نشریه زمین شناسی نفت ایران
سال دوازدهم شماره 1 (پیاپی 23، بهار و تابستان 1401)

In this research, the deposits of the Oligocene-Miocene Qom Formation in Kuh-e Charkheh (Natanz), Western Zefreh and Varton sections, northeastern Isfahan were studied. According to the field observations and thin section analysis in Carbonate part of the mentioned sections, 8 microfacies were identified, which were deposited from shallow part of lagoon to open marine and the sedimentary environment of 3 sections due to absence of reef and presence of bioclastic barrier and absence of spillage, the homoclinal carbonate ramp was detected. According to the sequence stratigraphic studies, each of the studied sections has two 3rd sequences. In Kuh-e Charkheh section, both sequences include of TST and HST, which are separated by sequence boundary SB2. In the western Zefreh section, the first sequence includes of TST and HST that is separated from the second sequence (include of LST, TST and HST) with sequence boundary SB1. In the Varton section, the first sequence is aggredation type and separated from the second sequence, which include TST and HST by a sequence boundary SB2.

Sarvak Formation is one of the important carbonate reservoirs in Dezful Embayment. In order to evaluate the reservoir quality of this formation in one of the Dezful Embayment fields, multi-resolution graph-based method was used and compared with petrographic findings. The findings showed that the Sarvak formation in the studied field consists of 8 microfacies belonging to the sub-environments of the lagoon, carbonate bar, middle ramp and outer ramp, which were deposited in a homoclinal ramp environment. The main diagenesis processes affecting this reservoir include cementation, dissolution, fracture, stylolitization, and dolomitization. The results of multi-resolution graph-based analysis led to the identification of 3 electrofacies, EF1 electrofacies had the weakest reservoir parameters and EF3 facies had the best reservoir status. The majority of EF1 microfacies are grainstone microfacies and the majority of EF3 microfacies correspond to wackstone and packstone microfacies. Based on this, it seems that the lagoon sub-environment has a better reservoir condition than other sub-environments, especially the carbonate bar, and this is an important sign of the different performance of diagenesis processes in these sub-environments. In a vertical trend, the highest volume of hydrocarbon column is in the EF3 electrofacies and the lowest is EF1. In general, it can be stated that the use of multi-resolution graph-based analysis and comparison with petrographic findings is a suitable solution for accurate evaluation of the reservoir quality of carbonate reservoirs.

In order to analyze the geochemical characteristics, the oil samples of the Asmari reservoirs and the Bangistan group in the Kopal field were studied using various geochemical techniques such as asphalting technique, gas chromatography technique, gas chromatography-mass spectrometry technique and carbon isotope measurement technique, were subjected to analysis. the purpose of This research is a comparison of carbon isotope and geochemical properties of Asmara and Bangestan oils in Kopal field to determine their parent rock and origin. Considering the results of the testing technique and analysis of biomakers of the esteranes and terpanes family extracted from saturated cutting, it can be stated that the oils accumulated in the Asmari and Bangestan reservoirs of the Kopal field have the characteristics of oil. are paraffinic, which indicates the existence of light oil with good quality, mature, low viscosity and high sulfur. By placing the ratio of biomarker parameters against carbon 13 isotope and examining the general results of the graphs, it was found that the oil samples of Asmari reservoirs and Bangestan reservoirs in the studied field are from a common generative rock. have been found and have the same characteristics and only slightly differ in maturity, degree of fluidity, and the amount of migration processes between the source rock and the reservoir rock, and similarly, the transformation course of the source rock organic materials has occurred naturally in the Copal field. The values of carbon isotopes in the oils indicate the average maturity of the rocks producing the oils. The graph of the ratio of the aromatic carbon 13 isotope against the saturated carbon 13 isotope showed that both field oil samples The subject of study belongs to marine environments.

Esfandiar field is located at the northern part of the Persian . This field is a single large anticline with Lulu field of Saudi Arabia, with , 20 KM length and 7 KM width. The field was discovered in 1966 by drilling of well E1, on the northern culmination of the field. wells E3 and E2 were drilled at the top of structure in the southern part of the field. DSTs tests results of E1 proved that the top of Lower Ratawi formation contain 15 m oil column. E3 well test result regards as a dry hole DSTs test results of E2 were not conclusive due to inadequate testing plans . E4 Appraisal well contained, 14 m oil column at the Lower Ratawi. Log interpretations results indicated, E2 and E3 wells contains oil in Yamama formation in the southern part of the field which has not been tested properly. Lower Ratawi (Top oil-bearing zone ), Zone 'B' of Lower Ratawi (Oil bearing zone at bottom), Yamama were constructed based on the existing data. Petrophysical and geophysical data has been used for the Lower Ratawi reservoir, as a result the geological models (structural and porosity models), with applying, related software’s and neural network geophysical method are generated . At the conclusion, the recommended plan consists of horizontal drilling wells for oil production in Lower Ratawi in the north of the field has been proposed.

Carbonate successions are considered archives for recording the palaeoclimatic proxies and so they are suitable for understanding climatic patterns and identifying the Milankovitch cycles and cycles’s impacts on sea-level changes during Phanerozoic. In the current study, the carbonate successions of the Ilam Formation (Santonian) and their spectral gamma-ray data were chosen to identify the cycles and influencing factors on the sedimentation in one of the oilfields in the Dezful Embayment, southwest of Zagros mountains. According to available evidence, all of Milankovitch cycles contributed to changes in climatic conditions simultaneously with development of the Ilam Formation, however, the long Eccentricity cycles were dominant and have played a greater role in this issue. The sedimentation rate was estimated at 4-5.5 cm/kyr on average in the Ilam Formation. Considering the sedimentation rate and number of identified long Eccentricity cycles, it could be said the deposition in the Ilam Formation lasted in 1.13-1.8 Ma. Our results indicate that the relative sea-level changes in the studied wells correspond to the eustatic sea level. The deposition process in the Ilam Formation was largely affected by the performance of long Eccentricity cycles, eustatic sea level, and tectonic events during the Upper Cretaceous.

Shally units are one of the most problematic parameters in the process of drilling oil reservoirs. The current study is related to the instability of the wellbore due to the presence of clay minerals bearing shally units of the Pabdeh-Gurpi formations in Aghajari oilfield. Investigation and identification of shales were done using the XRF laboratory and NGS logs. The results showed that the NGS method is sensitive and applicable to identify Illite mineral merely. According to Fe2O3 content, the upper part of the oxidant conditions, but towards the Gurpi, is dominated by reduction condition. The role of other elements in the formation of clay minerals was discussed. Based on the amount of iron, manganese and vanadium, the samples are classified as the Quinby_Hunt and Wilde class lll (non-sulfide resuscitation but Eh recovery and medium to low pH). The range of changes in the Th/U ratio (4-1.5) signified an environment with changes from sea to intermediate states.