Inorganic control on original carbonate mineralogy and creation of gas reservoir of the Upper Jurassic carbonates in the Kopet-Dagh Basin, NE, Iran (original) (raw)
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The Upper Jurassic Mozduran Formation (Oxfordian-Tithonian) is the main petroleum reservoir in the Kopeh-Dagh Basin, northeast Iran which consists predominantly of carbonate rocks with subordinate evaporites and siliciclastics that were deposited in platform to deep marine settings of a subtropical sea. Detailed field surveys, petrographic investigations, facies and wire line logs analyses were carried out at eight surface sections and four wells in the Kopeh-Dagh Basin. Integration of petrographic and isotopic data suggests primary low-Mg calcite (LMC) mineralogy of Oxfordian and Tithonian ooids. On the other hand, in the wells, Kimmeridgian ooids and cements are dominantly aragonitic and high-Mg calcite mineralogy (HMC). Marine cements with isopachous, fibrous and isopachous bladed fabrics indicate original aragonite and HMC mineralogy, respectively. The domination of aragonite mineralogy could be related to increased hypersalinity, evaporite precipitation and consequently an increase in Mg/Ca ratio, which resulted in formation of aragonite in preference to calcite. Preserved ooids with radial and concentric cortices in shallow-water settings that are nearby siliciclastic source, together with aragonitic and HMC ooids accompanied by evaporites in the drilled fields, suggest original mineralogy was probably controlled by inorganically following local salinity variations. This study suggests that Kimmeridgian pay zones are mainly controlled by depositional facies, aragonitic and HMC mineralogy, and diagenetic processes such dolomitization and dissolution.
Original mineralogy of the Upper Jurassic carbonates in the Kopet-Dagh Basin , NE Iran
2011
The Kopet Dagh Basin in northeast Iran contains giant Khangiran and Gonbadli gas fields. This study deals with the main hydrocarbon reservoir of Upper Jurassic (Oxfordian-Tithonian) Mozduran Formation, which is composed mainly of limestone and dolomite, with minor amounts of marl/shale, siliciclastics and evaporites. The objective of this study is carbonate mineralogy of the Mozduran Formation. Thin sections were stained by alizarin-red S to detect dolomitization of grains and cements. Regarding diagenetic products and their diagenetic environments, selected samples were observed with a cathodoluminescent microscope (Nikon CL, CCL 8200) at the Research Institute of Petroleum Industry (R.I.P.I). Detailed field studies, petrographic investigations and facies analyses of eight surface sections and four wells, led to the recognition of several facies that define deep basin, fore-shoal, shelf margin, lagoonal, tidal flat and coastal plain facies belts, which deposited on a rimmed-shelf a...
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سیستم نشریات دانشگاه اصفهان, 2010
The Surmeh Formation with the age of Jurassic composed of shallow-water limestones and dolomites. The study area is located in the southwest of Iran in the Kohkiluyeh Province. Fluid inclusion analysis can be a good approach for studying trend diagenesis of cements in carbonate rocks. Petrographic observation of the Surmeh Formation reveals the presence of 10 different cements related to various diagenetic environments. This study attempts to determine the temperature of cement precipitation, the salinity of the fluid from which the cement precipitated and the diagenetic environments. Frequency histograms of Th (temperature of homogenization) and bivariate plot of Th and Tm ice (temperature of final ice melting) show distinct areas for each cement. Also, the petrographic observation and fluid inclusion data (Th and Tm ice) reveal that timing of precipitation of 5 types of coarse-crystalline cements in this successtion , began from meteoric diagenesis and continue to deep burial diagenesis. All of fluid inclusions exhibit two-phases (liquid-vapour phase), which the liquid ratios is more than vapour ratios. In addition, trace element and isotopic geochemistry of carbonates from different environments can be used as a powerful tool for determination of paleoenvironmental and original mineralogy of carbonates rocks. Major and minor elements and carbon and oxygen isotopes values were used to determine the original carbonate mineralogy of Surmeh Formation. In this research, petrographic evidence, elemental, oxygen and carbon isotopes values indicate that aragonite was the original carbonate mineralogy in this formation. Bivariate plot of Sr/Ca values versus Mn, also illustrate that Surmeh carbonates were affected by non-marine diagenesis in a closed to semi-closed system.
