The Asmari Formation with Oligo-Miocene in age and a carbonate-siliciclastic lithology is considered as one of the main hydrocarbon reservoirs in the Zagros Basin of Iran. In this research, with the ...target of unraveling the reservoir heterogeneity, a comprehensive rock typing was performed using all available geological and petrophysical data. The procedure for reservoir rock typing was started with the identifying of sedimentary rock types derived from the description of cored intervals and the study of thin sections from 7 cored wells. These studies led to the identifying and classification of 12 sedimentary facies related to the inner, middle, and outer parts of a carbonate ramp platform. The statistical clustering algorithms were applied using Multi-Resolution Graph-based Clustering approach on well log data, resulting in the recognition of five electrofacies (EFs). Accordingly, five hydraulic flow units (HFUs), based on the flow zone indicator method were defined in the reservoir interval. A compatible relationship between EFs and HFUs demonstrates that changes in petrophysical attributes are mainly controlled by diagenetic features. By examining special core analysis data, appropriate capillary pressure curves were correlated with the identified reservoir rock types. The methodology used in this study shows the reservoir heterogeneity in addition to primary depositional texture is controlled by the effect of diagenetic processes such as compaction, cementation, dissolution, dolomitization, and fracturing. Dolomitization, dissolution, and fracturing are the main diagenetic processes, showing significant effect on increasing and improving the reservoir quality. According to the results, among different reservoir zones of the Asmari, zones 1, 2, 3, and 4 are considered as the most favorable zones from the reservoir quality and production point of view in the studied field.
The Darquain field is located in the Abadan Plain SW Iran, which has a high potential for exploration and production of hydrocarbon resources with poorly defined petroleum systems. The goal of this ...paper is to characterize the Cretaceous source rock potential in the Darquain field. A gamma-sonic log was used as a proxy to identify probable source rock zones and to select sample depths. A total of 37 samples were analyzed by Rock-Eval, elemental, Gas Chromatography (GC) and gas chromatographymass spectrometry (GC-MS) techniques. The petroleum generation potential, as well as origin of the organic matter of samples, have been investigated. The results of this study indicate that, in the Early Cretaceous successions, there are favorable source zones in Garau, Gadvan, and Kazhdumi Formations. These source zones predominantly contain organic matter from marine origin, suggesting kerogen type II, while some samples contain terrestrial organic matters, suggesting kerogen type III. The Lower Garau zone, with 1.14 to 14.29% total organic carbon (TOC), is an excellent source rock with a fair genetic potential in the range of 2.74 and 9.5 mg/g. Elemental analysis results in the Lower Garau zone allow the classification of kerogens as high-sulfur. There are very good source zones in the Kazhdumi Formation, with fair to good genetic potential. The results of Rock-Eval and petrophysical analyses show that gamma ray data can be used as a useful tool to determine the potential source zones, although where TOC is less than 1% there is inconsistency. The results obtained from the biomarker characteristics are in agreement with the results of Rock-Eval pyrolysis and indicated carbonate source rocks, which contain a mixture of marine organic matter with a minor amount of terrigenous organic matter. Biomarker characteristics also suggest that the organic matter was deposited in a marine environment under reducing conditions, and that Early Cretaceous source zones are at the stage of early oil window to peak of oil generation.
Tirgan formation of the Kopet-Dagh Basin (northeast Iran) represents one of the Urgonian carbonate platforms that were deposited during the Early Cretaceous time in the northern Alpine Tethys and ...deformed during the Alpine orogeny. In this study, six stratigraphic sections of the shallow-water platform sediments (Tirgan formation) were measured based on microfacies and fauna abundance. Detail study of petrography, fossil content, and sedimentary structures led to the identification of fifteen microfacies belonging to four facies belts including open marine, shoal, protected lagoon, and tidal flat. The sediments of the Tirgan formation exhibit calcareous green algae, abundant ooids, oysters, bryozoans, and crinoids in inner and middle platform ramp facies and planktonic bivalves and sponge spicules in outer-platform facies. Furthermore, the absence of basinal deposits and lack of evaporate evidence point to deposition under warm-temperate and humid climate conditions. Sequence stratigraphy analysis of Tirgan formation led to distinguish a single depositional sequence in all of the sections which are composed of transgressive and highstand systems tracts with sequence boundaries of type II (SB2). The lowermost lower Aptian Tirgan sequence in the study area relatively shows a similar trend in comparison with the global curve. This basin was deepened over time so that shaly and marly sediments of Sarcheshmeh formation were placed over Tirgan conformably and may suggest a drowning event that was likely related to unusual global warming. Last, this study contributes to the better understanding of the high distribution of facies assemblages in the Urgonian carbonate platforms.
