نشریه زمین شناسی کاربردی پیشرفته
سال دوازدهم شماره 43 (بهار 1401)

Nowadays, according to the increase in fuel demand, the oil wells drilling process has increased to exploit the reservoirs. The most important issue in oil and gas wells drilling topic, is the appropriate drilling rate and reducing the cost. Studies and the usage of geomechanical methods can play an important role in this matter. One of the studies regarded to the topic of reducing drilling costs that has received a lot of attention today is the well wall stability and determining the appropriate mud weight to avoid instability in the well wall. In recent years, a lot of research has been done in this field. In the present study, the well wall stability status of one of the excavated wells in Iran’s southwest oil fields, in 88.3 inches, in the upper section of Sarvak Formation was analyzed by using analytical and numerical methods through FLAC3D software. The input parameters in this research are obtained by interpreting the data from Dipole Shear Sonic Imager (DSI), the logs from Formation Micro Imager (FMI), density, caliper and gamma, MDT tools and also from the daily excavation and geology reports. Also, the window for the required mud weight to meet the dissipation situations, fracture opening, well wall symmetric downfalls, and well eruption was determined. The beneficial results of this study can be used to reduce the time spent on excavating the wells in the investigated field in the future, which results in saving drilling costs.

The Alvand batholith contact aureole hornfelses in south of the Serkan area (NW Hamedan province) contain metamorphic assemblage cordierite + garnet + biotite + plagioclase + K-feldspar. Whole rock compositions of the hornfelses show that they formed by metamorphism of a pelitic protolith (with some CaCO3 impurities) that originated from weathering of felsic to intermediate igneous rocks. Electron microprobe analyses indicate that the cordierites and biotites are of Fe-rich associations, the garnets are rich in almandine and spessartine and the plagioclases are oligoclase. Thermobarometry calculations using the in-equilibrium minerals obtained 550 to 620 oC T and >3 kbar P for these rocks. Also, the calculated pseudosections for average composition of these rocks demonstrate that the cordierite + garnet assemblages occurred due to high Mn and Ca contents of the garnets, high Mg contents of the cordierite and probably during uplifts during intrusion of the igneous bodies. Moreover, investigation of variations in fluids during metamorphism show that stability of the cordierite + garnet assemblages needed some CO2 contribution.

Chalderan shear zone (SCZ) is located 270 km north of Urmia and 868 km west of Tehran. The structural and microstructural studies show two groups of the main structure in this area. The first group includes structures related to inclined shear movements, which include: asymmetric mantled porphyroclasts, fabric C and S and mineral fish structures, and the second group is related to thrust movements that occur in this area. The inclined shear movements are created by inclined transpressional strike slip component and thrust movements are created by inclined transpressional component. There is kinematic evidence of the function of shear and transpressional stresses in this region, all of which indicate the function of a shear zone with a moderate slope mylonitic foliation to the northeast and stretching lineation to the northeast with inclined strike slip mechanism with inverted component in this region. In the study area, we proposed inclined dextral transpression strike slip model.The fact that the structures and microstructures indicating reverse shear and inclined strike slip in this zone are observed with each other indicates the occurrence of partitioning in this shear zone. This indicates that tectonic forces inclined to Chalderan shear zone deformation zone occurred due to transpressional tectonics between Arabian plate and Central Iran block in northwestern Iran.

Varzeqan plain is exposed to extensive agricultural and mining activities, as well as the presence of nitrate and arsenic anomalies in the water resources and supplying drinking water from groundwater resources need to asess the groundwater quality. The results of the analysis of groundwater resources in Varzeqan plain in 39 sampling points for 13 effective parameters including major, minor and trace elements, physical and chemical properties, were used to determine drinking water quality. Results of health risk for groundwater consumers and according to the standards of the World Health Organization (WHO) and the Iranian Industrial Research Standard (ISIRI), show that the most effective of these parameters in the quality of drinking water is nitrate and arsenic. In this study, GQI and GWQI indicators were used for evaluation, and according to the output maps of these two indicators, which show the difference in determining the quality of drinking water in the region, It was not possible to select one of these two indicators to determine the drinking ability of water resources in the region, In order to achieve a single map that more accurately expresses the quality categories of drinking water in the area, the unsupervised method was introduced and used, and the results show that the unsupervised method with a higher CI than the results of the two indicators is a more ideal method for assessing the quality of water resources in the region and it is more accurate to determine the drinkability categories of these resources.