Marine and Petroleum Geology, 2021
Lithostratigraphy and biostratigraphy of Middle to Upper Jurassic carbonate platforms of the Eastern Kopet Dagh (EKD), northeastern Iran were assessed. Up to 3000 m of sedimentological logs located along ten stratigraphic sections were investigated. At least five types of carbonate production systems were identified in the study area: (1) a mud-dominated platform carbonate topped by (2) an off-platform carbonate grain-production system, (3) a grain-reworking system deposited within basinal settings (gravity-driven reworking), (4) mounds built by tubular sponges and corals, and (5) prograding oolitic wedges. The first carbonate production system (Callovianearly Oxfordian) yields platy and solitary corals, together with stromatactis-like structures. The second carbonate production system is represented by upper Oxfordian off-platform grainstones. These two carbonate production systems comprise the Khaneh Zou Fm. The third system is characterised by oncoids, originating from the carbonate platforms. These oncoids, together with bioclasts, were transported into the Kimmeridgian hemipelagic succession of the Chaman Bid Fm. The last two carbonate production systems are common in the Mozduran Fm. Tithonian tubular sponges, corals mounds, and their related dismantling products constitute a major characteristic system of the Mozduran Fm. Shallowing-upward prograding clinoforms are a second characteristic system of the Mozduran Fm., whereby ooids, generated under shallow-water conditions, were shed downslope to form interbeds within basinal mudstones. Our findings suggest that the combination of 2 nd order eustatic sea-level changes with hydrodynamic processes as well as rift-inherited morphologies and climatic changes controlled the development and lateral facies evolution of the Middle to Upper Jurassic carbonate platforms. The description of these carbonate systems and of their morphology, together with stratigraphic interpretations may lead to exploration of complex structural-stratigraphic traps, thereby highlighting new potential hydrocarbon reservoirs in the EKD.
Journal of Petroleum Geology, 2009
Upper Jurassic carbonates of the Mozduran Formation constitute the principal reservoir intervals at the giant Khangiran and Gonbadli gasfields in the Kopet Dagh Basin, NE Iran. These carbonates were investigated using detailed field studies and petrographic and wireline log analyses in order to clarify their depositional facies and sequence stratigraphy. Facies were interpreted to reflect deep basin, fore-shoal, shelf margin, lagoon, tidal flat and coastal plain depositional systems.The Mozduran Formation is composed of six depositional sequences. Thickness variations were controlled by differential subsidence. Aggradation on the platform margin and reduced carbonate production in the deep basin together with differential subsidence resulted in the creation of a narrow seaway during the late Oxfordian. Petrographic studies suggest that Mozduran Formation carbonates had a low-Mg calcite mineralogy during the Oxfordian, and an aragonite to high-Mg calcite mineralogy during the Kimmeridgian. Reservoir pay zones are located in highstand systems tracts within the lower and middle Kimmeridgian depositional sequences. The rapid lateral thickness variations of these sequences were controlled by tectonic factors, leading to compartmentalization of the Mozduran Formation reservoir with the possible creation of stratigraphic traps, especially at the Khangiran field.
