persian gulf

Having knowledge about geological and engineering properties of marine sediments, is very important to perform stability analysis of offshore structures. In this paper, the geological engineering characteristics of marine sediments (from seabed to a maximum depth about 30 meters below seabed) was investigated in three oil and gas fields located in the northwestern Persian Gulf. In the first step, geotechnical database of study area was developed based on studies carried out by marine geotechnical labs and oil companies in Persian Gulf. Then, the distribution of physical and mechanical properties of marine sediments with depth and also their relation to the other parameters were studied and some graphs and geological/geotechnical profiles were drawn.The results showed that the physical and mechanical characteristics of these sites are influenced by the distance from the Iranian coast, water depth and distance from Arvand Rud river delta. Generally, from siteI to siteIII, the grains size, and liquid limit of fine-grained and strength of subseafloor sediments were increased. The thickness of soft sediments was decreased from siteI to siteIII. By evaluating the percent of carbonate content, it was found that with distance from the coast, the percent of carbonate content in subseafloor sediments were decreased. So, the least amount of carbonate content was observed in site III. According to the result of PI versus PL/LL graph, Illite is the most abundant clay mineral in the study area.

Comprehensive geochemical study shows the genetic relationship between 14 samples of gas condensates from the Persian Gulf. In this study, the samples were examined merely in terms of maturity, which led to a general trend towards maturation of the region. In this process, maturation increases from west to east of the Persian Gulf and also from the coastal Fars to the Persian Gulf and then to the Arabian section.
 

By using data collected including data biomarkers derived from gas chromatography-mass spectrometry analysis to provide relevant diagrams for maturity and source rock sedimentation environment, as well as statistical analysis of existing samples for all fields, which ultimately, by matching the interpretations of these two to the desired results, the purpose of this Research has been achieved.

The Samples were collected from Dalan and Kangan reservoirs (Late Permian – Triassic) from 6 gas fields (gas condensate), Which constitute the most important Iranian gas/gas condensate reservoirs. In this  study, in order to estimate the maturity of samples (for the purpose of determining the thermal maturity of gas condensates and determining their range of placement in the maturity chart), as well as determining the sedimentary environment of the source rock and type of lithology, the available biomarker parameters obtained from the results gas chromatography - mass spectrometry (GC-MS) were used. The statistical methods used are agglomerative hierarchical clustering (AHC) and principal component analysis (PCA), which show that the studied gases are in three main genetic groups.

According to the results of this study, the origin of hydrocarbons in the region of marine organic matter with some organic matter of continental origin, which maturity range is in the late stages of petroleum production and early gas window. This gas condensate is derived from the clastic lithological sources that have been generated under reducing environmental conditions and from type II and III kerogens. The three main groups of gas condensate from statistical analysis and make correlation to the source rock were identified using biomarker parameters related to maturity and sedimentation environment. The maturity from the Golshan field to the Salman field (from west to east of the Persian Gulf) increases and the sedimentary environment is different in the southern Persian Gulf Salman and Golshan fields (marine carbonate) from its northern fields such as Khayyam, Tabnak and Madar (marine shale).

Hierarchical cluster and principal component analysis are two statistical methods frequently used by geochemists to study the group of variables. In order to identify oil families in the Iranian sector of Persian Gulf, 33 oil samples were collected and analyzed by advanced gas chromatography, gas chromatography-mass spectrometry and Finnigan Delta Plus mass spectrometer. On the whole, 16 parameters were considered as the input data for Hierarchical cluster and principal component analysis. Four different oil families at least could be identified through the Iranian sector of Persian Gulf based on the results obtained. These families were categorized stratigraphically and regionally. Accordingly, oil families No. I and No. II in west and east of Persian Gulf respectively, are located in the Jurassic to early Cretaceous reservoirs, whereas oil families No. III and No. IV in west and east of Persian Gulf belong to Late Cretaceous to Tertiary reservoirs.

This paper summarizes geochemical analysis and burial and thermal history modeling of Dorood and Nowrooz oil fields located in northwestern Persian Gulf. 5 samples of Fahliyan (Yammama), Asmari and Fahlian (Manifa) reservoirs in Dorood - Kharg oil field and Kazhdumi (Nahreomr) and Kazhdumi (Burghan) reservoirs in Nowrooz oil field were analyzed geochemically. Samples are mainly paraffinic oil type. Oil in Dorood - Kharg reservoirs were originated from carbonate sulfur rich source rock but marl or calcareous shale rock is responsible for oil generation in the Nowrooz field. Isotopic studies indicate that Kazhdumi (Nahreomr) reservoir is likely contain composite oil. Based on the results of burial and thermal history modeling of Dorood and Nowrooz oil fields, the Surmeh (Arab - D) formation began to generate oil from about 125 million years ago and lies in main oil window and Kazhdumi (Dair) formation is thermally immature in Nowrooz oil field. Kazhdumi and Gadvan formations lie in early oil zone and Pabdeh formation is immature in Dorood oil field.