Gulf Basin Research Articles

Ecological niche overlap from occurrence of two cyprinid sympatric species, Paracapoeta trutta and Capoeta damascina in the Sirvan River, Persian Gulf Basin

Ecological niche overlap from occurrence of two cyprinid sympatric species, Paracapoeta trutta and Capoeta damascina in the Sirvan River, Persian Gulf Basin

Response of Shallow-Water Temperature and Significant Wave Height to Sequential Tropical Cyclones in the Northeast Beibu Gulf

Using shallow-water buoy observations, reanalysis data, and numerical models, this study analyzes the variations in sea temperature and significant wave height (SWH) caused by two sequential tropical cyclones (TCs) ‘Lionrock’ and ‘Kompasu’ in October 2021 in the northeast Beibu Gulf, South China Sea. The results show that the sea surface temperature (SST) cooling of the nearshore waters was larger than the offshore water in the basin of the gulf, with the cooling amplitude and rate decreasing and the cooling time lagging behind wind increasing from coast to offshore. The near-surface temperature at the buoy station had a maximum decrease of 2.8 °C after ‘Lionrock’, and the decrease increased slightly to 3 °C after the stronger wind of ‘Kompasu’. The total decrease of 4.6 °C indicates that the sequential TCs had a superimposed effect on the cooling of the Beibu Gulf. The heat budget analysis revealed that the sea surface heat loss and the Ekman pumping rate in the nearshore waters during ‘Kompasu’ (−535 W/m2 and 5.8 × 10−4 m/s, respectively) were significantly higher than that (−418 W/m2 and 4 × 10−4 m/s) during ‘Lionrock’. On the other hand, the SST cooling (−1.2 °C) during the second TC is smaller than (−1.6 °C) the first weaker TC in the gulf basin, probably due to the deepening of the mixed layer. During the observation period, the waves in the Beibu Gulf were predominantly wind-driven. The maximum SWHs reached 1.58 m and 2.3 m at the bouy station near shore during the two TCs, and the SWH variation was highly correlated to the wind variation with a correlation of 0.95. The SWH increases from the nearshore to offshore waters during the TCs. The SAWN and ARCIRC coupled model results suggest that wave variations in the Beibu Gulf are primarily influenced by water depth, bottom friction, and whitecapping. Two days after the TCs, sea surface cooling and high waves appeared again due to a cold air event.

Microfacies, diagenetic processes and reservoir quality of the Aptian carbonate Dariyan Formation, southeast of the Persian Gulf, South Iran

The Aptian carbonate Dariyan Formation (Shu'aiba equivalent) is one of the most important oil reservoirs in the Zagros Basin and the Persian Gulf (South and Southwest of Iran). The Dariyan Formation with mainly carbonate facies overlies the Gadvan (Hawar) Formation and is overlain by the Kazhdumi (Nahr Umr) Formation. Despite the reservoir importance of the Dariyan Formation, it seems that not much detailed work has been done about the facies characteristics, diagenetic processes and reservoir quality of this formation in the east of the Persian Gulf Basin of Iran.By using the new and valuable data obtained from the core, this study focused on the identification of microfacies, diagenetic processes, determining the sedimentary environment, biostratigraphy and reservoir characterization of this formation in one of the wells of Reshadat oilfield in the southeast of the Persian Gulf. The results obtained from microfacies study, led to the identification of seven carbonate and one mixed carbonate-clastic microfacies that were deposited in four facies belts including the inner ramp, middle ramp, outer ramp, and deep basin. Uniform facies changes and the absence of reef-forming organisms such as rudists and its replacement by Lithocodium algae with the ability to form patch reefs indicate the homoclinal carbonate ramp environment. The study of benthic and planktonic foraminifera, as well as algae, led to the identification of five biozones, which indicated the Aptian age for this formation.Based on petrographic study, the Dariyan Formation is affected by diagenetic processes such as Cementation, dissolution, mechanical and chemical compaction, dolomitization, bioturbation and pyritization. Correspondence of porosity and permeability data of the cores and petrophysical logs indicates that the reservoir quality of the Dariyan Formation in the studied field was affected by facies, and diagenesis factors. Reservoir characterization has revealed that the high quality zone is located in the intervals containing Lithocodium algae. In the Lithocodium-bearing facies (boundstone-floatstone) the presence of many interconnected pores and cavities in the skeletal network structure of Lithocodium/Bacinella algae have created a suitable reservoir quality and a permeable facies.