Diagenetic History of the Mid-Cretaceous Carbonates in Southwestern Iran and the Persian Gulf
The Mid-Cretaceous Sarvak Formation in southern Iran and the Persian Gulf represents a carbonate ramp that developed at the north eastern edge of the Arabian Plate. The carbonate platform which records the Anoxic Oceanic Event (OAE) was periodically subaerially exposed during Cenomanian-Turonian. Regional Turonian unconformity that marked the top of these carbonates greatly influenced the diagenesis of the underlying carbonates. In this study a detailed investigation of the Sarvak Formation diagenesis were carried out in surface and subsurface sections where the effects of the unconformities were documented. A combination of petrographic and geochemical analysis is utilized to unravel the diagenetic history of the Cenomanian-Turonian carbonates in the study area. Over 300 thin sections were examined using transmitted light and over 100 representative samples studied using a Technosyn 8200 MKII model cold cathodoluminescence (CL) microscopy. Rudist's shells, calcite matrix and different types of cements were micro-sampled. Powdered samples were analyzed for stable oxygen and carbon isotopes analysis using a Finnigan Mat Delta Plus mass spectrometer. All the results for oxygen and carbon isotope analysis are reported in per mil (‰) notation relative to the Vienna Pee Dee Belemnite (VPDB) standard. Precision for both isotopes was better than 0.05‰. Trace elements data were obtained using an ICP-MS at Great lake Environmental Research institute, University of Windsor. Based on field and petrographic investigations, the most important diagenetic processes which have influenced these strata could be summarized as; dissolution, compaction, dolomitization, pyrite formation and calcite cementation. The most abundant calcite cements observed include: Drusy mosaic, blocky, equant and syntaxial from which the drusy and blocky calcite cements were sampled for geochemical analysis. The δ 13 C and δ 18 O values of the calcite matrix range from-6.4‰ to 4.1‰ and-9.4 to-0.9‰, and drusy mosaic calcite cements display values ranging from-5.8 ‰ to 3.6‰ and-9.3‰ to-0.6‰ respectively. In blocky calcite cements the δ 13 C shows values between-2.4‰ to +3.6‰ and δ 18 O from-12.3‰ to-2.8‰ VPDB. Considering the petrographic and chemical analysis results, the Mid-Cretaceous carbonates in this area went through diagenesis in variety of environments ranging from marine to meteoric and burial. Although the results of the δ 13 C analysis of most of the drusy mosaic and blocky calcite cements indicate the marine origin and even the OAE traces in these cements, depleted δ 18 O values confirms their precipitation in mixed marine-meteoric environment. A likely mechanism that could cause δ 13 C depletion in some of drusy mosaic cements (i.e.,-5.8 ‰) is meteoric diagenesis associated with oscillations in sea level (mainly the Cenomanian-Turonian and mid Turonian sea-level fall) that episodically exposed these shallow-water carbonates. Low concentrations of Sr (= 59 ppm) in these cements could also confirm the influence of meteoric waters on them. Higher depletion of δ 18 O values (i.e.-12.3 ‰ VPDB) and two-phase fluid inclusions in some blocky calcite cements suggest their precipitation at higher temperatures in burial environment.
Himalayan Geology, 2019
The Lower Cretaceous carbonates succession (Shurijeh and Tirgan formations) in west Kopet-Dagh basin (NE-Iran) was examined to study the diagenetic modifications. Various diagenetic processes were controlled by the original facies characteristics, carbonate mineralogy, climatic condition, sea-level fluctuations and burial history.Four types of dolomite are identified including 1: microcrystalline matrix replacement dolomite (xenotopic, D1), 2: fine to medium euhedral-to subhedral crystalline matrix replacement dolomite (D2e), 3: fine to medium euhedral-to subhedral porphyrotopic crystalline matrix replacement dolomite (D2p), and 4: fracture filling, euhedralto subhedral dolomite (D3). All dolomite samples were analyzed for carbon and oxygen stable isotopes. The microcrystalline dolomites (xenotopic, D1) define a relatively wide range of δ O values from 0.3 to-4.52‰V-PDB (pee dee belemnite), and narrower range of δ C l8 l3 values from 1.96 to 3.20‰V-PDB, which are slightly depleted compared with the original isotopic signatures for the Lower Cretaceous marine dolomites. The planar-e dolomites (fine crystals) in the matrix show δ O and δ C values ranging from-l8 l3 2.17 to-5.33‰ and 3.20 to 3.50‰ V-PDB respectively. Dolomitized orbitolinid and euhedral mosaic dolomite crystals with planar boundaries (D2e, medium crystals) show depleted δ O and δ C values ranging from-8.12 to-4.11‰ and 0.3 to l8 l3 3.34‰ V-PDB respectively. Fine crystal dolomites (D2e) formed during early burial and could be considered as recrystallized forms of D1 dolomite. Fluids responsible for the formation of medium crystals dolomites (D2e, medium) and orbitolinid filled dolomite (D2e), suffered higher temperature due to increasing the burial depth. Consequently, heavier δ O l8 values of finer dolomite crystals and elevated temperatures to lighter δ O values indicate in higher burial depths that led to l8 coarser euhedral crystals during dolomitization.
