جستجوی مقالات مرتبط با کلیدواژه « دیاژنز » در نشریات گروه « زمین شناسی »

In this study, Shahbazan Formation has been studied from the perspective of diagenetic processes and paragenetic sequences. This formation extends to the middle to late Eocene age in a large area of Lorestan sedimentary basin. In this area, a 62-meter-thick surface section has been selected in 10 km northwest of Poldokhtar city. Shahbazan Formation in the study area is located on the Kashkan detrital Formation and is covered by carbonates of Asmari Formation as a continuous discontinuity. Petrographic studies have been performed on thin sections and SEM studies have been performed on 10 samples of dolomites. Petrographic studies led to the identification of several diagenetic processes such as micritization, neomorphism, cementation, compaction, dissolution and replacement, which finally determined the diagenetic model. Based on the petrographic evidence, the paragenetic sequence of the Shahbazan Formation deposits in this section has been interpreted in four marine environments, freshwater, burial and uplift, and during three stages of diagenesis, namely primary diagenesis (Eogenetic), middle diagenesis (Mesogenetic) and late diagenesis (Telogenetic) has been determined. The most important diagenetic process in the studied section is dolomitization, which is formed both primary and secondary. Primary dolomites have low amounts of Fe and high amounts of Sr and Na, while secondary dolomites have high concentrations of Fe and lower amounts of Sr than primary dolomites, indicating a diagenetic burial environment. Shallow to medium for secondary dolomites.

Shahbazan Formation is one of the Eocene carbonate units of Lorestan region. In present study, dolomitization models this formation were investigated by petrographic and geochemical (EDS) methods. The section under study is 71 m in the thickness and located at 65 km southwest of Khorramabad including carbonate and dolomitic carbonate rocks, and dolomite. The dolomites based on the texture are categorized into dolomicrite, dolomicrosparite, dolosparite, and filling of fractures, which except dolomicrite, the others are secondary. Dolomites of first type represent the formation in the tidal zone environment. In most cases, these dolomites are seen at the end of upwardly shallowing sequences, which indicate a drop in sea level. The secondary dolomites were formed in a shallow to medium burial digenesis environment as a result of seepage of evaporated basin floor sediments into the carbonate platform of the Shahbazan Formation. Low amounts of Fe and high amounts of Sr and Na in dolomicrites, high concentration of Fe and Mn in dolomicrosparites and doloasparites along with evidences such as algal laminae, intraclasts, fenestral porosity and absence of evaporate minerals indicate the formation of this dolomite from the model of tidal, seepage and the following shallow to medium burial. Low values of Sr and high concentration of Fe and Mn in coarse crystal dolomites can indicate the increase in the size of dolomite crystals and their recrystallization during burial. The absence of saddle dolomites probably indicates the non-interference of hydrothermal solutions and fluids during the process of dolomitization of Shahbazan Formation carbonates.

A large part of the hydrocarbons of the Abadan plain region is located in the Bangestan Group, including the Ilam Formation. Ilam Formation of Santonian age is considered as one of the important oil reservoirs of Abadan plain, whose upper boundary is conformable with Gurpi Formation and its lower boundary with Laffan Formation, and it is mainly composed of limestone with regular layering and between thin layers of shale. The purpose of this study is to determine the role of microfacies and influential diagenetic processes in the reservoir part of Ilam Formation. Petrographic studies on the number of 142 thin section samples related to the drilling debris led to the identification of 7 microfacies related to the three belts of lagoon, Shoal and open marine facies. Among the most important diagenetic processes of Ilam Formation, we can mention cementation, micriteization, compaction, dolomitization, Hematization, glauconitization, pyritization, dissolution, and various types of porosity. In general, the results relating the distribution of reservoir characteristics of Ilam Formation with the study of sedimentary microfacies and influential diagenetic processes show that the best reservoir prone microfacies are wackestone to bioclast packstone and wackestone containing planktonic foraminifera. Also, among the effective diagenetic processes in the reservoir section, we can mention the dissolution and resulting porosity (vuggy porosity), porosity resulting from fracture, recrystallization (caused by microscopic porosity) and dolomitization.