Intelligent Identification and Quantitative Characterization of Pores in Shale SEM Images Based on Pore-Net Deep-Learning Network Model

Among the various shale reservoir evaluation methods, the scanning electron microscope (SEM) image method is widely used. Its image can intuitively reflect the development stage of a shale reservoir and is often used for the qualitative characterization of shale pores. However, manual image processing is inefficient and cannot quantitatively characterize pores. The semantic segmentation method of deep learning greatly improves the efficiency of image analysis and can calculate the face rate of shale SEM images to achieve quantitative characterization. In this paper, the high-maturity shale of the Longmaxi Formation in the Changning area of Yibin City, Sichuan Province, and the low-maturity shale of Beibu Gulf Basin in China are studied. Based on the Pore-net network model, the intelligent identification and quantitative characterization of pores in shale SEM images are realized. The pore-net model is improved from the U-net deep-learning network model, which improves the ability of the network model to identify pores. The results show that the pore-net model performs better than the U-net model, FCN model, DeepLab V3 + model, and traditional binarization method. The problem of low accuracy of the traditional pore identification method is solved. The porosity of SEM images of high-maturity shale calculated by the pore-net network model is between 12 and 19% deviation from the experimental data. The calculated porosity of the SEM image of the low-maturity shale has a large deviation from the experimental data, which is between 14 and 47%. Compared with the porosity results calculated by other methods, the results calculated by pore-net are closer to the true value, which proves that the porosity calculated by the pore-net network model is reliable. The deep-learning semantic image segmentation method is suitable for pore recognition of shale SEM images. The fully convolutional neural network model is used to train the manually labeled shale SEM images, which can realize the intelligent recognition and quantitative characterization of the pores in the shale SEM images. It provides a certain reference value for the evaluation of shale oil and gas reservoirs and the study of other porous materials.

Redescription of Cyprinion muscatense (Teleostei: Cyprinidae) with the first phylogenetic analysis of the genus.

Members of the genus Cyprinion (Cypriniformes: Cyprinidae) are found in the Indus River basin west to the Arabian Peninsula and the Tigris-Euphrates River drainages (Persian Gulf basin). The taxonomic status of Cyprinion including Cyprinion muscatense is poorly understood when compared to other cyprinid genera. C. muscatense has been considered as a member of the Cyprinion watsoni-microphthalmum group and a valid species endemic to the Arabian Peninsula. Here, we redescribe C. muscatense based on an integrative morphological and molecular approach and freshly sampled material from several localities in the Oman Mountains ecoregion. The results showed that C. muscatense is distinguished from the other Cyprinion species in the Arabian Peninsula by having a short, thin, and slightly serrated last unbranched dorsal fin ray; the lower number of circumpeduncular scales; lateral line scales; and also scales between the lateral line and the dorsal-fin origin. Subterminal mouth, presence of one pair of small barbels at the mouth corner, 3-4 unbranched and 9½-10½ dorsal-fin branched rays, 12-14 pectoral-fin rays, 7-8 pelvic-fin rays, 2-3 unbranched and 6½-7½ branched anal-fin rays, and 37-40 lateral line scales are other morphological characteristics of C. muscatense. C. muscatense is also well distinguished by molecular characters among its congeners. The first molecular phylogenetic analysis of the genus, covering all currently recognized Cyprinion species except for C. watsoni, is also presented. C. muscatense is resolved as the sister species to another endemic fish of the Arabian Peninsula Cyprinion mhalense, with a Kimura-2-Parameter model distance of 5.3%.

