نشریه علوم زمین خوارزمی
سال ششم شماره 2 (پاییز و زمستان 1399)

One of the most important steps in the study of hydrocarbon reservoirs is the determination of rock types. Determining of reservoir rock type can be done either based on the grouping of lithological, petrophysical and geological characteristics of the reservoir rock or based on the dynamic properties and fluid permeability in rock units. The first method is mostly accepted by geologists and specialists in making fine-grid geological models, while reservoir engineers rely more on this based on fluid flow behavior. In other words, the classification of reservoir rock depends on various parameters such as rock fabric, type of cavities, porosity, permeability, size distribution of the pore throats and capillary pressure. In this paper, all core data including static and dynamic data as well as the results of interpretation of logging data have been used to determine rock types in one of the carbonate reservoirs in the Persian Gulf. In this study, the matching of water saturation data obtained from special core analysis and petrophysical interpretations has been used in order to more accurately determine rock types.

The utilize of Kaiser effect during acoustic emission testing is a novel approach for computing the amount of stress in the rock, which has been tremendously exploited due to the immense reduction in the cost and time of determining the in-situ stress. The Felicity ratio is a precise and appropriate criterion for assessing the accuracy in the evaluation of the Kaiser effect. Numerous factors influence the accuracy of the Kaiser effect. This paper investigates the effect of anisotropy on the Kaiser effect on the rock. For this purpose, acoustic emission effect in the unconfined compression test on the Phyllites specimens with various angles of anisotropy (0, 30, 60, and 90°) has been conducted. The results demonstrate that in all unconfined compression tests, the Felicity ratio of acoustic emission is close to one. In other words, the anisotropy does not have a significant effect on the values of the Felicity ratio. In addition, the results show that the unconfined compression tests are more accurate in determining the Kaiser effect.

The coal seams of the Hojedk Formation have appropriate thicknesses, but the exact age of their permeable beds in the Sarapardeh stratigraphic section is indeterminate. In this study, we use the main plant groupschr('39') fossils of these beds to precise age dating. This study led to identifying 18 species belonging to 13 genera and 7 orders of plant fossils. In Sarapardeh section, coal beds include d0, d2, d3, d4, d5, d8, d9, d12. Phlebopteris angustiloba is the most abundant and well-preserved species associated with the d2 coal seam, which is the main industrial coal bed and is very thick in this section. This species is introduced from Iran with the new Middle Jurassic age for the first time. According to the index species Klukia exilis, Eboracia lobifolia, Nilssonia friziensis, Bajoician-Bathonian age is suggested for coal layers d3, d5, and d8. The floral gradient score (59) in the Sarapardeh stratigraphic section is comparable to the Kalshaneh area of Tabas (58.5), which indicates a humid and subtropical climate.

Dacitic volcanics are broadly exposed in Azerbaijan area (south of Julfa). They show SiO2 contents of 66.4 to 69.9 wt.% and calk alkaline nature. The (La/Yb)N ratio ranging from 19.05 to 40.7 suggests highly fractionated rare earth elements (REE) and relative enrichment of light REE to heavy REE. The normalized multi-element diagrams are characterized by Rb, Ba and K enrichment as well as Nb, Ta and Ti depletion reminiscent of subduction- induced magmatic processes. Based on major element contents such as SiO2, Al2O3, MgO, Na2O, K2O, K2O/Na2O, Mg# and trace element values of Rb, Sr, Y, Yb, Cr, Ni, La/Yb and Sr/Y, they plot within adakitic fields. Furthermore, geochemical signatures e.g. the value of MgO, Cr, Th/Ce, Rb, Th and K2O/Na2O are better consistent with lower crust-derived adakitic melts. It is likely that during post-collisional stage (Neogene), slab break-off and asthenospheric up-welling was accompanied by delamination and thinning of overriding lithosphere. In this period, the mantle, and then after lower crustal mafics (the source of adakitic melt) are partially melted. The adakitic melts are probably more or less assimilated with mantle materials resulted in increasing some compatible element (like Ni) contents. Overall, chemical variation of Neogene magmatism in Azerbaijan area could be explained by the various mantle-crustal melt sources as well as crustal assimilation and fractional crystallization happened in post-collisional setting of Arabia- Eurasia plates.

The Alvand complex (Hamedan province) comprises several bodies ranging from acidic to intermediate and basic compositions intruded in the regional metamorphic sequence of the area (the Hamedan phyllites) during various magmatic episodes in Jurassic. In northern part of the complex (the Cheshmeh-Ghasaban area) there are some outcrops of hornblende gabbro and olivine gabbronorite. The olivine-gabbronorites are composed of olivine, clino- and ortho-pyroxene, plagioclase and hornblende. Apatite, magnetite, titano-magnetite, pyrite and chalcopyrite are the accessory minerals. The alterations include substitution of the olivine and pyroxene by bolingite, serpentine and chlorite. Electron microprobe analyses show that the amphiboles are of pargasite, and magnesio-hornblende. Variations of MgO, Al2O3 and Na2O and thermobarometry calculations based on amphibole and plagioclase compositions indicate that pargasites formed in average pressure and temperature of 11 kbar and 835°C, from metasomatized mantle derived melt as a result of asthenospheric mantle elevation and in extensional setting. Mafic magma contaminated with crustal material as it ascends. This situation can be provided in a rift setting (probably a back arc basin). Investigation of Fe and Ti concentration variations in the plagioclases indicates that differentiation trend of the parental magma was not consistent with concentration of these elements in the melt. High fO2 and slow cooling rate of the magma caused Fe-depletion during plagioclase crystallization. In addition, formation from a Fe-depleted source could be another factor that limited iron mineralization of the Cheshmeh-Ghasaban olivine-gabbronorite.