In this study, based on petrographic studies, 200 thin sections, field observations, thick changes of the constituent layers, color, genus of the layers, and the size of the sediments, resulted in the identification of 5 units of rocks (unit 1 joint between the Pabdah and Asmari Formations) and 13 sedimentary micro-facies in the diametration of Asmari Formation (Sartang) have been identified. According to biostratigraphy studies, the Asmari Formation in the Sar Tang section is late Rupelian-Aquitanian in age. The gradual change of facies, the absence of turbidite deposits and the reef belt indicate the deposition of the Asmari structure on a shallow carbonate platform overnight (hemoclinical). The results in the study of Asmari Formation indicate that in the lower parts, the texture of most rocks is wackestone and packstone limestone. In the middle section, limestones with grainstone, boundstone and floatestone-rudstone textures containing corals and algae can be seen. Limestone with grainstone texture are mainly distributed in the upper part of the Asmari Formation, which has been significantly reduced due to extensive cementation, voids and porosity. According to the petrographic examination, the main diagenetic processes of the Asmari Formation are bioturbation, micritization, cementation, compaction, dissolution, neomorphism and dolomitization. Generally, sediments of Asmari Formation in the studied sequences have experienced a wide range of diagenetic processes related to different diagenetic environments (marine, meteoric and burial). The dissolution with corrosion and elimination in successions has caused the formation of dissolution porosities (such as intraparticle, inetrparticle, vuggy and moldic porosity). Dolomites are seen as shaped euhedral, rhombus and mosaics of the same size, dense and with subhedral and anhedral borders (dolomicrosprite and rhombus dolomite).

The Sarvak formation (Cenomanian-Turonian) has one of the main stratigraphical units in SW of Iran oil fields and Abadan plain due to huge amounts of trapped oil. Investigation of Sarvak Formation based on 3 wells data including core, petrographical analysis, petrophysical logs, and POROPERM data which was received from the core laboratory, led to recognized seven microfacies in this succession. The identified facies were deposited in five sub-environments; restricted lagoon, shoal rudist biostromes, and open marine. The situation of each facies and their depositional setting proposed the homoclinal carbonate ramp platform.Petrographical investigation shows the several diagenetic realms that affected this formation. the main diagenetic process identified in this research are, micritization, mechanical and chemical compaction, dissolution, cementation, stylolitization, dolomitization, silicification, and fracture. The depositional environment of Sarvak formation affected by a sea-level change in Cenomanian-Turonian time which is affected the reservoir section by several diagenetic phenomena. To investigate the reservoir rock typing two methods were analyzed. One of them is based on microfacies analysis and diagenetic process investigation and the other is based on RQI/FZI index. integration data and analysis show that dissolution has a positive effect, especially in grain-supported facies and cementation has a negative impact on reservoir quality index. the result of this study could be implemented in the planning of hydrocarbon exploration and development stage.

The Campanian-Maastrichtian sequence in the Shiraz region of Inner Fars includes Gurpi and Tarbur formations. In order to study petrography and evaluate the evolution of the sedimentary environment and sequence stratigraphy of these sediments, two stratigraphic sections of Koh-e Qhale and Koh-e Shahrek Abarj in Marvdasht city of Fars province were selected and analyzed. Based on field studies, manual samples, and a detailed microscopic study of 250 thin sections prepared from the studied formations, it was identified that 14 facies (11 carbonate microfacies and three lithofacies) were deposited in a shelf carbonate platform. By studying about 1400 meters of Maastrichtian sediments, depending on the location of the sections under study, three third depositional sequences were identified and separated in terms of sequence stratigraphy. During the Campanian period and the formation of the LST systems tract towards the northeast of the studied area (Koh-e Qhale section), the clastic sediments of the lower part of the Tarbur formation and in the deeper parts of the sedimentary basin of the Gurpi formation were deposited equivalently. At the time of the highstand systems tract (HST facies) and high carbonate production rate in the steep part of the sedimentary environment, interlayered reef deposits (rudist packstone and rudist grainstone) were deposited between the limestones of the Tarbur Formation.

