نشریه زمین شناسی نفت ایران
سال دوم شماره 2 (پیاپی 4، پاییز و زمستان 1391)

Pabdeh Formation is one of the most important probable source rocks in Mansuri oilfield being under investigation. In this study, hydrocarbon potential of Pabdeh Formation is evaluated. Also effect of sedimentary environment changes on geochemical and hydrocarbon potential variation is studied. To achieve this, hydrocarbon potential of Pabdeh Formation with Rock Eval pyrolysis was investigated. Besides that, gas chromatography and gas chromatography- mass spectrometry data were utilized. Based on this study, in the Late Eocene age, relative sea level had raised, while in the Oligocene age, falling in sea level was occurred. Variation in sea level caused Pabdeh Formation to be heterogeneous in hydrocarbon potential. Pabdeh Formation in Mansuri oilfield from geochemical aspects is divided into three divisions. Lower and Upper zones in this formation, have fair (0.5-1% TOC) to good (1-2% TOC) hydrocarbon potential and contain kerogen type III. These zones have gas production potential. Middle zone, has very good (2-4% TOC) to excellent (>4% TOC) potential and contains kerogen type II and mixed type II and III. Middle zone has oil production potential. Rock Eval data as well as thermal history modeling demonstrate that; Pabdeh Formation is in early oil window, started yielding petroleum since 5-6 million years ago.

The Asmari Formation in the Marun oilfield is composed of fossiliferous limestone, dolomitic limestone, argillaceous limestone, sandstone and shale. It is the major reservoir rock of Iran in several oil fields of the Zagros Basin. The age of Asmari Formation in this oilfield is Oligo-Miocene (Rupelian–Burdigalian). In this study, subsurface correlation between the four wells in the Marun oilfield, based on climate stratigraphy is done by using Cyclolog Software. Nine Positive and ten negative bounding surfaces have been identified. Some positive and negative bounding surfaces coincide with sequence boundaries and maximum flooding surface, respectively. In addition, some of the positive bounding surfaces identified the main time boundary (stage boundaries). Reservoir correlation between the ten compartments reservoir zones of the Asmari Formation in the Marun oilfield is done with these boundary surfaces. Some reservoir zones (especially the lower and middle Asmari reservoir zones) show perfect matching but others do not show the boundary of adaptive zones. It seems combining these data with other factors such as lithology, porosity and permeability, detail revision of reservoir zoning of Asmari Formation in Marun Oilfield is required.

In this research, biostratigraphy, microfacies and paleoenvironment of the Asmari Formation in the Fars province (Tang-e Abolhayat, Naura anticline, south-west of Firozabad, Khormuj anticline), High Zagros (Shoorom anticline), Izeh zone (Mokhtar anticline), Dezful Embayment (Tang-e Anbar Sepid, Dill anticline, Khaviz anticline, Aghajari oil field) and Lurestan province (Mamulan, Sepid-Dasht, Dehluran and Kabirkuh-Darreshahr), were reviewed and revised for the comprehensive understanding of age and depositional environments.The Globigerina spp.-Turborotalia cerroazulensis-Hantkenina and Nummulites vascus-Nummulites fichteli assemblage zones (Rupelian) are present in Fars province. The dominated microfacies within the Asmari Formation of the Rupelian time are bioclast planktonic, nummulitidae lepidocyclinidae wackestone-packstone, of an outer and middle ramp depositional setting.The Archaias asmaricus-Archaias hensoni-Miogypsinoides complanatus assemblage zone (Chattian) is present in Fars, High Zagros, Izeh and Dezful Embayment provinces. The dominated microfacies within the Asmari Formation of the Chattian time are bioclast perforate-imperforate foraminifera wackestone-packstone and mudstone, of an inner ramp depositional setting.The Miogypsina-Elphidium sp. 14-Peneroplis farsensis assemblage zone (Aquitanian) is present in High Zagros, Izeh, Dezful Embayment and parts of the Fars and Lurestan provinces. The dominated microfacies within the Asmari Formation of the Aquitanian time are perforate-imperforate foraminifera bioclast wackestone-packstone, grainstone and mudstone, of an inner ramp depositional setting.The Borelis melo curdica-Borelis melo melo assemblage zone (Burdigalian) is present in most areas. But it slightly occurs in Fars province. The microfacies of the Asmari Formation during Burdigalian are similar to those of Aquitanian. In Sepid-Dasht and Tang-e Anbar Sepid sections due to presence Globigerina spp. assemblage zone and planktonic foraminifera wackestone-packstone facies, an outer ramp depositional setting is also suggested.

