نشریه رسوب شناسی کاربردی
پیاپی 18 (پاییز و زمستان 1400)

Asmari carbonate formation in Qale Nar oil field is one of the most important oil reservoirs in Dezful embayment. This reservoir has a lot of heterogeneity due to intensive changes in the sedimentary environment and diagenetic processes, which makes it very difficult to predict the petrophysical properties of the rock in reservoir. Creating a logical connection between sedimentary and electrical facieses, it can be effective in better understanding the reservoir and reducing uncertainties. In this study, using petrographic data and core description in six wells, 7 limy facies associations and one coarse crystalline dolomite were identified. Based on the petrophysical well logs of gamma, neutron, density, acoustic and photoelectric, and using Geolog software by MRGC algorithm, 5 electrofacieses (from 1 to 5) of the reservoir were determined. Electrofacies 1 has the best and electrofacies 5 has the worst reservoir quality. Examination of the frequency of electrofacies shows that good and very good electrofacieses make 30% of the Asmari reservoir of Qale Nar oilfield.

In the present study, the limestone unit of the Pabdeh Formation was investigated in Bankul  stratigraphic section in the northeast of Ilam and compared with other outcrops of this unit. The studied unit is 73m in thickness and formed by thin to medium -bedded limestone. According to the identified index microfossils, four biozones were recorded: 1) Assemblage Zone 1, which is equivalent to the upper part of Acarinina topilensis Partial Range Zone; 2) Morozovelloides lehneri Partial Range Zone; 3) Orbulinoides beckmanni Taxon Range Zone. As a result of this study and based on the identified planktonic foraminifera, the age of the middle part limestone of the Pabdeh Formation is Lutetian –Bartonian and correlated to the Shahbazan Formation. The sedimentation of this unit has been contemporary with global temperature decrease and eustatic sea level decrease. Meanwhile, the limestone unit at the base of the Pabdeh Formation in the Early Eocene age in the south of Lorestan has a shallow facies and is equivalent to global warming and rising eustatic water level. This was the same condition in Izeh zone. In the north of Dezful, there was the opposite of these conditions, so that in the Middle Eocene, the limestone unit of Pabdeh Formation had a shallow facies. This difference in facies has probably been influenced by various tectonic movements in the Lorestan foreland zone.

The present study aims to evaluate the effect of monsoon seasonal variations on sedimentology and beach profile of the Chabahar Bay. Based on the above data, during the monsoon, Chabahar Bay sedimentary environment is categorized into Tis and desalination plant coasts (sand), Konarak (clay), and mouth of the Chabahar Bay (clayey sand). On the other hand, after monsoon the area is divided into Tis (high sand content), Konarak and mouth of the Bay (high silt content), and desalination plant (the same contents of sand and silt). Data revealed that the high-energy SSE monsoon waves carry small particles to offshore leading to increase the proportion of sand particles in the eastern and central parts of the bay (onshore and offshore Tis and desalination plant coast). However, as is sheltered by a headland, the western part of the bay (onshore and offshore Konarak) is lesser affected by monsoon waves and therefore is covered by finer sediment particles (mostly clay). Longshore currents are likely responsible for fine-grain sedimentation in Konarak as well. After the monsoon, however, wave energy weakening leads to deposition of finer grain sediments and formation of sand bars and berms along coasts Chabahar Bay. This sedimentation/erosion regime causes lack of considerable sedimentation around harbours located in the eastern part of the bay (Shahid Kalantari, Shahid Beheshti, Hafte Tir and Tis), while the Konarak harbor (west of the bay) is faced by a severe sedimentation.