Diagenetic processes in carbonate rocks can be considered as one of the most important factors influencing the inherent characteristics of this type of reservoir on a small as well as large scale. Considering the importance of knowing the mechanical characteristics of reservoir rocks in geomechanical modeling and its application in the exploitation and development of hydrocarbon fields, it is necessary to find out how lithological characteristics affect its rock mechanical behavior. In this study, the impact of two diagenetic processes (Dolomitization and Anhydrite cement) on the physical and mechanical characteristics (such as Uniaxial Compressive Strength, Young’s modulus, Cohesion, and Internal friction angle) of carbonate reservoirs of the Kangan Formation, are addressed. The evaluations have been done in two phases: i.e., lithological studies and rock mechanical tests. The results show that changes in mechanical properties are strongly influenced by diagenetic processes. The two main influential features on mechanical characteristics are dolomitization and anhydrite cementation, which strongly affect porosity, dominant pore type, and mineralogy. The results show that dolomitization in the studied samples has caused an increase in porosity and a decrease in strength and elasticity. While the presence of anhydrite has caused an improvement in the resistance characteristics with an opposite effect.

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 .

The Kopeh Dagh sedimentary basin is an intercontinental basin formed following the closure of the Paleo-tethys ocean due to a collision between the two continents of Iran and Turan and in has arisen the Early Cimmerian orogenic phase. Deposition of shallow carbonates during the Lower Cretaceous (Barmin-Apsin) in the Kopet Dagh sedimentary basin has been introduced as the Tirgan Formation. This formation is located in three studied sections on the Shurijeh detrital siliceous formation and below the limestone-marni formation of Sarcheshmeh.

In this research, this formation uses petrographic studies and geochemical analyzes to evaluate the sedimentary model, primary carbonate mineralogy and diagenetic processes in Shirvan (197.7 m), Quchan (464.4 m) and Chenaran (127.8) sections. 720 thin sections were prepared for petrographic studies. To separate ferroan calcite and dolomite from nonferroan samples, the samples were stained with potassium ferrocyanide solution (Dickson, 1996). In order to name carbonate rocks, the method (Dunham, 1962) and detrital rocks, classification (Folk, 1980) were used. The method (Flugel, 2010) was also used to interpret the facies and present the sedimentary model. For geochemical studies, 41 samples were analyzed by ICP-OES method in Iran-Karaj Mineral Processing Research Center (Emidro Company) for elemental analysis and by ICP-MS method in Science Laboratory Center of Ottawa University of Canada for carbon isotope and oxygen.

Petrographic studies led to the identification of 18 microfacies that were deposited in four facies belts open marin, lagoon, Barrier and tidal flat. The frequency of tidal facies along with barrier facies and the absence of large reef barrier and turbidite sediments indicate the deposition of this formation in a ramp system with a carbonate slope. Diagenetic processes in this formation include: cementation, micritization, dissolution, compaction, dolomitization, fracture, stylolitification and silicification. The abundance of skeletal and non-skeletal components of calcite along with calcite cement, abundance and presence of dolomite with high content of stransiom refers to the initial mineralization of calcite in the carbonates of Tirgan Formation in time. Also, the values ​​of major (Mg, Ca) and minor elements (Sr, Na, Mn, Fe) and the isotopic range of oxygen 18 and carbon 13 of the limestones of Tirgan Formation, also indicate the composition of primary calcite mineralogy in these areas. This value also shows the impact of the burial diagenesis environment on these deposits in a semi-closed diagenesis system with a low water-to-rock ratio. The average diagenetic temperature of seawater at the time of sedimentation of carbonates of Tirgan Formation using the heaviest oxygen isotope in calcareous samples is estimated to be 18.21 ° C.

Comparison of the data obtained from the three studied sections and the information provided from the eastern and western regions, shows an increase in temperature and thus an increase in strontium to the west, which it is indicates a change in the mineralogical composition from calcite to aragonite from east to west basin

