Iranian Journal of Earth Sciences
Volume:13 Issue: 3, Jul 2021

A new exploration technique called Thorium Normalisation Method has been applied on the airborne radiometric data of the Bornu basin and its environs to delineate favourable zones for hydrocarbon accumulations within the study area. This method is significant because it indicates the probable presence of hydrocarbon in a sedimentary basin. Separation of the radiospectrometric measurements over each lithologic unit and the estimation of the characteristic statistics of these units were carried out. The statistical treatment applied on the radioelements (K, eTh and eU) of the study area shows a relatively low coefficient of variability (CV%) value for K, eTh and eU signifying their high degree of homogeneity.  The mean value of the radioelements (K ranging from 0.6 to 2.0 %; Th ranging from 9.6 to 15.9 ppm and U ranging from 2.2 to 3.8 ppm) obtained from the statistical analysis correlates with the mean of natural radioelement (K ranging from 0.1 to 2.7 %; Th ranging from 0.4 to 11.2 ppm and U ranging from 0.1 to 3.7 ppm) content of sedimentary rocks which corresponds to shale, the main source rock for hydrocarbon accumulation in the study area. The DRAD (delineation of radioactive anomalies) result ranges from -0.77 to 1.83. The positive values are indicators of favourable zones for the presence of hydrocarbon accumulations. These results suggest that the preliminary information obtained from the use of the thorium normalisation method will guide the exploration of hydrocarbon in the study area.

The Eastern Suleiman Fold and Thrust Belt comprises of a thick cover of sedimentary sequences. Despite of presence of complete petroleum system source, reservoir and seal rocks less attention was paid by the exploration and production companies to prospect. An integrated approach is adopted to delineate reservoir potential and net pay zones in the clastic reservoirs of the Cretaceous age widely distributed in the area. Wireline logs and migrated seismic reflection data were used for field development and optimization. Petrophysical analysis reveals that Pab Sandstone of the Cretaceous age is acting as a reservoir rock, whereas the Ghazij Shales of the Eocene age are acting as a regional seal rock. A complete workflow is proposed for formation evaluation, and structural interpretation of the subsurface geology. Based on wireline logs it is interpreted that the thickness of the Pab Sandstone varies from 250 m to 350 m in the entire study area. The sandstone is massive with high porosity and intercalated layers of shales. Faulted anticlinal structures are present in the study area which are favorable for the accumulation of hydrocarbon. 3D structural models and various seismic attribute models were prepared to analyze the reservoir character of this clastic reservoir. Based on wireline logs and seismic data clean sand, shaly sand and shale are marked as dominant facies in the study area. However, clean sand facies are more favorable to act as potential net pay zone.

Core data analysis of one well from the Karanj oil field, southwestern Iran, allowed us to precise the biostratigraphy, microfacies and paleoecology of the Asmari Formation. Analysis of thin section from this cored well permitted identification of 28 genera and 20 species of benthic and planktic foraminifera respectively. Subsequently four benthic foraminiferal assemblage biozones were identified, as follows: (1) Lepidocyclina-Operculina-Ditrupa Assemblage zone, (2) Archaias asmaricus-Archaias hensoni-Miogypsinoides complanatus Assemblage zone, (3) Miogypsina-Peneroplis farsensis–Elphidium sp. 14  Assemblage zone and (4) Borelis melo curdica-Borelis melo melo Assemblage zone; indicating an Oligocene (Rupelian-Chattian) to early Miocene (Aquitanian to Early Burdigalian) age for the Asmari Formation. Microfacial study of depositional textures led to characterizing 12 microfacies types, indicating environments in five different settings: restricted lagoon, open lagoon, shoal, slope, and basin mostly in the upper Asmari Formation. These sediments had been deposited under 3 different salinity levels (from 34 to more than 50 psu) in an environment ranging from aphotic to oligophotic and to euphotic zones, and under oligotrophic to eutrophic conditions from the Chattian to the Burdigalian on a carbonate platform (homoclinal ramp). In the studied well, the Asmari Formation had been deposited in a marine environment with normal salinity during the Rupelian-Chattian interval and in a marine environment with high salinity during the Aquitanian to the Burdigalian times.