Integration of well logs and seismic attributes for prediction of thermal maturity and TOC content in the Kazhdumi Formation (central Persian Gulf basin)

This study proposes an indirect method for estimating source rock properties, specifically thermal maturity and Total Organic Carbon (TOC), using well logs and seismic data within the central Persian Gulf hydrocarbon fields. The primary focus is on the Kazhdumi Formation, an important source rock in the southern Iran. The study is carried out in two distinct steps, based on the employed data. In the first step, a Maturity Index (MI) is calculated utilizing well logs (such as neutron, density and water saturation) within the Kazhdumi Formation across six oil and gas fields. Then, the TOC content is determined using ∆Log R method across four wells. Geochemical data, including vitrinite reflectance and Rock-Eval pyrolysis data, used as validators of the calculated MI and TOC. In the second step, 2-dimensional post-stack seismic data analysis is conducted where the necessary data, including a full set of well logs are accessible. Multi-attribute regression is employed to extract seismic attributes and consequently used to predict the target parameters. MI and TOC logs are then predicted through Probabilistic Neural Network analysis (PNN) which is used for the indirect prediction of the target logs. Finally, two seismic volumes are obtained to provide a mapping of the predicted MI and TOC variations in the Kazhdumi Formation.One advantage of using this method is its efficiency and cost effective compared to the geochemical testing. Additionally, it provides a continuous prediction of the target parameter in an extensive area. Lastly, this method benefits from the availability of seismic data compared to the geochemical data in hydrocarbon fields that are typically sparse. This approach is proved to be applicable to source rock analysis in different areas for indirect estimation of thermal maturity and TOC.

Integration of geochemical data, well logs and seismic sections for source rock characterization of the Albian Kazhdumi Formation in the central Persian Gulf basin, South Iran

This study presents indirect methods of source rocks characterization by integrating geochemical data with well logs and seismic inversion results. Well logs and seismic data are commonly more available than scarce geochemical data in oil and gas fields. Combining high vertical resolution well logs with high lateral resolution seismic data generates some enhanced geochemical data on inter-well spaces where no well is drilled.Acoustic impedance was obtained and utilized for the TOC prediction and source rock detection because of its good correlation with geological parameters such as the lithology and fluid contents. A cross-plot of log-derived water saturation versus acoustic impedance successfully differentiates source from non-source rocks based on geological variations of lithology, porosity, formations density, and the TOC content. The impact of the TOC content on acoustic properties was elaborated in the next step. Acoustic impedance is obtained as the most important seismic attribute for the TOC prediction. Well logs and seismic data are integrated to predict the TOC logs from seismic data. First, seismic data were inverted to obtain the acoustic impedance. Then, the produced acoustic impedance was used as a seismic attribute for the TOC prediction. The outcome is used to illustrate and follow the TOC variation to distinguish source rocks in the oil and gas fields. The study is carried out in the Cretaceous succession in three hydrocarbon fields in the central part of the Persian Gulf to observe the TOC variations in the Albian-aged Kazhdumi Formation.

Prototypes, modifications, and hydrocarbon enrichment variations in basins influenced by Tethyan evolution: A comparative analysis of the Persian Gulf Basin and the Sichuan Basin

Prototypes, modifications, and hydrocarbon enrichment variations in basins influenced by Tethyan evolution: A comparative analysis of the Persian Gulf Basin and the Sichuan Basin

Microbial Community Composition as an Indicator of the State of Basins Located at the Sea Coast (Exemplified by the Kanda Bay, Kandalaksha Gulf, White Sea)