Shurijeh Formation (Neocomian - Barremian) is the main hydrocarbon reservoir in north east Iran. Most gas reservoir production place in zones B and D of this formation. In this study, comprehensive petrographic and petrophysical studies were performed to understand the factors controlling the reservoir quality of this formation. With respect to the petrographic studies, well log data, evidence achieved from the core and drill cuttings, five primary facies (petrofacies), including microconglomerate, sandstone, claystone/shale, sandy dolomudstone, and dolomitic- sandy dolomitic ooid grainstone / hybrid, were identified in the deposits of Shurijeh Formation. Sedimentary facies of the Early Cretaceous reservoir in the studied wells belong to the upper part of the supratidal zone, intertidal zone, lagoon, braided river (longitudinal bars) and meandering river (flood plain and oxbow lake). In this study, based on porosity and permeability data, 4 units of Hydraulic flow units (HFUs) were identified using flow zone indicator (FZI) method. The results of this study showed that the diagenetic processes like dissolution, dolomitization and chemical compaction (stylolites and dissolved vein) are related to the grain supported facies including micro-conglomerate, sandstone and dolomitic- sandy dolomitic ooid grainstone / hybrid and hydraulic flow units (HFU4) and hydraulic flow unit (HFU3) that have the best reservoir quality are connected. The results of this study showed that the diagenetic processes like dissolution, dolomitization and pressure dissolution (stylolites and dissolved vein) are related to the grain supported facies including micro-conglomerate, sandstone and dolomitic- sandy dolomitic ooid grainstone / hybrid and hydraulic flow units 4 and 3 that have the best reservoir quality are connected. Diagenetic processes of cementation (Silica, carbonate and anhydrite) and alteration of feldspars are associated with the dominant mud facies including claystone/shale, sandy dolomudstone of hydraulic flow units 2 and 1 which have the lowest reservoir quality.

This research is based on sedimentological study of 4 surface (Kabir kuh, Samand, Anjir and Anaran) and 8 subsurface wells in the Lurestan, North Dezful and Abadan plain with a total thickness of 1592 m. The Santonian – Lower Campanian Ilam Formation is a carbonate hydrocarbon reservoir in the Zagros fold – thrust belt, in SW Iran. Twenty microfacies were recognized based on microscopic study. Microfacies analysis led to the recognition of four facies belts including inner (shoal), mid, outer ramp, and basinal setting. Correlation of depositional environments together with lateral facies changes indicate deposition are distally steepend ramp. Deep marine and inner ramp facies are the most and least facies, respectively in the study area. As the distribution of inner ramp facies is very limited, it can only be recognized in wells from North Dezful and Abadan plain.The results obtained from facies together with analyses of wireline logs clearly shows a northward deepending of the depositional environment from Balarud Fault. Cementation, micritization, compaction, solution seams, neomorphism, disolution, fracturing, pyritization, phosphatization, gluconitization and bioturbation are the main diagentic processes. However, cementation is most dominant in shallow marine facies in the Abadan plain, whereas, pyritization, stylolite and fracture are the most prevailing processes in deeper marine facies of the Ilam Formation in Lurestan. There is a limited distribution of porosity, but the most dominant types are, interpartical, microporosity and fracture related porosity. The Ilam carbonates are mostly affected by shallow to deep burial diagenesis in Lurestan,

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.

The Sarvak Formation, with a total thickness of 1566 m and major limestone lithology in the Ahvaz and Mansouri oil fields, is studied to determine its palaeoenvironment, diagenetic overprint and geochemistry. In the studied wells, the formation conformably overlies the Kazhdumi Formation and is overlain by the Ilam Formation. The petrographical studies led to identifying twelve facies precipitated in four major sub-environments, including inner-, middle-, and outer ramp and an intra-shelf basin on a homoclinal ramp-type setting. Dissolution, compaction, and cementation are the main diagenetic alterations that changed the primary chemical composition and the reservoir property of the Sarvak Formation. These diagenetic processes occurred in phreatic marine, meteoric, and burial realms. Sedimentary geochemistry of major and trace elements, including Ca, Mg, Fe, Mn, and Sr, along with O and C stable isotopes, reveal aragonite as the original carbonate mineralogy of the Sarvak Formation. The depositional environment in the lower Sarvak with the predominant shallow open marine and stratigraphic succession with no evidence of exposure, change to stratigraphic succession with more shallow sub-environments (lagoon and bioclastic-shoal), and the evidence of exposure such as cementation and extensive dissolution, which led to depletion in Sr, δ18O, and δ13C and enrichment in Fe and Mn during sea level fall in the inner ramp microfacies. The Fe and Mn cross-plot with a positive trend shows the effects of diagenetic phases in minor phreatic marine and mainly meteoric realm, all confirmed by petrography. The Sr/Ca ratio has the most correlation to the modern tropical warm-water shallow marine that could confirm the primary aragonite mineralogy; which is supported by the predominance of carbonate mud in the identified facies, primary isopachous fibrous marine cements, and extensive dissolution evidence. The cross-plot of Fe versus Sr and Mn versus Sr/Mn ratio suggests deposition in mainly an oxygenation state that experienced low to high water/rock interaction during different depositional sequences. The δ18O and δ13C co-variation and their comparison with the other fields of the Sarvak conducted in different regions show precipitation in an isotopic equilibrium in the carbonates with the Upper Cretaceous seawater, since calculating salinity (Z=130) and temperature (T= 26°C) of the Sarvak Formation confirm the above statement.