In order to study of calcareous nannofossils biostratigraphy, the upper part of the Pabdeh Formation and the lower parts of the Asmari Formation were selected in one well in Parsi oil field in southwest of Iran. Investigation of calcareous nanofossils in this section resulted in detection of 16 genera and 39 species. According to the first occurrence of index species and distribution of fossil assemblages, four biozones including Helicosphaera reticulate Zone (NP22/ Rupelian), Sphenolithus predistentus Zone (NP23/Rupelian), Sphenolithus distentus Zone (NP24/ Rupelian- Chatian) and Sphenolithus ciperoensis Zone (NP25/ Chatian), which is equivalent to zones CP16c - CP19b, was recognized in the upper part of the Pabdeh Formation. As a result of this study, and based on the identified calcareous nannofossil biozones, the age of the uppermost part of the Pabdeh Formation is Rupelian to Chatian. In the basal anhydrite portion of the Asmari Formation, no biozone of calcareous nanofossils was determined. In this study, the dominant conditions of the sedimentary environment, were determined by the presence of calcareous nannofossils index species, so that the presence of these species confirms the warm climate and basin location at low latitudes.

Reservoir petrophysical properties (including porosity, permeability and water saturation) are the most important characteristics of a hydrocarbon reservoirs that are used in economic evaluation, production planning and their development management. Accurate measurement of these properties is possible only by drilling wells and/or studying drilling cores, but by studying subsurface data (including petrophysical diagrams of drilled wells and reflective seismic information); we can find relations and based on them, estimate these reservoir properties for areas far from wells. In present study, the porosity of a part of the Qom Formation in the Aran anticline, located in Central Iran, is estimated using three-dimensional seismic data and porosity, density and P-wave sonic logs in three exploratory wells based on Model-based post-stack seismic inversion and using multi-attributes. The results show that the acoustic impedance indicator have the lowest error among the five used indicators. In addition, the amount of porosity in reservoir parts of the Qom Formation, between f and c₄ members,” from well A-01 toward well A-02 is more than well A-01 to well A-03.

In the southwest of Khuni mountain and the north of Kal-e-Kafi intrusion (northeast of Anarak), the igneous rocks of Khuni are cropped out. They dominantly show porphyritic texture and are similar to monzodiorite in composition. The phenocrysts mainly are clinopyroxene (diopside), amphibole (magnesiohastingsite to magnesian hastingsite), and feldspar (orthoclase in the rim and andesine in the core). Accessory minerals include primary biotite, apatite, sphene, and magnetite. The secondary minerals are biotite, calcite, epidote, tremolite- actinolite, and chlorite. Anti-rapakivi texture in feldspar is petrographic evidence of magma contamination. Application of various geothermobarometric methods for clinopyroxene and amphibole crystals in Khuni rocks yielded a crystallization temperature of ~1150°C for clinopyroxene and pressure range of 7-8 kb and temperatures of ~900-950°C for the amphibole phenocryst. Thermobarometry and chemistry of clinopyroxene and amphibole phenocrysts indicate that the rock-forming melt was formed by melting the continental crust in the Anarak area, as a result of the subduction-related magmatism of Eocene during the Neo-Tethys subduction beneath Central Iran.