Hydrogeochemical characteristics of groundwater and its suitability for domestic and irrigation, purposes were evaluated in Konaro ophiolitic area. Heavy metals pollution is accounted for a major pollution in the natural environment are that can pose a serious threat to ecosystems because of their biodegradation potential, toxicity and sustainability (Moslempour and Shahdadi 2013) 8 representative groundwater samples were collected from wells and qanat and analyzed for major cations and anions. The order of dominance of cation and anions were Na> HCO3> SO4 > Mg> Cl> Ca> K, respectively. The rock weathering and dissolution of minerals processes, especially ophiolitic rocks minerals are dominant in controlling the groundwater quality in the study area. Electrical conductivity (EC) and total dissolved solid (TDS) show high positive correlation with total Hardness (TH), K, Na, and SO4-. As per the WHO standards for domestic water purposes, majority of samples show that the groundwater is suitable for drinking. The spatial distribution maps of physicochemical parameters were prepared in ArcGIS. The suitability of groundwater for agriculture purpose was evaluated from EC, TDS, sodium adsorption ratio (SAR) and Na% which ranges from excellent to not suitable, so majority of the groundwater samples are suitable for irrigation. The results revealed that the GQI quality index varied between 89% and 91% in the Konaro area, which in terms of quality rating, the water samples from these resources laid in appropriate to acceptable range. Moreover, based on examining the zoning map, the GQI quality index accounted for the lowest value in the east direction of the study area. Thus, most of the groundwater samples from this study (sample W2) confirm the beneficial use of aquifers in the area for domestic, agricultural, and irrigation purposes.

In the current study, we have developed a new method called the third- order moving average method to estimate the shape and depth of residual magnetic anomalies. This method, calculates a nonlinear relationship between depth and shape factor, at seven points with successive window length. It is based on the computing standard deviation at depths that are determined from all residual magnetic anomalies for each value of the shape factor. The method was applied to the synthetic model by geometrical shapes both as horizontal cylinder and combination of horizontal cylinder, sphere and thin sheet approaches, with and without noise. It was tested by real data in Geological Survey of Iran (GSI). In this study, least square methods were applied to interpret the magnetic field so that we can compare the results of this methods with the third- order moving average method. This method is applied to estimate the depth using second horizontal derivative anomalies obtained numerically from magnetic data with successive window lengths. This method utilizes the variance of the depths as a scale for calculation of the shape and depth. The results showed that the third- order moving average method is a powerful tool for estimating shape and depth of the synthetic models in the presence and absence of noise compared to least square method. Moreover, the results showed that this method is very accurate for real data while the least square method did not lead to feasible results.In this study, least square methods were applied to interpret the magnetic field so that we can compare the results of this methods with the third- order moving average method. This method is applied to estimate the depth using second horizontal derivative anomalies obtained numerically from magnetic data with successive window lengths. This method utilizes the variance of the depths as a scale for calculation of the shape and depth.The results showed that the third- order moving average method is a powerful tool for estimating shape and depth of the synthetic models in the presence and absence of noise compared to least square method. Moreover, the results showed that this method is very accurate for real data while the least square method did not lead to feasible results.

In the easternmost part of the Izeh Zone of the Zagros Mountains, the Kazhdumi Formation of upper Aptian-middle Albian interval is superbly exposed in three-main exposures as argillaceous carbonate facies. The main bioclastic components of the Kazhdumi Formation are Orbitolinid and other larger benthic foraminifers, planktonic foraminifera and calcareous algae. The depositional system in the study area during the upper Aptian-middle Albian corresponds to a shaly carbonate ramp. Two depositional sequences are determined, as prograding system from west to east. Comparison of the proposed depositional sequences with those reported in the Arabian Plate and adjacent areas suggests a correlation with the global sea-level curve. The Lower Cretaceous, Aptian carbonates of Kazhdumi Formation contain nine microfacies, which were deposited on a ramp system deepened in both directions (west and east). Stratigraphic sequence led to recognize two third-order sequences. On the other hand, rudstone and boundstone lithofacies of the studied formation have higher reservoir potential and were deposited during Apt 3 and Apt 5 sequences of the Arabian Plate. The Kazhdumi Formation in the study area was deposited in an intrashelf basin that should be classified as an independent basin in the future paleogeographic maps of the southwest Iran. We interpret the Kazerun Fault, as a crustal warping of basement faults of the Arabian Plate boundary, which were responsible for the creation of the intrashelf basin in the study area.