Jahrom and Asmari Formations in two wells from Nargesi field in the southern part of Dezful Embayment were studied to interpret the sedimentation and diagenesis history of Paleocene-Miocene successions. A total of 14 different microfacies were identified based on the study of 270 m drilling core and 495 microscopic thin sections,which are located in four sets of open marine, shoal, lagoons and tidal flats. The microfacies of the Asmari Formation are include tidal and lagoon sets. The microfacies of the Jahrom Formation are include middle ramp and the open marine, and energetic facies of the shoal sets have been observed in abundance in this formation, and to a lesser extent has lagoon facies. According to the characteristics of the above microsfacies, it is suggested that a shallow carbonate ramp with a gentle slope be used as a sedimentation environment for these Formations in Nargesi field. Asmari Formation is deposited in the shallower parts of this ramp. The paragenetic succession of Jahrom and Asmari Formations has been interpreted based on petrographic evidence in four marine, meteoric, burial and uplifting environments, and have affected sediments, during the three stages of eogenesis, mesogenesis and telogenesis. Dolomitization, cementation, anhydritization, micriticization, neomorphism, compaction, dissolution and fracture are the predominant diagenetic processes in these Formations. Dolomitization and anhydritization processes have been observed throughout the Asmari Formation, but are less intense in the Jahrom Formation. Asmari Formation cements are mostly dolomitic and anhydrite, but Jahrom Formation cements are mostly calcite.

In order to understand the sedimentation history of carbonate rocks of Asmari Formation, a 145 m thick stratigraphic section was selected in the south of Lorestan. The lithology of this periodic formation is from thin-layer, middle-layer limestones, thick to very thick-layered. The samples taken from this section are 145 samples that were examined in terms of sedimentary environment and diagenetic processes based on field evidence and studies of thin microscopic sections and due to the absence of evidence such as the construction of bird eyes. , Stromatactis cavities, Typical structures, Intracellular components, Evaporative minerals and the absence of traces and structures resulting from sediment drying as well as the absence of slippery and sedimentary sediments (turbidites, intraclasts and sections) Finally, it led to the identification of 7 micro-defects related to 4 lagoon facies belts, dam, restricted section (middle ramp) and internal ramp. In this section, several diagenetic processes such as micriticization, morphology (increasing and decreasing), cementation (coaxial cement, fibrous thickness, dimensional, block, joint and kilotopic dynamics), compaction (mechanical and chemical), dissolution (dependent To fabric and non-fabric dependent), substitution (pyritization, silicification and dolomitization) and diagenetic modeling. Based on petrographic evidence, the paragenetic sequence of Asmari Formation deposits in this section has been interpreted in four marine environments, freshwater, burial and uplift. Three stages of diagenesis, namely primary diagenesis (eogenesis), middle diagenesis (mesogenesis) and final diagenesis (telogenesis) have been determined for the studied deposits.

In northern region of Khorramabad city in Lurestan province, Asmari Formation is mainly composed of limestone with some interbeds of marl. The studied Formation, is late Oligocene-Early Miocene in age. In this study, petrographic studies as well as stable isotopes of oxygen and carbon have been used to make an understanding of after sedimentation conditions. We also have identified and distinguished some evidence from each diagenetic stage. Consideration of the cements, which have been deposited in cavities and fractures of carbonate rocks shows that sometimes there are differences in the isotopic oxygen content and carbon content of the edge and central parts. However, these changes in many cases are slight. Numerous diagenetic processes such as calcite cementation (syntaxial overgrowth cement, isopachous fibrous, spar mosaic cement, blocky cement, and granular cement), iron oxide cement, pyrite, limited dolomitization, micritiization, bioturbation, fractures and fillings and dissolution, incremental neomorphism, physical and chemical compaction (stylolite and stilomotel) have been affected the limestone successions of Asmari Formation in the study area. Some of these processes may occur in several diagenetic environments. In order to differentiate them, we have used cathodoluminescence and isotope study techniques. We have been utilized the oxygen and carbon stable isotopes track each diagenetic phase. In this study, we have used cathodoluminescence images to make a map for isotopic analysis. Finally, by integrating petrographic, cathoduminescence, and isotopic data, different diagenetic environments have been identified and distinguished. We hope this information make a more accurate picture of after sedimentation conditions of the sedimentary Basin.

