رحیم کدخدائی ایلخچی

Identifying and locating stratigraphic traps is more difficult than structural traps because they are dependent on facies changes and their distribution follow the condition of the basin and the sedimentary environment. Accordingly, the three - dimensional seismic data based on seismic attributes provide a better way to establish lateral relationships with geological features. The purpose of this research is to identify the stratigraphic meandering channels by applying appropriate attributes on seismic data. For this purpose, three dimensional data from one of the northeastern fields of the Iran were employed by using Petrel software. Afterwards, the relevant attributes were applied on the raw sections and their reservoir characteristics were interpreted and surveyed. Through stratigraphic interpretations, the geometrical position of the meandering channels located in the Shurijeh Formation was better revealed by the envelope and extended spectral decomposition attributes. The spectral decomposition attribute was effective in revealing the geometry of meandering channels in seismic sections, and the envelope attribute confirmed the existence of meandering channels by showing bright spots related to stratigraphic oil traps. These results show good agreement with the results of lithological, facies, reservoir properties, and petrophysical interpretations of Shurijeh Formation in the study area.

The siliciclastic formations of Ojagheshlaq and Zeivar, as the reservoir rock of Moghan basin are of special importance. The sandstone facies of these formations are a unique example of unconventional reservoirs (tight sandstones) in Iran, which due to the textural and diagenetic characteristics affecting their pore system, have unstable production with pressure drop. In this study, the lithological and sedimentary characteristics of these formations were investigated by combining the results of core description, petrographic studies, scanning electron microscope images along with porosity and permeability data of the core obtained from outcrops and wells. The results show that the low mineralogical maturity of these sandstones, which mainly contain volcanic lithics and feldspar, has played an important role on modification and evolution of the pore system during their diagenetic history. In fact, the presence of volcanic lithics as compressible components is an effective factor in reducing the porosity of these sandstones during burial and compaction. Also, the alteration of these components along with feldspars has led to the formation of various diagenetic clays that have acted as cement inside the pores and have played an important role in developing micropores within the pore system. The dissolution process has also led to the development of isolated dissolution pores with limited expansion. In general, the interaction of three factors of compaction, diagenetic clays and dissolution in contrast to mineralogy, has played an effective role in the development of pore system and reservoir quality of Moghan basin sandstones, as a result of which tight sandstones with a compacted texture and pore system with a poor connection consisting of isolated dissolution pore types and micropores have been developed.

Various sources and methods used to identify different zones of a field that can investigate different zones and layers of the reservoir. The purpose of this study is to determine electrofacies and HFUs in the Kangan and upper Dalan Formations in one of the southern Iranian gas fields. The importance of determining and investigate the facies with the well quality and separation of this facies from other facies causes better knowledge of quality zones and also due to the use of available information can save time and money. In this study use well log, the concept of clustering and the MRGC method in Geolog software, the log petrophysical data were clustered and finally, 5 electrofacies were identified. Among these identified facies, electrofacies No. 4 with dolomite lithology was identified as the best reservoir zone due to high effective porosity and low shale volume. After determining electrofacies by using the aforementioned methods, HFUs were identified with core data. Finally, after determining the HFUs, to investigate the relationship between electrofacies and HFUs, the cross sections of wells and HFUs are placed next to the designated electrofacies. After examining depth to depth, a high correlation was observed between them. This result shows that, this electrofacies model can be used in all wells in this field.

In this study, the Qom Formation in Yortshah anticline has been evaluated as one of the reservoirs near Tehran city for gas storage. Formation of anhydrite is one of the diagenetic processes that can have a negative impact on reservoir properties. Petrographic investigation of c-4 to f members of the Qom Formation in Yortshahh anticline indicates the presence of 6 anhydrite textures including anhydrite layer, poikilotopic, pervasive and fracture filling cements and nodules and spare anhydrite crystals. Based on the results of petrophysical logs, anhydrite includes 3–8% of this reservoir. With the exception of anhydrite layer with the thickness up to 6 m in d member, which can be a potential cap rock for the lower reservoirs, anhydrite cements along with other cements have reduced the porosity of the reservoir. The porosity distribution in the members of the Qom Formation is affected by their different lithologies. As the e and f members due to different lithology than the c-4 member, in addition to the micropores, they also have fracture porosity, which increases the permeability and reservoir properties of these members.