Large benthic foraminiferas in Paleogene of Tethyan basin widley distributed that still remain poorly identified in the eastern Tethys specially in the southeastern of Iran. Based on systematic determination of LBFs 12 genera and 24 species in the Late Paleocene-Early Eocene interval are known that are Ranikothalia, Discocyclina, Miscellanites, Miscellanea, Kathina, Idalina, Assilina, Vania, Glomalveolina, Daviesina and Lockhartia. The base of SBZ3 biozone is defined by the first Occurence of Miscellanea juliettae, Miscellanites minutus, Miscellanites primitivus, Vania anatolica, Glomalveolina primaeva, Glomalveolina telemetensis, Glomalveolina dachelensis, Discocyclina seunesi, Ranikothalia sindensis, Ranikothalia tubleri, Kathina selveri. With respect to its high abundance and limited biostratigraphic range of above mentioned species (except Ranikothalia sindensis  and  Kathina selveri) can be taken as an index fossils of SBZ3. The base of SBZ4 biozone is defined by the first appearance of Discocyclina ranikotensis, Daviesins langhami, Miscellanea miscella which among them Ranikothalia  sindensis, Miscellanea miscella and Daviesina langhami appear in high abundance and widley distributed. It is mentioned that Miscellanites primitivus, in the studied section,is continued to SBZ5/6.SBZ5/6 biozone is defined  by Lockhartia haemei, Ranikothalia nuttalli, Ranikothalia sp., Assilina dandotica, Discocyclina dispansa and Discocyclina sella. Species of   Ranikothalia nuttalli, Assilina dandotica and Ranikothalia sindensis has high abundance and wide distributions. it is mentioned that in the some part of the eastern Tethys such as Tibet Daviesina genus has disappeared in the SBZ5/6 whilst in the studied sections has high abundance although  Alveolina vredenburgi  is not seen and Miscellanea miscella has low distribution regard to SBZ4. In the studied section, Earliest Eocene Large Benthic Foraminifera (SBZ5/6) predominantly consists of Ranikothalia and Miscellanea while the new Foraminifera assemblage that’s appear in the other locations (such as Assilina, Alveolina and Discocyclina) are less important and Nummulites are absent. In continuation of Early Eocene, gradual diversity of species of Discocyclina، Operculina and Assillina has occurred, whilst Ranikothalia is disappeared and Miscellanea  in the end of SBZ5/6 is less important. Similarity Larger Benthic Foraminifera assemblage in the other part of eastern Tethys especially India and Pakistan are recorded. Therefore this assemblage in the eastern Tethys are different from western Tethys.

Nowadays geomechanics plays a major role in optimizing the production and development stages of hydrocarbon reservoirs. The high cost of drilling wells and maintaining a functional well entails companies to utilize geomechanical modeling to determine the most efficient drilling path and the safest mud windows in order to maintain the stability of the well and prevent critical fracturing and collapses to occur. Using seismic data and well logs, one could estimate geomechanical properties such as elastic moduli, pore pressure, and especially the stress field of the reservoir. Knowledge of the stress regime present in the region of interest helps to determine the most suitable azimuth and inclination for drilling wells and estimating the mud weight window in order to optimize the drilling operation.In this article, in order to model the in-situ stresses and pore pressure, the regression of these values versus the acoustic impedances was obtained for the reservoir formation of an oilfield located south-west of Iran. The pre-stacked seismic data inverted for using well-log data to achieve the acoustic impedance values corresponding to the seismic horizon. The regression model for maximum and minimum horizontal stresses and the pore pressure obtained for a specific well. The regression models are then used to transform the inverted data to achieve a 3D model of the mentioned geomechanical parameters. The utilized methodology validated by comparing the modeled values for the geomechanical parameters and the corresponding values in the well. Then, based on the classification of Anderson fault theory, in one of the wells in the study area, the fault regime was determined as a Normal fault.

Zamanabad area is located in southern of Hamedan Province and belong to Sanandaj-Sirjan magmatic-metamorphic Zone. Lithologic units of this area comprising slate, phyllite, andalusite-garnet bearing schists, sillimanite bearing schists, hornfels, pegmatitic unit and recently alluviums. The most important of geological unit is Alvand granitoid pluton at age middle Jurassic. Presence of tourmalines with brown-green pleochroism and blue automorphic tourmalines such as probably indicolite is the specific features of tourmalines of Zamanabad area. Based on the microprobe analysis and multiple diagrams on tourmalines, the combination of tourmaline in granitic pegmatite is schorl and a few close to foitite. By the way, tourmalines in hornfels pegmatites are schorl and close to dravite. It was studied that tourmaline in granite pegmatites is alkaline and empty site whiles tourmaline in hornfels pegmatite is alkaline. Features such as automorphism, absence of chemical zoning, Al, Fe/Fe+Mg increase and decrease in X-site and host granite lack of Li and pegmatite and aplite related its show that these tourmalines have magmatic origin.Also, alkaline, without of X-site and further amount of Mg and a lesser amount of Al and Fe/Fe+Mg in tourmalines of hornfels pegmatites compatible to metapelites poor of Ca, metapesamites and tourmaline–quartz rocks show this complex have hydrothermal origin.

In this research, pyrophyllite phase transfer to tobermorite group and sodic to calcic zeolites was investigated in presence of NaOH and CaCl2 solutions. The experiments were carried out in three separate stages under constant hydrothermal conditions (temperature 150 °C, time 72 h) in the Teflon-lined autoclaves. The chemical composition of the initial sample was determined by XRF. Morphology and mineralogy of samples were characterized by SEM and XRD, respectively. The results showed that leucite and sodic zeolites (analcime, sodalite) were formed at variable concentration of NaOH (1–8 mol/l). The calcic zeolite was not synthesized in the presence of Na+ (1.5–2.5 mol/l) and Ca+2 (0.25-1 mol/l), but riversideite, hibschite, halite, hydroxycancrinite and trikalsilite were detected. Riversideite (a member of tobermorite group) and hibschite (a type of hydrogrossular) were formed at highest concentration of Ca+2 (1 mol/l), and halite was produced as a main product at lowest concentration of Ca+2 (0.25 mol/l). The concentration of Ca+2 and Na/Ca ratio are the main factors in the synthesis of these products.