The Upper Dalan and Lower Kangan stratigraphic units with 225m thickness were studied in one of the subsurface section in Persian Gulf area. According to the biostrarigraphic investigation on the dolomitic and limestone successions of the Upper Dalan unit, there are more than 30 index foraminifera and non-foraminifera species. One Paradagmarita/ Paraglobivalvulina/ Baisalina Assemblage Zone that divided to three distinct sub- assemblage zones1. Rectostipulina quadrata/ Globivalvulina vonderschimitti Assemblage subzone2. Dagmarita chanackchiensis/ Ichtyolaria latilimbata Assemblage subzone3. Hemigordiopsis renzi/ Paradagmarita flabeliformis Assemblage subzonehave been distinguished in the stratigraphic section representing the Julfian to Earleast Dorashamian stage. The identified microfauna' assemblages can be corresponded to the Late Permian regional biozonation in the Tethys realm. The latest microfauna assemblages in the latest part of Dalan Formation exhibits a significant chronostratigraphic hiatus, just was cited in the Dalan/ Kangan (Permo/Triassic) boundary. There is no any evidence about Latest Dorashamian sediments in the study area. The Permo/Triassic boundary is a paraconformity type in the latest Permian biozones, which can be corresponded to other areas of the world. The Lower Kangan stratigraphic unit can be attributed to the Schytian age (Early Triassic age) on basis of presence of some index fossils such as Bivalves (Claraia sp.) and Serpulids (Spirorbis sp.). It should be stressed that the similar microfauna associations can be seen in other Iranian places such as Central Iran and Alborz areas, which is documented a distinct palaeobiogeographical relationship between the above-mentioned areas and Zagros realm on Permian and Triassic ages.

Exact assessment of reservoir fluid contacts and distribution is an important part of reservoir characterization. Reservoir fluid contacts may be detected by petrophysical interpretations, well testing, special core analysis and seismic inverse modeling techniques. In practice, due to non-economic and unavailability of well test and seismic data, wire line log data are commonly used. Since these contacts affected by complexity of reservoir properties, thickness of reservoir rocks, and some factors such as vug effect, fractures and mud filtrate invasion, it is essential to find a way for reducing such these factors. The present study uses data related to three wells of an oil field in southwestern Iran to detect oil-water contact by continues wavelet transform of resistivity log. The results obtained from this method are compared with well test responses to validate the proposed algorithm. The results show that this method is capable to detect fluids contact accurately.

Permeability is one of the main parameters in the study of hydrocarbon reservoirs which are needed to be measured correctly. The conventional methods are well testing and direct permeability measurement on the drilled core samples. Absolute air permeability of core plug samples is often measured in the laboratory which is cheap and fast.The absolute air permeability of a rock sample depends on the flowing mean pressure and type of gas and varies with changing them. Hence, measuring liquid permeability of fully saturated core sample or determination of corrected gas permeability which is equivalent to the liquid permeability is essential. This needs to spend enough time and budget. Klinkenberg investigated the effect of gas slippage in porous media and measured absolute permeability of different gases in various mean pressures. He yielded an equation for correcting absolute gas permeability and defining equivalent liquid permeability.The aim of this study was to present some practical relations for determining Klinkenberg corrected gas permeability of carbonate rocks by using their absolute air permeability, which has not been reported yet. For this purpose, Klinkenberg corrected gas permeability of 541 core plugs, with various petrophysical properties from different carbonate formations in the Southwest of Iran was measured. Exponential relations were obtained with very good correlation coefficients. Considering vast petrophysical properties of the studied samples, the yielded equations can be used to predict and determine equivalent liquid permeability of carbonate core samples of Southwest of Iran from their absolute air permeability.

In this study 44 Sedimentary rock samples from the Amadeus Basin, in southern portion of the Northern Territory, Australia, were analyzed by two well-proven organic geochemical Rock-Eval (RE) pyrolysis and gas chromatography–mass spectrometry (GC–MS) analysis. These techniques were used to obtain independent parameters on organic matter composition, its thermal maturity, and environment of deposition. This study reveals a close concordance between Rock-Eval pyrolysis data and polycyclic biomarkers parameters such as steranes.RE pyrolysis in conjunction with GC–MS analysis show that the Amadeus Basin sediments contain a variable but notable organic-rich facies in the Horn Valley siltstone and prove an unequivocal evidence for Type-II organic matter, which lies dominantly to the peak stage of the conventional oil window (end of diagenesis-middle of catagenesis). The case study from the Amadeus Basin shows that these methods remain undoubtedly suitable for a good assessment of the petroleum potential of source rocks and rapid geochemical characterization of sedimentary organic matter, and can be used in other similar basins.