نشریه زمین شناسی نفت ایران
سال یازدهم شماره 2 (پیاپی 22، پاییز و زمستان 1400)

Kale-Sardar section, is located at the vicinity of Niaz village, 15 kilometers east of Tabas town. This section consists of 80 m thick and from Late Devonian deposits as known as Shishtu formation that upper part of this section has cut by a fault by Frasnian’s deposits. The entire studied thickness is subdivided into 12 lithostratigraphic units and in order to study of conodont elements, 27 species and subspecies belonging to 7 genera were recognized, that due to these revealed conodont elements, Shishtu formation’s age in the studied section spans from Eifelian to late Frasnian. The Frasnian-Famennian bio event in studied section is located between two intervals linguiformis Zone and Lower to Middle triangularis zones which is located at the top of the dark Frasnian shales and at the base of the thin limestones of the Famennian layer. The microfacies determined in studied section are subdivided into siliciclastic-carbonate and carbonate facies, which were deposited from the shore to the deep part of the marine environment. Gradual changes in facies within stratigraphical sequence, sedimentological hiatus due to sudden change in sedimentary environment’s slope, absence of reef facies (related to Wilson’s 5th facies zone) and presence of discontinuous bioclastic barrier (existence of semi-enclosed lagoon), convey that studied sediments were deposited in a homoclinal carbonate ramp.

The aim of this study is geochemical evaluation of the Fahlian, Gadvan, and Surmeh formations as possible source rocks in Gachsaran oil field using Rock-Eval Pyrolysis manner. All of the studied samples possess migration index amounts lower than 1.5 showing indigenous nature of their hydrocarbons. TOC versus S2 and TOC against S1+S2 diagrams suggest fair hydrocarbon generation potential for the Fahlian and Surmeh formations and fair to good potential for the Gadvan formation. for the Fahlian and Surmeh formations type III kerogen and for the Gadvan formation mixed type II and II-III kerogens were identified. So, the Fahlian and Surmeh formations contain organic matter with terrigenous source (gas prone) and the Gadvan Formation possess both of marine and terrigenous organic matter (oil and gas prone). According to the cross plot of Tmax versus Hydrogen index (HI), the Gurpi formation is capable of mixed gas and oil, and gas generation and the Fahlian and Surmeh formations considered only gas prone formations. In terms of organic facies type, the surmeh, Fahlian, and Gurpi formations located in CD, C and CD, and BC and C zones of jones diagram, respectively. So, the Gadvan formation in compare to the Fahlian formation and the Fahlian formation in compare to the Surmeh formation, deposited under more anoxic conditions. In terms of thermal maturity, All of the Fahlian, Gadvan, and Surmeh formations located in oil window zone, but the Surmeh formation possess higher maturity than the Fahlian formation and the Fahlian formation have highr maturity in compare to the Gadvan formation.

Permeability in fluid flow is for a porous rock, which is exactly what causes the problem. core analysis and well testing are two most commonly used methods of permeability measurement, but in-vitro measurement of permeability by applying core analysis on all wells in a specific field is very time consuming and costly and even impossible when dealing with Horizontal wells. Wells testing, on the other hand, is not cost-effective for reasons such as; High costs and zero production during the testing process. Therefore, thanks to their low cost, comprehensiveness and availability, permeability estimation methods developed according to conventional logs land DSI diagrams are of critical importance. Taking this into account, in the present study, permeability was first estimated using multi-resolution graph-based clustering (MRGC) and the results were compared with permeability rates obtained from core analysis. In the second stage, permeability was measured by ST-FZI method and the results were compared with permeability rates obtained from core analysis. In the third stage, the multi-resolution graph-based clustering (MRGC) method was used to improve the permeability calculated by the ST-FZI method and overcome the reservoir heterogeneity. First the flow units were identified, and then the ST-FZI method was applied on each flow unit to calculate permeability and finally the calculated permeabilities were combined to obtain an accurate permeability graph of the studied well. The correlation coefficients of permeability rates estimated via core analysis in the multi-resolution graph-based clustering method (R2 = 77), ST-FZI method (R2 = 47) and improved method (R2 = 84) were measured. The afore-mentioned method was able to improve the permeability calculated in the previous step by 37% and was recognized as the best permeability measurement method in the Kangan reservoir of the well subjected to study.