Carbonates and Evaporites, 2010
The Upper Jurassic Mozduran Formation with a thickness of 420 m at the type locality is the most important gas-bearing reservoir in NE Iran. It is mainly composed of limestone, dolostone with shale and gypsum interbeds that grade into coarser siliciclastics in the easternmost part of the basin. Eight stratigraphic sections were studied in detail in south of the Agh-Darband area. These analyses suggest that four carbonate facies associations and three siliciclastic lithofacies were deposited in shallow marine to shoreline environments, respectively. Cementation, compaction, dissolution, micritization, neomorphism, hematitization, dolomitization and fracturing are diagenetic processes that affected these sediments. Stable isotope variations of d 18 O and d 13 C in carbonate rocks show two different trends. High depletion of d 18 O and low variation of d 13 C probably reflect increasing temperatures during burial diagenesis, while the higher depletion in carbon isotope values with low variations in oxygen isotopes are related to fresh water flushing during meteoric diagenesis. Negative values of carbon isotopes may have also resulted from organic matter alteration during penetration of meteoric water. Fe and Mn enrichment with depletion of d 18 O also supports the contention that alteration associated with higher depletion in carbon isotope values with low variations in oxygen isotopes took place during meteoric diagenesis. The presence of bright luminescence indicates redox conditions during precipitation of calcite cement.
In the Getic of the Carpatho-Balcanides (eastern Serbia) and the Tirgan Formation of the Kopet-Dagh Basin (northeast Iran), platform carbonates were deposited during the Barremian/Early Aptian in environments in the domain of the northern Alpine Tethys and deformed during the Alpine orogeny. In this study, Urgonian carbonate platform deposits are discussed in detail with regard to depositional facies, microfacies, biostratigraphy, palaeoenvironments and palaeoecology. Detailed sedimentological and palaeontological investigations have been carried out on five sections in eastern Serbia and three sections in northeast Iran supported by an analysis of 392 thin-sections. Petrographic analysis of thin-sections led to the recognition of eight microfacies types grouped into four facies zones. A supratidaleintertidal (restricted)eintertidal (open-lagoon)eplatform-margin sand-shoal transition was recorded in both areas. Supratidal facies are characterized by bioclastic mudstones and fenestral and peloidal wackestones and packstones; intertidal (restricted) facies are represented by bioclastic wackestones, whereas intertidal (open-lagoon) facies are indicated by bioclastic packstones/grainstones and oncoid grainstones. High-energy sand-shoal facies are dominated by ooid grainstones/rudstones followed by orbitolinid packstones. Benthic foraminifera are especially abundant and along with calcareous algae are the most important fossils used for age determination of shallow-marine carbonate deposits. Thirty-two benthic foraminiferal genera were identified from eastern Serbia with an additional 38 genera from northeast Iran dominated by agglutinated forms. Identified calcareous algae provide significant data for depositional environments and palaeoecology. The microfossil associations in the two regions are very similar and share a number of common characteristics, but also some differences and show a strong affinity to those of the northern margins of Tethys. In both study areas shallow-marine environments of the Barremian/Early Aptian were replaced by deep-marine conditions during the Late Cretaceous.