograinstone and dolopackstone grain-supported facies during shallow burial intensively reduced reservoir quality. Dissolution of cements at later stage of diagenetic processes (creating secondary porosity) improved reservoir quality. In addition, solution of texture poikilotopic anhydrite in sandstone facies and repercipitated as patchy anhydrite with poikilotopic texture, results in reduction of porosity but it doesn’t make any changes in throat pores. Hence patchy anhydrite with poikilotopic texture that reduces porosity converts the sample from Lucias class 2 to class 1. Manuscript profile
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  2 - The impact of microfacies and diagenesis characteristics on the reservoir quality of Asmari Formation in the Gevarzin gas field, Zagros basin, south Iran
  Karim  Mombani   Ahmad Yahyaei
  Asmari Formation from the Gavarzin gas field have erosional unconformity boundary on marl and pelagic limestones of Pabdeh Formation and gradually change to evaporate cap rock of Gachsaran Formation. Cores studies from the one of wells of Gavarzin field is 183 m in thic More

  Asmari Formation from the Gavarzin gas field have erosional unconformity boundary on marl and pelagic limestones of Pabdeh Formation and gradually change to evaporate cap rock of Gachsaran Formation. Cores studies from the one of wells of Gavarzin field is 183 m in thickness, which includes 1.30 m from the top of Pabdeh, 162.4 m from the Asmari Formation and 19.30 m from the base layers of Gachsaran. Asmari Formation includes alternation of limestone, calcite dolomitic, claystone and shale with green marl. Petrology and facies analysis of the sequence of these formations identified 12 microfacies, a carbonate ramp from deep-sea to sabkha environments and formed in a retrograded sequence. This ramp includes deep environments, open sea, patch reef, bio-, clastic-bars, lagoon and tidal environments, which confirms a changing environment due to rapid facies changes and deposition of evaporative sediments in Gachsaran as a restricted environment. Diagenesis processes are considered as the main factors in carbonate reservoir quality of Gavarzin field. The diagenesis history of the Asmari carbonates of the studied cores is summarized as A) marine phreatic diagenesis, bioturbation, micritization and cementation processes occurred. B) vadose zone diagenesis, where the crystallization, cementation, and dissolution occurred. C) burial diagenesis, comprises compression-induced, pressure dissolution and fracturing are common. The microfacies show a wide varieties of reservoir characteristics and therefore a heterogeneous reservoir has been formed. Micro-fractures, however have strongly influence on the reservoir quality in the section. The simultaneous presence of dissolved spaces and fractures in the reservoir the permeability greatly increased. The best reservoir quality in the Grainstone/Packston facies are coated grains with moldic porosity that were created by the leaching of Ooid-bearing Packston lithology during the diagenesis of atmospheric waters. Manuscript profile
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  3 - Investigation of petrographical and geochemical characteristics of carbonate deposits of the Jamal Formation in the Chah-Riseh section, northeast of Isfahan
  Behrad  Zebhi Kamand محمد علی  صالحی Ezat  Heydari Ali Bahrami
  10.52547/ispg.39691.11.21.54
  The Middle Permian Jamal Formation have been investigated for sedimentological and geochemical aspects in the Chah-Riseh section, northeast Isfahan. According to the field studies the Jamal Formation with 251 m thickness divided into eight lithostratigraphic unit. Lower More

  The Middle Permian Jamal Formation have been investigated for sedimentological and geochemical aspects in the Chah-Riseh section, northeast Isfahan. According to the field studies the Jamal Formation with 251 m thickness divided into eight lithostratigraphic unit. Lower boundary of this formation with an unconformity is underlained by the Sardar Formation which belongs to the Carboniferous period and upper boundary with an unconformity reaches to the Lower Triassic Sorkh-Shale Formation. Facies and microfacies studies of the Jamal Formation led to the identification of two petrofacies and 14 carbonate microfacies. According to the recognized carbonate allochems, petrofacies and microfacies of the Jamal Formation and some evidence such as transitional microfacies changes, we can consider a depositional environment of a shallow mixed siliciclastic-carbonate ramp platform. Petrographically, four types of dolomites are recognized in the Jamal Formation. The dolomitization model for the type I dolomite is considered forming in tidal flat and burial dolomitization for types II, III and IV. Geochemical studies including major and trace elements analysis comprised of elements such as Ca, Mg, Sr, Mn and Fe. Using ratios of the elements and also by plotting some of these elements cross carbon and oxygen isotopes in various diagrams have been used in determining the original mineralogy of carbonate deposits and efficient diagenetic system on the Jamal Formation. The results indicate that the dominant diagenetic environment effected on the carbonate deposits of Jamal Formation was occurred in a semi-closed system and the original mineralogy was aragonite. Evaluation of major and trace elements contents of the four types dolomites, confirmed different characteristics of theses dolomite resembling crystal sizes in petrographic studies. Carbon and oxygen isotopes data of dolomites also defined their diagenetic situations. Manuscript profile
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  4 - The history of deposition and post-deposition and their effects on the reservoir quality of Asmari Formation in Ahvaz oilfield
  Akbar Heidari Milad Faraji Narges Shokri
  The carbonate interval of the Asmari formation along with sandstone deposits were deposited in most areas of the Zagros sedimentary Basin, including the Ahvaz area, in Oligo-Miocene. In this study, the effects of depositional and post-depositional environments on the re More

  The carbonate interval of the Asmari formation along with sandstone deposits were deposited in most areas of the Zagros sedimentary Basin, including the Ahvaz area, in Oligo-Miocene. In this study, the effects of depositional and post-depositional environments on the reservoir quality of zone A7 of the Asmari Formation in well No. 4 in Ahvaz oil field were studied. The study of the sequences of the Asmari Formation in this section led to the identification of 11 carbonate facies, one evaporite facies, one mixed carbonate-siliciclastic facies, and one siliciclastic facies. Sedimentary environments of tidal zone, lagoon, coral reef and open sea were introduced for the depositional environment of identified facies. Due to the absence of sudden changes, it seems that the studied deposits were deposited in a ramp-type carbonate platform that was influenced by siliciclastic sediments from the Zagros river systems. The immature sedimentary texture of the sandstone facies indicates the proximity of the origin of the quartz sources to the carbonate basin. Among the diagenetic processes that have affected the examined sequences, the following processes can be mentioned: micritization, cementation, neomorphism, physical and chemical compaction, dissolution, fracture development and filling, dolomitization, and anhydritization. These diagenetic processes occurred in post-depositional marine, meteoric and burial diagenetic environments. Many fractures were filled with petroleum, which indicates that fractures, along with dolomitization, chemical compaction, and fenestral pores, are among the most important post-sedimentation complications to increase reservoir quality. While cementation and anhydritization resulted in reducing the reservoir quality by closing the pore spaces . Manuscript profile