To progress in the knowledge of Upper Triassic evolution of the central Tethys realm, an integrated approach which includes new sedimentological and sequence stratigraphy has described in central ...Iran. The Nayband Formation of Late Triassic age in central Iran is composed of various rocks of siliciclastic and mixed carbonate–siliciclastic deposits and represents an example of storm-dominated shelf deposition. Based on texture and sedimentary structures of the siliciclastic deposits, 11 lithofacies were identified and classified into three categories, i.e., conglomerate (Gms, Gcm), sandstone (Sp, Se, Sm, Sr, Hcs, Scs, Sh) and mud rock (Fm, F). These mainly consist of alternations of sandstone and shale, and constitute the lower and upper units of the studied section. The mixed carbonate–siliciclastic sediments crop out in the middle unit of the section. Based on field observations and petrographic studies, 12 microfacies were recognized which can be grouped into three depositional environments: shoreface (lower, upper), offshore-transition (proximal, distal) and offshore (upper, lower) on a storm-dominated shelf. Seven 3rd-order depositional sequences have been identified in this section based on field observations, facies analysis and sequence stratigraphy studies. The lower and upper boundaries of this succession are type 1 sequence boundaries (SB1); whereas, other boundaries are type 2 sequence boundaries (SB2). Depositional sequences are composed only of TST, MFS and HST, whereby the transgressive sequences (TST) mainly consist of deeper facies, and regressive sequences (HST) consist of shallower facies. Shelf transport was driven by the available accommodation space on the shelf and therefore was a function of eustatic sea-level fluctuations, but local tectonic activity has also controlled the thickness of the deposits.
Introduction This research study is based on knowledge-driven approach to synthesize the different parameters which rule on the formation of carbonate hosted zinc and lead deposits. The analysis of ...available data sets of the north Irankuh district demonstrates the complexity of decision making due to the different anomalous prospects introduced by geophysical, geochemical and surface evidences. Five known deposit/active mines, namely Gushfil, Zone 1 Gushfil, Blind, Tapeh Sorkh and Zone 5 Romarmar with total geological resources quoted as 13.4 million tons at 5.53% combined lead and zinc (Fig. 10) were selected to be examined in order to asset a knowledge-driven approach to the exploration of carbonate hosted zinc and lead deposits. The diversity of geometry, mineralogy and host rock of the deposits is tightly confined by the parameters surrounding the genesis of MVT deposits such as genetics of solutions, temperature of deposit formation, tectonic channel ways, different episodes of deposition of sphalerite and galena, hydrologic system of area, solution direction, wall rock reactions (Leach et al., 2010), depth of solution penetration, solution response to the Magnesian regime and metal bearing. Materials, Methods, and Procedures The present study consists of detailed underground and surface mapping, reinterpretation of district geology, detailed logging of about 100000 meters’ diamond drilling, ore geology, tectonic settings, deposits geometry, geochemical and geophysical survey within 7 square kilometers of north Irankuh district between the Gushfil and Tapeh Sorkh deposits. Discussion and Results Five known deposits in the north Irankuh district occur in the area of an intense detachment faulting (Fig. 1 and Fig. 5). The Gushfil, Zone 1 Gushfil and Blind deposits occur in north Irankuh reverse fault and Tapeh Sorkh and Zone 5 Romarmar in the trust fault. The deposits are confined to a certain stratigraphic unit locally called K3D (Figs. 2 and 3). Widespread regional selective dolomitization shows an extensive lateral movement from NW to SE and the depth of dolomitization in certain units drastically decreases. Two main regimes of solutions initially started with sphalerite and they were subsequently followed by galena the later of which is found in the secondary porosity. Mineralogy of the deposits is simple but the pyrite amount of the deposits varies from 2% to 20% which reflects the higher temperature of the solutions responsible for sulphide precipitation (Marie et al., 2001), geometry of the deposits and their distance to the current topography effect on chargeability values (Fig. 20). Sparry dolomite is found in three types as barren, with pyrite and light color sphalerite that occur in country rocks of all deposits except for the blind deposits. They can be used as a guide, addressing potential deposits. EPMA analysis revealed a considerable amount of Cadmium, Silver, Antimony, Arsenic