GEOPERSIA
Year:2015 | Volume:5 | Issue:2|Papers Count:8

Middle Jurassic fluvio-deltaic and turbiditic mudstones of the Kashafrud Formation are important hydrocarbon sources in the gas-rich Kopet-Dagh Basin, northeastern Iran. Clay mineral assemblages are important for the interpretation of sediment provenance and for understanding burial diagenetic cementation in sandstones. The clay mineral assemblages in fluvio-deltaic and turbiditic mudrocks in two areas, Saleh-Abad and Senjedak, were investigated by X-ray diffraction analysis. A total of 28 bulk samples (half of which were taken from Saleh-Abad and the other half from Senjedak) were analysed and from 11 of these samples the<2 mm fraction was separated and analysed. The clay minerals identified are mostly kaolinite, illite, muscovite, chlorite, mixed-layer illite-chlorite, and very rarely smectite. Clay mineral assemblages result partly from variable detrital supply and partly from burial diagenesis. Detrital muscovite is more abundant at higher stratigraphic levels. Detrital smectite was rare; the lack of detectable illite-smectite mixed layer clays indicates that low smectite abundance is not the result of illitization. Vitrinite reflectance suggests burial to depths of only 2–3 km. Burial diagenesis resulted in more chlorite and more ordered mixed-layer chlorite-illite at greater burial depths. The source area for the basin was a rapidly rising area that included illitic shales, overlying crystalline basement of granite, and low-grade metamorphic rocks, which supplied muscovite and chlorite.

Lithofacies identification can provide qualitative information about rocks. It can also explain rock textures which are important components for hydrocarbon reservoir description Sarvak Formation is an important reservoir which is being studied in the Marun oil field, in the Dezful embayment (Zagros basin). This study establishes quantitative relationships between digital well logs data and routine petrographic data, obtained from thin sections description. Attempts were made to predict lithofacies in 13 wells, all drilled in the Marun oil field. Seven well logs, namely, Gamma Ray (SGR and CGR), Deep Resistivity (RD), Formation Density (RHOB), Neutron Porosity (PHIN), Sonic log (DT), and photoelectric factor (PEF) as input data and thin section/core-derived lithofacies were used as target data in the ANN (artificial neural network) to predict lithofacies. The results show a strong correlation between the given data and those obtained from ANN (R2=95%). The performance of the model has been measured by the Mean Squared Error function which doesn't exceed 0.303. Hence, neural network techniques are recommended for those reservoirs in which facies geometry and distribution are key factors controlling the heterogeneity and distribution of rock properties. Undoubtedly, this approach can reduce uncertainty and save plenty of time and cost for the oil industry.

The investigated section cropping out in Kuh-e-Banesh, Zagros basin (southern Iran) is represented by limestone, Cherty beds and marl levels bearing abundant Planktonic foraminifers, radiolarian microfaunas, and ammonite imprints. For the first time, well to moderately preserved forms of Planktonic foraminifera have been extracted from black shale and marls levels. Extracted biota was studied with regard to relationship with abundances of radiolarian and total organic carbon. Rock Eval analysis shows high total organic carbon content within Daryian Formation (lower part). The presence of high abundances of planktonic foraminifers and radiolarian associated with high total organic carbon content in the lower part of the Dariyan Formation suggest a high productivity event, eutrophication, and warming phenomena of the ocean during early Cretaceous. Biostratigraphical ranges of planktonic foraminifera in the studied section indicate Early Aptian to early Late Aptian age. It is, therefore, implicated that the oceanic anoxic event 1a (OAE 1a) interval be regarded as equivalent levels in Tethys domains. The black shale of oceanic anoxic event is characterized by the widespread existence of regionally organic-rich beds in the Tethys basins. Micro-paleontological and geochemical results provide new insights into the paleogeography of the Tethys realm and better correlation with well-studied worldwide successions.

Fractures are considered as one of the important structures in fractured reservoirs due to their effect on fluid currents and reservoir parameters such as porosity and permeability. Fracture parameters can only be directly calculated with core and image logs. Cores have serious limitations, so image logs are the best method. The aim of this study is the systematic fractures analysis of the Asmari Formation in the Marun field as one of the giant oilfields in world. The main objectives of image logs were evaluating structural dip, characterizing natural fractures and field structure heterogeneity, and finally correlating the results with complimentary methods such as Velocity Deviation Log (VDL), Repeat Formation Test (RFT), mud lost data, and isodip map in the carbonate Asmari Formation. Generally, electric and ultrasonic imaging tools record vast amounts of high-resolution data. This enables geoscientists to describe in detail the structural fracture networks. The results indicate that the highest fracture density is in the zones 1, 20, and 30 of the Asmari reservoir that show high correlation with VDL and mud lost data. Image logs also show a range of bedding dips from 20o in the northern limb to 30o in the southern limb with strikes ranging from 10 o to 270 o N. Regarding the general pattern of fractures, it is evident that they are related to the folding and are classified mainly as longitudinal, transverse, and oblique. The longitudinal pattern is dominant and often forms open fractures. They are characterized by N50W-S50E and mainly observed in the upper Asmari zones. Moreover, to find the vertical relation of the layer and fractures, RFT data were used. The findings revealed the presence of a vertical relation in the upper horizons of the reservoir, especially in the eastern section due to the high fracture density.