Morphogroup analysis, due to independence of species level taxonomy, as wel as permit to comparison of assemblages of differing ages, is a useful tool for ecological and palaeoecological interpretation. Foramniferal study of the Qom Formation in the Natanz (with Rupelin-Chattian?-Aquitanian in age and 330 m thickness) and Khorabad (southeastern Qom; with Rupelin-Burdigalian in age and 260 m thickness) sections resulted in identification of 8 morphogroups. The morphogroups were distinguished according to test/shell morphology and architecture (general shape, mode of coiling, and arrangement and number of chambers), inferred life habitat either living on the surface of the sediments or within the sediments (epifaunal and infaunal), and feeding strategy. Generaly, epifaunal morphogroups were dominated in both study sections. The lower 200 m of the Natanz section, are dominated by calcareous porcelaneous morphogroups; while the upper layers are dominated by hyaline morphogroups, which indicates the lower and upper parts were deposited in inner ramp (lagoonal environments) and open sea, respectively. This significant change through time reffers to gradual increasing of the basin depth, decreasing the light intensity, reducing the salinity and decreacing the nutrient level. The distribution of morphogroups in the Khorabad section follows a reverse pattern; so that, despite the minor fluctuations, the lower 200 m of the Khorabad section, are dominated by hyaline morphogroups; while the upper layers are dominated by porcelaneous morphogroups, which indicates the lower and upper parts were deposited in open sea and inner ramp (lagoonal environments), respectively.

Khosrow Abad iron skarn deposit is located in the northwest of the Sanandaj-Sirjan structural zone, in the western segment of the iron metallogenic zone (Sonqor series). Its geological units include skarnified meta basaltic andesite, crystallized limestone and quartz monzonite intrusion. The main minerals in the prograde and retrograde skarn zones are; garnet, clinopyroxene, epidote, albite, actinolite, chlorite, dolomite, calcite, quartz, serpentine, and talc. Geothermometry of skarn development was evaluated using skarn silicate minerals pair, verified by the microthermometry and calcite twining deformation. The estimated temperature from the two-feldspar geothermometry in the quartzmonzonitic intrusive body (endoskarn) is in range of 507º to 805ºC. The geothermometry of garnet-clinopyroxene pair minerals, indicate temperatures of 301º to 567ºC for prograde skarn zone. Based on chlorite and calcic amphibole geothermometry, the calculated temperatures are in range of 129º to 315ºC and 216º to 332ºC respectively. Geothermometry of the retrograde skarn zone is consistent with the microthermometry of fluid inclusions in calcite and deformation of calcite twining in crystallized limestone (170º to 300ºC) and skarn (127° to 142°C) unit. Andradite is stable at temperatures above 430 °C, even under high sulfidation conditions. At temperatures below 430 °C and relatively high fugacity of sulfur (more than 10-6), andradite altered to the complex of calcite, quartz and pyrite. With decreasing of fS2 (about 10-6), such fluids form magnetite complex. Therefore, it can be concluded that retrograde metasomatizing fluids in Khosrow Abad iron skarn deposit had a sulfur fugacity of 10-6.5 and a temperature of more than 430 °C.

In this research, the role of lithology and mineralization in the abundance of naturally occurring heavy metals in sand sediments of the rivers flowing surrounding the Dashkasan gold mine located in the northeast of the Qorveh city was evaluated. For this purpose, 30 samples were taken from 20 cm deep underground surface. The concentration of Fe, Ba, Zn, Cr, Pb, Cu, Co, As, Sb and Cd was measured in the medium sand size sediments and surface/groundwater samples. Thin/polish sections were prepared from the heavy mineral content of the sediments. According to results of the study, the amount of opaque heavy minerals is positively correlated with the concentration of Ba, Pb, Zn, As, Sb, Fe and Cd. Feldspar shows significant positive correlation with As and Ba. The volcanic rock fragments are correlated with Pb, Zn, Sb, Ba, As and Fe. There is positive correlation between the metamorphic rock fragment content of the sediments and Cr concenttration. Hornblende and biotite show relatively low positive correlation with Co, Cd and Ba. Sb, As, Pb and Ba have extremely high enrichment in the sediments, Cd is slightly enriched and other elements are depleted. According to the Point Load Index (PLI), most samples are classified as polluted. Based on the Igeo index, As and Sb fall into highly to extremely polluted classes and Cu, Co, Cr, Zn, Fe, Pb, Cd and Ba place between the unpolluted to slightly polluted classes.