Cenomanian –Turonian carbonate sequences of the upper Sarvak Formation are among the most important hydrocarbon reservoirs of the Zagros area in SW Iran. Depositional and diagenesis histories were investigated using the petrographic studies of core samples and thin sections of this formation in 6 wells from 5 oilfields located in central and southern parts of the Dezful Embayment. Facies analysis has resulted in the recognition of 14 microfacies that are grouped into six facies associations (basin, outer ramp, middle ramp, open marine lagoon, shoal, and restricted lagoon), according to their facies characteristics and comparison to the standard microfacies models. A homoclinal ramp model was proposed as depositional setting of the Sarvak Formation. Important diagenetic alterations of this formation include dissolution, cementation, dolomitization, de-dolomitization, silicification, neomorphism, compaction, and fracturing. They represent a paragenetic sequence of marine, meteoric (eogenetic and telognetic), and shallow- to deep burial realms. Sequence stratigraphic interpretations resulted in the differentiation of two (third-order?) depositional sequences in the upper Sarvak Formation (mid Cenomanian – early Turonian). Finally, facies characteristics and diagenetic alterations are interpreted in a sequence stratigraphic framework.

Qalikouh anticline is located 35 km southwest of Aligudarz city, Lorestan province, SW of Iran. The area is located in the high structural zone of Zagros. The oil shales of the areas are located in the Middle Jurassic and Lower Triassic of Sargelu and Garu Formations. The Sargelu Formation contains a series of shale, carbonate, oil shale, and clays. Garau Formation includes oil shale horizons with different thicknesses, ammonite shales, and black cherty layer. The shales of these two formations in the high Zagros region have formed oil shale reserves due to their richness in organic matter (OM), kerogen type is I and II, and relatively low thermal maturity at the beginning of the oil window. This study focuses on the effect of geochemical processes on the enrichment of trace elements and their interaction with organic matter in Qalikouh oil shale. analysis was performed by XRF, XRD, ICP-Ms, and Rock-Eval methods and Statistical significance were analyzed. The results of this study indicated the high enrichment of elements Cd, Mo, Ag, U, Cs. The correlation between immobilized and mobile oxides, organic matter, formed minerals, and other factors were tested. These tests revealed that the enrichment of trace elements is affected by classical, biological, and autogenic materials. Elements U, V, Cd are related to the organic and autogenic matter. Elements Ca, Si, P is of biological origin, and elements Ag, Ti are of classical origin.

Carbonate and siliciclastic Aghchagil and Apsheron Formations has been studied in a subsurface section in the Gorgan Plain. The Aghchagil Fm. consists of lower sandstone and upper carbonate units in the studied area. Sandstones petrofacies include litharenite, sublitharenite and feldspatic litharenite. The grain-supported facies is dominated in this Fm. and displays abundant porosity as moldic, vuggy and fenestral forms specially in the carbonate sediments, which indicates considerable lithological differences in Iran and the neighboring countries like Azerbaijan and Turkmenistan. These features candidate the Aghchagil sediments as prone reservoir succession, hence emphasizes a comprehensive geological and exploration study in the studied area. The Apsheron sediments can be sub-divided into lower sandstone and upper mudstone units and consist of sandstone with litharenite and sublitharenite petrofacies and ooidal/bioclastic limestone and gray/brown mudstone/claystone. Based on the youngest nannofossil species the late Pliocene-lower Pleistocene and middle Pleistocene ages are defined for the in the Aghchagil and Apsheron Fm., respectively. Nannofossils distribution of the studied succession displays the SCB was connected to the Black Sea and Mediterranean Basin in the lower Pleistocene and middle Pleistocene and was isolated in the late Pliocene-earliest Pleistocene.

Sequence stratigraphy of the Qom Formation deposits (in two stratigraphic sections) in the Natanz-Qom region has been studied. The Qom Formation outcrops in the Natanz section (with Rupelian?-Chattian-Aquitanian age and 330 m thickness), consist mainly of medium to thick-bedded and massive limestones, reefal limestones, shale, and marl. They are underlain by the Eocene volcanic rocks and unconformably overlain by the quaternary alluvium. The Qom Formation deposits in southeastern Qom (Khurabad section; with Rupelian-Burdigalian age and 260-m thickness), consist mainly of medium to thick-bedded and massive limestones, marly limestones, marl, evaporate deposits and siliciclastic deposits. They are underlain by the Eocene volcanic rocks and disconformably overlain by the Upper Red Formation (URF). Fourteen different microfacies, belonging to open marine (middle ramp), lagoon (inner ramp) and peritidal zone were recognized. Based on the field investigations, deepening and shallowing patterns in microfacies, staking patterns and the distribution of foraminifers, three third-order sequences in the Natanz section and five third-order sequences in the Khurabad section have been identified. These depositional sequences are bounded by both type 1 and type 2 sequence boundaries. Sequence boundaries are mainly characterized by the abrupt change in lithology and biotic components. In the Natanz section, only the transgressive systems tracts (TST) and the highstand systems tracts (HST) were recognized; while in the Khurabad section, the lowstand systems tracts (LST) were also recognized (in two third-order sequences). The transgressive systems tracts (TST) of sequences show deepening-upward facies trend, whereas the highstand systems tracts (HST) have a shallowing-upward facies trend.