This research investigates the changes of soil properties in Dasht-e Abbas plain due to the Karkheh water transfer to this plain. In this study, the maps of groundwater level changes before and after the utilization of irrigation system were prepared. Furthermore, to investigate the changes of soil characteristics, soil samples were collected from various project implantations and control areas and their parameters were determined and compared. The results showed that the groundwater level has been increased more than 15 meters during the study period and the depth of groundwater in some areas reached to less than 5 meters. The results indicated that the highest salinity belonged to the network coverage areas and evaporating zone having a saturation extract electrical conductivity of 10.62 and 9.26 ds/m respectively, while dry land areas have the lowest salinity with electrical conductivity of 0.8- 4.0 ds/m. The results further demonstrated that the water transfer of Karkheh Dam to Dasht-e Abbas due to the absence of drainage in 3 and 4 sub-networks, high volume of agricultural return water from flood irrigation, and inadequate development of groundwater exploitation has reduced the quality of soil in marsh area and flooding lands, and generally a "desertification" process after "combat to desertification" has occurred.

In recent years, the nanoscale zero-valent iron (NZVI) particles have been used successfully for the degradation of hydrocarbon compounds and remediation of other pollutants. Nevertheless, as far as we know, there is no specific study on the improvement of the geotechnical properties of contaminated soils with hydrocarbon compounds by NZVI. This study used NZVI particles to remove gas oil in a clayey soil and determined the effects of NZVI on Atterberg limits, compaction properties, and shear strength parameters of the soil. In order to determine the optimal reaction time and NZVI dosage, the total organic carbon (TOC) of a contaminated soil with 9% of gas oil was measured. The experimental data showed that the optimum reaction time and NZVI dosage were 24 days and 5%, respectively. Then, the contaminated samples were prepared by mixing the soil with gas oil in the amount of 0, 3, 6, and 9% by dry weight. The results showed a decrease in the friction angle (j) and an increase in the cohesion (C). Maximum dry density and optimum moisture content of the soil decreased due to the contamination. In addition, an increase in liquid limit (LL) and plastic limit (PL) were observed. Finally, all contaminated specimens were mixed with 5% of NZVI. After 24 days, an increase was seen in the friction angle, cohesion, maximum dry density, and optimum water content. LL and PL of the soil decreased after the treatment.

This study investigates the correlations among the tensile strength, mineral composition, and textural features of twenty-nine sandstones from Kouzestan province. The regression analyses as well as artificial neural network (ANN) are also applied to evaluate the correlations. The results of simple regression analyses show no correlation between mineralogical features and tensile strength. However, the tensile strength of the sandstone was decreased by cement content reduction. Among the textural features, the packing proximity, packing density, and floating contact as well as sutured contact are the most effective indices. Meanwhile, the stepwise regression analyses reveal that the tensile strength of the sandstones strongly depends on packing density, sutured contact, and cement content. However, in artificial neural network, the key petrographical parameters influencing the tensile strength of the sandstones are packing proximity, packing density, sutured contact and floating contact, concave-convex contact, grain contact percentage, and cement content. Also, the R-square obtained ANN is higher than that observed for the stepwise regression analyses. Based on the results, ANN were more precise than the conventional statistical approaches for predicting the tensile strength of these sandstones from their petrographical characteristics.

The Olang area is a part of Gheshlagh-Olang synclinal, which is a member of eastern Alborz coal basin and is situated at a distance of 70 km northeast of Shahroud city. Coal-bearing strata of this region are part of the Shemshak group (Upper Triassic to Lower Jurassic). Samples from the 9 coal seams of the Olang coal deposits were collected and ashed. The aim of this study is to determine the occurrence and distribution of major and trace elements in the coal ashes of Upper Triassic Olang coal deposits in northeastern Iran. The concentration of the elements in the coal ashes of the Olang region is higher than the Clarke value and the average of World coal ash. The coal ashes have been enriched in Zn, Mn, and P in comparison with the average of the World coal ash. The correlation coefficient analysis on the major and trace elements in the ash yielded in four groups including: A (Rb, K, Cs, Si), B (Al), C (Tl, Ca, Nb, Ta, V) and D (Cr, Hf, Sn, Zr, Th, Zn, Ti, Ba, W, Mg, Na, P, Sr, Co, Cu, Mo, Ni, U, Fe, Ca). The first two groups are strongly correlated with ash yield and mainly have an inorganic affinity. C and D groups are negatively or less strongly correlated with ash yield. The rare earth elements' abundances are negatively correlated with the ash yield and exhibit an organic affinity. Based on correlation, cluster analyses, and rare earth elements' distribution characteristics, two separate modes of occurrence can be considered for rare earth elements: 1) Accompanying phosphate minerals with organic origin (phosphorites) or phosphate organic materials, and 2) Accompanying the vitrinite maceral group.