Dezful Embayment is the most important fertile oil province of the Zagros Fold-Thrust Belt. It includes several incompetent strata as basal and intermediate detachment levels that play a significant role on the structural styles and hydrocarbon preservation. The Oligocene–Miocene deposits of the Asmari Formation are the most important oil reservoir in the Zagros fold–thrust belt in southwest of Iran. The Aquitanian evaporites of Kalhur Member of the Asmari Formation were deposited in north Dezful Embayment. Based on the interpretation of seismic profiles, the influence of the evaporitic Kalhur Member of the Asmari Formation on the geometry of deformation was obvioused in different parts of the north Dezful Embayment. Determining the geometry variations in the different depths reduces the uncertainties of petroleum exploration. Parsi Field is a slightly asymmetric NW-SE trending anticline lying in Khuzestan, at the southwest edge of the Zagros mountain belt in the north central part of the Dezful Embayment. The Asmari reservoir in the Parsi field comprises various combinations of limestone, dolomite and anhydrite. These deposits form a major partin Oligo-Miocene carbonate ramp system. In this research, the effects of the Kalhur detachment horizons on the folding style of the Parsi oil field have been investigated using seismic and subsurface well data

Asmari Formation, comprises mixed carbonate-siliciclastic lithologies in the central Dezful Embayment, with thick shale intervals at the base. In this study mineralogy, organic petrography, thermal maturity and generation potential of the basal shale sediments of the Asmari Formation is investigated in Ahwaz, Marun and Kupal oilfields. Clay mineralogy including kaolinite and mixed layer illite-smectite are the most abundant minerals. Secondary important minerals are calcite and quartz. Microscopic examinations indicate that the organic matter in this unit have mostly originated from continental settings and comprises vitrinite, inertinite, pollen, woody phytoclasts with minor marine liptinite macerals and amorphous materials. TOC contents range from 0.2 to 1.25 wt.% (avg. 0.75 wt%), indicating poor to fair oil generation potential. HI values ranging between 141 to 244 (mg HC/g TOC), is consistent with type III and II/III kerogen. The dominance of terrestrial organic matter (kerogen type III), with relatively high oxygen index indicates that the organic matter was most likely deposited under oxic/suboxic conditions when the relative sea level was low. Vitrinite reflectance (0.45-0.7 %Ro) and Tmax values (417-444 ℃, avg. 432 ℃) suggest that the Asmari basal shale is thermally immature to early mature in the study area.

Hararan deposit is located 110 km northeast of Baft city, Kerman province. This area is located on the Urmia-Dokhtar belt. The predominant lithology in the area of ​​Hararan copper deposit includes a collection of volcanic and igneous rocks with shallow infiltration massifs. One of the important features of this region is the intense volcanic activity and the formation of the volume of potassic, argillic, proplitic and siliceous alterations due to the influence of igneous masses into volcanic rocks, which is related to the Eocene. In the host rock of Hararan deposit, more mineralization can be detected in the form of veins, veinlets, under the control of open spaces of fractures and stockwork. The area has alleles of algal, potash, propolitic and silicification alteration. Mineralization in siliceous alteration zones may be associated with amounts of gold and the elements silver, arsenic, and antimony. Supergene processes are observed in potash and propylitic zones with outcrops of malachite, neocyte minerals and in argillic zone with jarocyte and goethite minerals. The data obtained from the study of quartz mineral fluid intermediates show that mineralization is formed in the temperature range of 110 to 410 ° C. The highest salinity rate was between 4 and 21% by weight equivalent of NaCl. Field evidence and microscopy of fluid intermediates in the quartz mineral of the Hararan deposit show that the ore-forming fluid is very similar to epitermal.

A stratigraphic section was selected in East Garkan in order to study the paleontology of the Qom Formation ostracods in Urumieh -Dokhtar Zone. In this section, Qom Formation is gradually located on the clastic rocks of the Lower Red Formation and with disconformity under the Upper Red Formation. A total of 10 species of 14 ostracods genera were identified. The common stratigraphic range of these ostracods and the presence of accompanying foraminifera confirm the Late Oligocene (Chattin) age for the desired layers. The ostracod and foraminiferal assemblage from the studied section shows that the Qom Formation has accumulated in a warm and oxygen-rich environment. Based on the study of 60 samples found from the studied section, two sedimentary environments of the estuary (including alluvial channels, barrier; central basin and intertidal) and shelf (including inner, middle and outer shelf) were identified. The ostracods are spread in the middle of the side bay and the outer ramp.

Soil is one of the essential building materials, and the primary support of structures has long been a human interest. However, due to weakness in shear strength and lack of resistance to tensile forces, researchers have consistently sought to increase its bearing capacity, strength, and improve its properties and various methods including mechanical modification such as compaction, chemical modification such as treatment with lime, cement or salt. The purpose of this study is investigation of the effect of sodium chloride salt on the geotechnical properties of loess soil. Loess soil was sampled from a Golestan province region and transferred to the Soil Mechanics Laboratory of the Shams University of Gonbad-e-Kavos. Sodium chloride salt was added to soil sample with content of 3, 6 and 9% by weight of soil. Soil samples were prepared in normal condition (without additives) and with different content of sodium chloride for geotechnical properties tests. The results show that the addition of sodium chloride salt reduces the plastic and liquid limits in the Atterberg limits test, increases the dry weight unit weight and decreases the optimum moisture in the compaction test, increases the strength in the unconfined compressive strength test and increases the cohesive and friction angle in the direct shear test.