and Copper within Sphalerite and Galena minerals (Fig. 12). Because of the semiarid climate in the area the decomposition of sphalerite, galena (Hitzman et al., 2003) and carbonate host rock has caused widespread distribution of Zn, Pb, Ag, Cd, Sb, As, Cu, Mn, Mg, Fe and Ca in the secondary halo of the area. The soil samples have been studied based on the static and machine learning methods (Figs. 13–A and B) by different researchers (Zekri et al., 2019). The anomalous areas based on geochemical studies have been tested by core drilling and the results are considered to be negative even in the area called Zone 3 which coincides with both geochemical and geophysical anomallies. In a different approach to understand the structure of geochemical elements the distribution of Zn, Pb, Ag, Cd, Sb, As, Cu, Mn, Ba together with elements such as Mg, Fe and Ca has been compared (Figs. 14, 15 and 16). The soils are heavily polluted due to widespread mineralization and no background value (Reimann and De Caritat, 2012) can be recognized. The comparative analysis of element concentrations in 5 selected populations in the studied area (Fig. 15) did not show any signs that could help recognize important anomalies from the false anomaly. However, it seems that the sudden decrease of Mg content (Fig. 17–C) in the area of Zone 3 (Zekri et al., 2019) is meaningful. Two geochemical profiles of soil samples crossing along this population and the next one crossing an active mine (Zone 5 Romarmar) (Fig. 18) provide us with a better understanding of the important anomalies versus the false anomaly since in the false anomaly the increase of Zn, Pb, Ag, Cd, Sb, As, Cu coincides with a sudden drop of concentration of Mg, Fe and Ca (Figs. 18–A and B). Recognition of ore containing strata (Sangster, 1995) is very important (Figs. 2 and 3) in locating successful drill holes in the exploration of carbonate hosted zinc and lead deposits. Eventually the use of data driven methods even opting advanced machine learning methods is not properly sufficient to recognize productive areas and we recommended the knowledge -driven approach.
Lower Cretaceous Shurijeh–Shatlyk Formations host some of the main reservoirs in the Kopeh Dagh-Amu Darya Basin. Exploration in this area so far has focused on the development of structural traps, ...but recognition of stratigraphic traps in this area is of increasing importance. Integration of 3D seismic data with borehole data from thirteen wells and five outcrop sections was used to identify potential reservoir intervals and survey the hydrocarbon trap types in the East Kopeh Dagh Foldbelt (NE Iran). Analyses of horizontal slices indicated that the lower Shurijeh was deposited in a braided fluvial system. Generally, three types of channel were identified in the lower Shurijeh Formation: type 1, which is low-sinuosity channels interpreted to be filled with non-reservoir fine-grained facies; type 2, which is a moderately sinuous sand-filled channel with good prospectively; and type 3, which is narrow, high sinuosity channel filled with fine-grained sediments. Results indicate that upper Shurijeh–Shatlyk Formations were deposited in fluvial to delta and shallow marine environments. The identified delta forms the second reservoir zone in the Khangiran Field. Study of the stratigraphic aspects of the Shurijeh succession indicates that both lower and upper Shurijeh reservoirs are stratigraphic reservoir traps that improved during folding.
Bangestan reservoir includes Sarvak and Ilam formations in the Mansouri oilfield consists mainly of carbonate rocks. In this research, we tried to overcome the problems in reservoir studies using ...well-logs data which are available in almost all wells in the oilfield. For this purpose, well-logs data from wells A and C were used as input data for the construction of electro-facies modeling. In the following, a model with 5 electro-facies was created and then this model was calibrated by microfacies in well A and core data such as porosity and permeability in the both wells in related to Sarvak Formation (wells A and C). The results of calibration reveal a good correlation between core data and electro-facies, so this model was propagated to un-cored wells in oilfield. The results of the study showed that reservoir quality from electro-facies 1 to 5 increases, respectively and pay zones of 2 in Ilam, 4 and 6 in Sarvak formations have the best reservoir quality. In order to future study, the velocity deviation log (VDL) that is mainly dependent on the type of dominant porosity in reservoir, was investigated to the specified electro-facies. Therefore, this log can be used as a tool for establishment of connection between porosity types and petrophysical data such as electro-facies.