The Sarvak Formation was deposited on shallow-marine carbonate platforms under the controls of tectonic and eustatic changes during the Upper Cretaceous in the Zagros area. It forms on of the most important reservoir intervals in SW Iran. Complex depositional setting and diagenesis history have resulted in a heterogeneous carbonate reservoir. This study, integrates the results of petrographic (facies and diagenesis) studies with petrophysical and reservoir data (core porosity-permeability and wireline logs) to evaluate the controls of depositional and diagenetic processes on the distribution of reservoir quality in the Sarvak Formation. Ten hydraulic flow units are determined using the FZI concept. Twelve reservoir and non-reservoir (baffle and barrier) units are identified using the Lorenz approach. Finally, dominant depositional facies and diagenetic alterations are evaluated in each HFU and reservoir zone. Results of this study showed that meteorically-dissolved rudist-dominated facies and high-energy facies of shoal complexes formed the best reservoir units in the Sarvak Formation. In sequence stratigraphic point of view, these zones are located in the RSTs of third-order sequences, beneath the disconformity (paleoexposure) surfaces. In contrast, the compacted and cemented mud-dominated facies concentrated in the TSTs and around the maximum flooding surfaces (MFS) formed the non-reservoir units of the Sarvak Formation.

The Lower Cretaceous Fahliyan Formation is one of the main oil reservoirs in the Persian Gulf. In this study, for investigating facies characteristics, depositional environment, diagenetic features, sequence stratigraphy and describing factors controlling reservoir quality, the integration of the results from core description, petrographic studies, and petrophysical data was utilized. Nine main facies were recognized and grouped in four facies belts of lagoon, shoal, patch reef and shallow open marine, indicating deposition of the formation in a carbonate ramp platform. Various diagenetic processes that influenced facies, occurred in marine, meteoric, and burial diagenetic realms. Four main pore types have been identified in the reservoir that include interparticle, moldic, vuggy, and microporosity. From the sequence stratigraphy point of view, three third-order sequences which are correlatable within the Fahliyan Formation were identified. The development of grainstone and algal rudstone/floatstone in shoal/ patch reef sub-environment played an important role in developing the high reservoir. In view of their controls on reservoir quality and pore system, diagenetic features can be categorized into two classes: (1) diagenetic processes enhancing reservoir quality that include dissolution and fracturing, and (2) diagenetic processes reducing reservoir quality that include cementation and compaction.

In this study, the Late Paleocene Taleh Zang Formation in the southwest of Kermanshah hasbeeninvestigatedfor elemental geochemistry and effective diagenetic processes during burial. The thickness of the studied section is 282 meters that mainly composed of shallow marine limestones with interbedded of marl and dolomite. The main diagenetic processes affecting the TalehZangFormation include micritization, various types of porosity, cementation, dolomitization and compaction. Due to the texture and the abundance of unstable skeletal particles (green algae and bivalve), porosity and cementation aremorecommon among the identified processes. Microscopic and geochemical studies have shown that these processes have taken place in eogenesis and early mesogenesis stages in marine, meteoric and shallow burial environments. Evidences indicate that the carbonates of the TalehZangFormation didnot tolerate deep burial after the deposition during diagenesis. Fluids that affected the lower parts of the formation during burial were mainly marine. Moreover, tothetop ofthe sequence in addition to seawater less meteoric fluids have affected the marine carbonates of the Taleh Zang Formation during diagenesis. The high amounts of Sr/Mn (mean27/51) and Sr/Ca (mean 1/61) and also low Mn (mean 27ppm) and Fe (mean 78ppm) values indicate close digenetic system with low water/rock interaction for the carbonate samples of the TalehZangFormation.