Rivers, as the living artery of the watershed, have played a decisive establishment of civilizations. But today, large amounts of pollutants enter the aquatic ecosystems, due to overpopulation and the expansion of industrial and agricultural activities. Among these, heavy elements are of special importance due to their stability, non-degradability, toxicity and bioaccumulation potential. Therefore, in this study, potential toxic elements ( AS, Cd, Cr, Ni, Cu, Pb, Zn) were investigated in order to determine the concentration, contamination factor and degree of contamination, geo-accumulation index, Enrichment and to detect the level of pollution caused by them. For this purpose, 21 surface sediment samples were collected based on the distribution of point and non-point pollution sources and river morphology. Samples were conditioned and concentration of toxic elements and sulfur were measured using ICP-MS at dry weight with accuracy of mg/kg and percentage of total organic carbon. Using enrichment factor and sediment quality standards (ISQGs, PEL, SEL), the level of contamination caused by toxic elements was detected. Hierarchical clustering analysis (AHC) with pearson similarity coefficient was used to identify metal elements with similar behavior in river sedimentary environments and the most important cationic adsorbent such as organic matter and clay particles using XLSTAT2018 software

This study shows that chaetetids display morphologies similar to such benthic organism as stromatoporoids, bryozoans and corals .Most of the chaetetids in the Esfandiar are tabular and bulbous forms. Chaetetid sponges occur mainly as hemispheroids up to a diameter of 60 cm, being more common towards the platform margin. Chaetetids clearly grew in shallow-water marine environments and they are usually inferred to indicate a shallow subtidal environment. Fossil chaetetids were a conspicuous component of reefal and associated environments during the late Paleozoic (late Carboniferous and Permian) and part of the Mesozoic (Middle Triassic into the Cretaceous) in the Tethys but were mainly dispersed in the Esfandiar platform. Hypercalcified sponges with a chaetetid skeleton are members of the marine sessile benthos. The skeleton of hypercalcified demosponges is a rigid a specular skeleton, or a combination of both .Growth forms of chaetetids in the Esfandiar Formation are: bulbous, domical, laminar and complex. At the base of the Esfandiar Formation, most of the chaetetids have ragged margins indicating episodic sedimentation and others that were reoriented during life show changes in growth directions.Bioclastic rudstones and bioconglomeratic layers indicate in situ reworking by storms of the platform sediments. The predominance of large chaetetids may reflect particularly strong storm events or proximity to the platform margin. At the high-energy platform margin, ooid shoals protected the platform interior from the open sea during the Middle Oxfordian to Lower Kimmeridgian,