The present study investigated the geochemical characteristics of Shemshak shales as a probable oil source rock in the Gushfil mine located in the Sanandaj-Sirjan Zone (SSZ), Iran. Trace elements ...such as nickel, vanadium, chrome, molybdenum, and cobalt are used as paleoenvironmental indicators. Moreover, the ratio of these elements shows that oxic to disoxic conditions prevailed during the sedimentation period. The interrelation of these elements indicates that the upper part of Shemshak Formation of the Jurassic age was deposited in a terrestrial to the marine-terrestrial influenced environment. The solid bitumen reflectance (BR) documents that the black shales presently are overmature. Conjugation of BR and the insolubility of organic matter in carbon disulfide illustrates the presence of pyrobitumen and its subgroup epi- to meso-impsonite, which is also characterized by the absence of any fluorescence under ultraviolet light. The ratio of light to heavy hydrocarbons proves that the type of solid bitumen before pyro-bituminization has been a primary-oil solid bitumen, which could migrate through fractures and coarse pores. The primary-oil solid bitumen might be derived from Kerogen types II and III as documented by fibrous plant fragments, translucent phytoclasts and pollens. Presently, due to intense degradation, kerogen type IV dominates. The modeling confirms that a thermal degradation had probably occurred after the deposition of Lower Cretaceous carbonates when the shales were able to produce bitumen. Ultimately, intense hydrothermal degradation led the solid bitumen to evolve into pyrobitumen and caused the shales to evolve into a dry gas window.
Geochemical analysis of sandstones from the Sardar Formation (from two stratigraphic successions) in east‐central Iran were used for identification of geochemical characterization of sandstones, ...provenance and tectonic setting. Sandstones in the two lithostratigraphic successions have similar chemical compositions suggesting a common provenance. Bulk‐rock geochemistry analysis of Carboniferous sandstones from Sardar Formation indicates that they are mainly quartz dominated and are classified as quartzarenites, sublitharenites and subarkoses, derived from acid igneous to intermediate igneous rocks. Discrimination function analysis indicates that the sandstones of Sardar Formation were derived from quartzose sedimentary provenance in a recycled orogenic setting. Also, major and trace elements in sandstones of Sardar Formation (e.g., K2O/Na2O vs. SiO2) indicate deposition in a stable passive continental margin (PM). Chemical index of alteration (CIA) for these rocks (> 65%) suggests a moderate to relatively high degree of weathering in the source area.
Evaporite deposits are increasingly recognized for their role in developing oil reservoirs. In the Shadegan Oilfield, anhydrite is an evaporite mineral identified in the Asmari Formation ...(Oligocene-Miocene) as clastic- and carbonate-evaporite assemblages. Our study found that diagenesis plays a critical role in controlling the distribution of different fabrics (texture and structure) in the area. The anhydrites resulted from two progressive processes: early diagenesis and formation of anhydrites related to supratidal to shallow settings, and late diagenesis and crystallization of anhydrites in deeper environments. The evaporite-bearing intervals provide an opportunity to investigate the interactions between sea-level fluctuations and the growth of anhydrites during the development of the carbonate ramp of the Asmari Formation. Despite previous studies on the Asmari Formation, little is known about the relationships between the occurrence of its anhydrite fabrics and sequence stratigraphic framework. In our study, the continuous shallowing-upward trends, exposure of sediments, and subsequent diagenesis were responsible for the deposition of anhydrite. Semi-arid to arid climates followed, resulting in stacking of anhydrite and dolomites, particularly in the upper parts of the Asmari, corresponding to the Burdigalian.
•Types of anhydrite fabrics in the Asmari Formation were developed during early and late diagenetic stages.•There is a direct relation between increasing dolomitic intervals and the occurrence of anhydrite.•Anhydrite fabrics show high abundance and diversity within the highstand system tracts of depositional sequences.•Arid climatic conditions in Burdigalian led to the increase of anhydrite at the top of the Asmari Formation.
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