The only outcrop of Asmari formation in the Dezful embayment is visible in the Asmari anticline. In order to estimate the strain parameters and shortening values, 26 geological cross sections were prepared perpendicular to the anticline axis. Based on the, interlimb angle measurements, the interlimb angles of the northern and central parts of the anticline show smaller angles than the southern parts. Determination of strain ratio (R) values indicates the strain values between 1.12 - 1.52. The zoning map of strain ratio values shows higher strain values in the northern and central parts of the anticline. Using geological cross sections and measuring the base length of the folded layer of Asmari formation (L0) and the straight length of the layer (L1), the percentage of shortening values were calculated in each section. The results show the occurrence of 1.8% to 12% shortening in different parts of the anticline. Shortening map of the Asmari anticline shows more shortening amounts in the northern and central parts of the anticline than the southern parts.

After the Late Cretaceous and during the Paleogene, with the sea level rising, the Zagros sedimentary basin is covered with a progressive sea in which the Pabdeh Formation is deposited. The dual function of this formation as a source of oil and its reservoir capacity due to the diversity of lithology and its location between the two reservoirs Asmari and Bangistan, and the age of this formation is one of the issues that has attracted the attention of geologists. In order to study the stratigraphic and biostratigraphic rock of the Pabdeh Formation, the Jahangirabad section in the northwest of Zagros sedimentary basin has been selected and sampled. 320 samples were taken, of which 230 samples were prepared by washing method, and 90 samples were prepared by thin section method and examined. Based on studies conducted in the Jahangirabad section, 25 genera and 110 species have been identified, and based on the identified fossils, 27 biozones and 7 sub-biozones have been identified. Based on the identified biozones, the age of the Pabdeh Formation in the Jahangirabad Danian Early-Late Chattian section has been obtained. Pabdeh Formation deposits in the Jahangirabad section have a thickness of 676 m (beginning of purple shale to anhydrite Kalhor) which includes units of purple shale (2 parts), marl limestone with lower limestone, limestone, and marl limestone with limestone It is high. In this section, the lower boundary of the Pabdeh Formation is continuous with shales and marls of Gurpi Formation, and its upper boundary is with continuous limestone of Asmari Formation.

The sedimentary basin of Kopeh-Dagh is located in the northeast of Iran. This sedimentary basin has been of interest for a long time because of hydrocarbon materials. Gavelinellids are the most abundant and dominant groups of benthic foraminifera in epicontinenal seas during Cretaceous period which belong to Rotaliinacean foraminifera. They have shown a wide biogeographical distribution and dispersion in many areas of Tethys. Their evolutionary trend during the Cretaceous time was success. The high concentration of marine sedimentary rocks and the absence of igneous activities in the Kope-Dagh sedimentary basinhave caused it to be considered the most suitable basin for the formation and accumulation of hydrocarbons after the Zagros sedimentary basin. This basin has suitable layers of carbonate rocks and porous sandstones to store hydrocarbon materials, also thick layers of shales in this basin can act as suitable source and cap rocks. In this research some genera and species from this family in Sanganeh and Aitamir Formations at five stratigraphic sections including Marave Tappeh, Takal kuh, Sheykh, Gadvecanlou and Kalat from point of biostratigraphical and paleoecological applications have been investigated. In this study, four biozones including Gavelinella flandrini-Gaudryina cf. praedividens assemblage zone, Berthelina intermedia assemblage zone, Berthelina cenomanica Assemblage Zone, Berthelina intermedia-Osangularia schloenbachi Assemblage Zone have been introduced. Based on the reported genera and species of the Gavellinidae family, it can be stated that the studied formations were deposited in the middle and outer part of the continental shelf to the upper part of the continental slope and in aerobic to semi-aerobic environments. The presence of more planktonic foraminifera than benthic foraminifera in the Aitamir Formation, the depth of the basin increases.