Asmari-Jahrom reservoirs are one of the main fractured reservoirs in the southwest of Iran and the world (Nelson, 2001). It is very important to study the role of these fractures in increasing the permeability and movement of hydrocarbons along these reservoirs (Alavi, 2004, 2007; McQuillan, 1986). In this study, petrophysical logs (NPHI, RHOB, DT, GR) and image logs (FMI) in GEOLOG 7.0 and CIFLOG software were investigated. Finally, by calculating the amount of fracture and vuggy porosity and correlating them with velocity deviation log (VDL) and fracture parameters (VAH, VDC), it was shown that the amount of fracture porosity is directly related to fracture aperture (VAH) and where the velocity deviation log is negative and low, fracture parameters especially the VAH diagrams show the high peaks. Also, the predominant type of porosity in the reservoir based on the velocity deviation log is the matrix (primary) porosity, which at some distances, fracture porosity and vuggy can be seen in the reservoir. Finally, based on indirect evidence (drilling mud wastage), type of the porosity (matrix, fracture and vuggy), the amount of porosity and the quality of oil saturation in the well, 18 zones were identified, which to determine the quality zone (s) with appropriate reservoir quality. In Asmari Formation of the studied well, in the depth range of 2225 to 2250, the highest fracture density is observed, based on which Zone No. 4 can be introduced as the region with the highest relative permeability for this formation. Also, the highest fracture density in Jahrom Formation is between 2475 to 2569 depth range, which can be said that Zone No. 16 has provided the highest permeability in the Jahrom Formation.

Yadavaran oil field is one of the oil fields in Iran which located 130 km west of Ahwaz, at a zero point border with Iraq and in the vicinity of the Hural Hoveyzah wetland, and is located in the Iraqi Majnoon field in a joint oil reservoir. The most important reservoir of this field is the Sarvak Formation (Upper Albian- Turonian) from the Bangestan Group which, together with the Ilam Formation, forms the second major reservoir of Zagros Basin after the Asmari Formation. In order to evaluate the reservoir characteristics of the Sarvak Formation based on petrophysical and petrographical data in Yadavaran oilfield, one well was selected and analyzed. Based on the petrophysical cross plots, Sarvak Formation with the thickness of 640 meters is conformed of limestone. Based on the study of 500 thin sections of the cutting samples and cores, 10 carbonate microfacies were identified that were deposited in a carbonate ramp. Major diagenetic processes affecting the Sarvak Formation include neomorphism, bioturbation, micritization, dissolution, cementation, compaction, piritization, hematitization, and fractures. The main types of porosities identified in Sarvak Formation are vuggy porosity, intercrystaline, molding, and microscopic fractures, which have higher permeabilities than the other porosities detected. The sum of petrographic and petrophysical studies showed that the Sarvak reservoir can be divided into 5 main reservoir zones and 4 sub-reservoir zones (9 in total) in the study area. Zone number 2, sub-zone 4-1, 4-3, and some parts of sub-zone 5-2 have good reservoir quality. Studies also showed that ...

In order to conduct stratigraphic and paleoenvironmental studies in the Gurpi Formation, the sediments of this formation in a borehole in the Marun Oilfield located in southwestern Iran based on calcareous nannofossils were studied. In this study, Gurpi Formation consists of 10 rock units consisting of marl, marly limestone, limestone and shaly limestone. Also, the study of biostratigraphy based on calcareous nannofossils led to the identification of 22 genera and 43 species. Based on distribution of the index species have been recognized biozones, including Calculites obscurus Zone (CC17/ UC13), Aspidolithus parcus Zone (CC18/ UC14), Calculites ovalis Zone (CC19/ UC15aTP),Ceratolithoides aculeus (CC20/ UC15bTP), Quadrum sissinghii (CC21/ UC15cTP), Quadrum trifidum (CC22/ UC15dTP - UC15eTP), Tranolithus phacelosus (CC23/ ‌UC16-UC17), Reinhardtites levis (CC24/ UC18), Arkhangelsiella cymbiformis (CC25/ UC19- UC20aTP- UC20bTP), Nephrolithus frequens (CC26/ UC20c, dTP)‌, that corresponding to UC13- UC20dTP. According to the identified bio-zones, the age of the Gurpi Formation in this section is late Santonian/early Campanian to latest Maastrichtian. The paleoenvironmental study indicates that the basin depth has increased for the deposition of the Gurpi Formation in the Late Santonian. Following this, the deposition of the Gurpi Formation continued until the Late Maastrichtian, so that the last bio-event related to the Gurpi Formation is the first occurrence of Micula prinsii in this formation. Then, at the end of the Last Maastrichtian, with the drop of sea level, the deposition of this formation in this oil field was completed, which followed by the Pabdeh Formation with a sedimentary gap on the Gurpi Formation.