نشریه زمین شناسی نفت ایران
سال دوازدهم شماره 2 (پیاپی 24، پاییز و زمستان 1401)

The Ordovician marine sedimentary sequences of Iran are located in different structural blocks along the northern margin of Gondwana. In the north of the Kerman Basin, Ordovician sedimentary sequences named Katkoyeh Formation have been introduced, which consist of 70 to 300 meters of siliceous siliceous rocks, one or two thin carbonate horizons in the upper part, and pyroclastic deposits. Traditionally, the Cambrian-Ordovician boundary in the Kerman Basin has been determined between the Hatken Dolomite Member of the Kuhbanan Formation (Late Furongian) and the Lower Shale Member of the Katkuye Formation. However, determining the location of the previous Tremadocine boundary is uncertain because no fossils have been documented from this interval. For the purpose of biostratigraphy of the Katkuye formation in Kerman basin, Gezoye section with an approximate thickness of about 170 meters was selected. In this section, the Katkoyeh Formation is located on the Hatken Dolomite Member and under the Shabjareh Formation sandstones of Silurian age. In the Gezoiye section, due to the action of basalt dikes and intense tectonics in the region, the limestone layers containing fossils have been severely altered, and during three sampling stages, 320 conodonts were recovered from the carbonate horizon of the upper part of this formation, and 3 Genus and 7 species were identified and based on this, three conodont ranges were recorded: 1) Icriodella superba Range Zone (Katian - ? Hirnantian; Late Ordovician), 2) Amorphognathus ordovicicus Range Zone (Katian - Late Ordovician), 3) Amorphognathus superbus Range Zone (Katian - ? Hirnantian; Late Ordovician). Late Ordovician age in the Katkuye formation in the Gezoye section with at least three species of the conodont genus Icriodella (I. superba, I. deflecta, (I. cf. discrete and two species of A. superbus) Amorphognathus, A. ordovicicus) determined and led to the identification of the Katian-?Hirnantian rocks.

Asmari Formation (Rupelian-Burdigalian) is one of the most well-known formations in Iran. In order to investigate the stratigraphy and sedimentary environment, a section of this formation was selected in Khamir salt mountain section in Bandarlengeh embayment. In this number, 70 limestone microscopic thin sections and 3 marl samples (XRF) were evaluated to identify the microfacies and the sedimentation conditions.The petrographic study led to the identification of 10 microfacies belonging to the facies belts of tidal, lagoon, carbonate bar, open marine, which were deposited in the homoclinal carbonate ramp environment. The composition of marl facies oxides also indicates the presence of carbonate minerals, quartz and clay minerals, which along with field observations and alternating calcareous facies suggest that this facies was deposited in an open marine environment. Finally, it seems that the facies and fossil diversity of the Asmari Formation in the mentioned section is such that during the Aquitanian stage, this formation was located closer to the coast line and during the Rupelian and Chattian-Burdigalian times, it was located at a further distance from the coast line.

Sarvak formation is a major oil reservoir in the Persian Gulf. Various nomenclature of the Sarvak formation were applied by different operative oil companies In the northern part of the Persian Gulf. The aim at this study is to harmonize stratigraphical nomenclature in this district , as well as to study the reservoir qualities and to asses hydrocarbon accumulations in this area. By using different petrophysical data and integration with geological factor, resulted in revealing three stratigraphy members ( Mishrif, Ahmadi and Mauddud), as well as reservoir qualities variations , in this district. By applying, available petrophsical data, and integration with geological information, various 3D geological maps, ( porosity, water & oil saturation maps etc…) were made. Preliminary assessment of the reservoir potential of the Bahregansar & Hendijan Fields shows , Sarvak formation in these two fields, have a good reservoir qualities, but other part of this district has poor reservoir qualities. This study shows , having high portions of clay mineral in the Sarvak reservoir along with lack of suitable cap rock and poor reservoir qualities , diminished reservoir potentials in this district.

The Bangestan reservoir of Zeolaie oil field consists of Ilam, Surgah and Sarvak formations and divided into 8 zones. To construct 3D model (structural and petrophysical) needs to input the software all interpreted geophysical data, graphic well logs, and 2D maps of the reservoir and control their quality. Structural model are provided using the surfaces of top formations and well pick data. These data are input the software directly/indirectly with high potential griding process to make interpreted surfaces. Isochore map of Ilam Formation was digitized as an interpreted surface and input the model as the base contour map. Other isochore maps were plotted using the well picks and entrance depths of the reservoir zones. To provide the petrophysical model reservoir characteristics were evaluated and average porosity, and water saturation % maps provided. These maps revealed that the reservoir characteristics are improved from SE to NW in the oil field.

In this research, the process of lithological changes and diagenetic processes of Asmari formation with Oligo-Miocene age has been investigated. For this purpose, 400 samples were selected and collected from a section of the Masjid Suleiman oil field and the surface section of the Asmari anticline in the Dezful depression and the Gurpi anticline in the Izeh zone. Petrographic studies revealed 18 sedimentary microfacies that were deposited on a ramp-type carbonate platform. Among the significant diagenetic processes in the region are the process of micritization, bioturbation and the influence of burrowing organisms, cementation (types of cement related to marine, meteoric and burial diagenesis environments), dissolution (meteoric and burial dissolution), dolomitization (in different phases), silicification, pyritization, phosphatization, mechanical compaction, chemical compaction, fracture and porosity. Based on the identification of the sequence boundaries and following the facies depth changes, the carbonate sequence of the Asmari formation in the subsurface section and the Asmari anticline section are introduced in the form of 3 sedimentary sequences of the third order shallowing upwards, which are the former Aquitanian, the late Aquitanian and Bordigalin belong. Among the dominant porosities in the Asmari Formation, we can mention the hole, mold and fracture porosities.

Zagros Sedimentary basin is located in the south and southwest of Iran and Pabdeh Formation is one of the most important Cenozoic units of Zagros Sedimentary basin. In addition, Pabdeh Formation is of special importance as one of the source rocks of Zagros Sedimentary basin. In order to study the Lithostratigraphic and Biostratigraphic rocks of Pabdeh Formation, the section of Ilam dam in the northwest of Zagros sedimentary basin has been selected and sampled. 360 samples were taken, of which 260 washing samples and 100 thin section samples were prepared. Based on the studies performed on these samples, 25 genera and 105 species have been identified in the Ilam dam section. 26 biozones and 2 sub-biozones have been identified based on the biological zoning of Wade et al., 2011 in the Tethys area. Based on the identified biozones, the age of Pabdeh Formation in the Ilam dam section, Middle Danian-Early Aquitanian has been obtained. The deposits of Pabdeh Formation in the section of Ilam dam have a thickness of 764 m (beginning of Pabdeh to the beginning of Kalhor anhydrite) which includes purple shale units (2 Units), marl limestone with lower limestone, cherti limestone, marl limestone with upper limestone. The lower boundary of Pabdeh Formation in this section is conform and continuous with shales and marls of Gurpi Formation but its upper boundary with the gypsums of the Asmari formation is most likely accompanied by a disconform.