Abstract—Formation of the Kanda Bay resulted from construction of a railway dam (1916) and subsequent isolation of the sea lagoon from the main basin of the Kandalaksha Gulf, White Sea. Decreased action of tidal flows, which mix the water column of the lagoon, altered the hydrological regime of the basin. Decreased water exchange resulted in formation of oxygen-depleted near-bottom water and to sulfide contamination. A freshwater lake was, however, preserved in the southern part of the Kanda Bay. The composition of microbial communities was studied for the near-bottom water horizons at different sides of the Kanda Bay. The oxygen regime in this layer was found to change, with increasing concentrations of sulfide and methane and active processes of sulfate reduction and methane oxidation. The composition of the microbial community changed noticeably, with lower abundance of true marine and freshwater microorganisms and development of bacteria and archaea predominant in microbial communities of anoxic water in meromictic basins. Among the microbial diversity, indicator species with increased abundance were revealed. These are archaea of the genera Methanoregula and Methanosaeta (phylum Halobacterota). The sulfur cycle microorganisms, which were the indicators of stagnant marine water, included anoxygenic phototrophic bacteria of the class Chlorobia, (Chlorobium phaeovibrioides, Pelodictyon phaeoclathratiforme), Chloroflexi of the genus Chloronema, nonsulfur purple bacteria related to the genus Rhodoferax, colorless sulfur bacteria of the family Beggiatoaceae, and sulfur oxidizers of the genus Thiobacillus. Archaea of the genus Nitrosopumilus (phylum Crenarchaeota) and bacteria of the genus Woeseia may be considered opposites to the indicator microorganisms, since they were found only in the open sea water. In our opinion, stable water exchange through the dam will result in the stable composition of the Kanda Bay microbial community, with only seasonal variations and year-to-year fluctuations. The negative scenario supports prediction of conversion of the Kanda Bay into a stratified basin with anoxic near-bottom water and the microbial community similar to that found in meromictic lakes.

Progress in research on the exploration and evaluation of deep geothermal resources in the Fujian-Guangdong-Hainan region, China

Deep geothermal resources in the Fujian-Guangdong-Hainan region, China, offer significant potential for sustainable energy. The diverse igneous rock formations along the southeast coast present intricate geological challenges that impede exploration and evaluation efforts. In this study, we address critical concerns related to the Fujian-Guangdong-Hainan region's deep geothermal resources, encompassing heat source composition, formation conditions, strategic favorable areas, and exploration directions. Our methods involve the analysis of regional geothermal reservoirs and cap rocks. Major findings include: the primary heat sources in the Fujian-Guangdong-Hainan region consist of the radioactive heat generation from granites in the crust, heat conduction in the mantle, and, in specific areas like Yangjiang and Shantou, melts within the middle and lower crust; the deep, high-temperature geothermal resources in the region predominantly reside in basins' depressed areas. These areas are characterized by the confluence of triple heat sources: heat from the Earth's crust, mantle, and other supplementary sources; our analysis led to the identification of three strategic areas favorable for deep geothermal resources in the Fujian-Guangdong-Hainan region. These are the Beibu Gulf Basin's continental area, the Yuezhong Depression, and the Fuzhou-Zhangzhou area.

The Clay Mineralogy and Geochemistry of Sediments in the Beibu Gulf, South China Sea: A Record of the Holocene Sedimentary Environmental Change

In this study, we analyzed the clay mineralogy and geochemistry of surface and drill core samples from the northeastern Beibu Gulf in order to unravel the sediment provenance of, and factors controlling, the sedimentary environment. The main clay mineral assemblage in the surface sediment samples included kaolinite (27–72%), smectite (4–51%), illite (7–20%), and chlorite (8–17%). The study area comprises three major clay distribution zones (from the northeastern coastal area to central Beibu Gulf basin), i.e., the kaolinite-dominated, kaolinite–smectite, and smectite-dominated zones. The zoning of the clay mineralogy and major and trace elements indicated the mixing of coarse terrigenous sediments with distal fine sediments. Early Holocene sea level rise was documented in core B15-1, which had three sedimentary units (divided into Units 1–3 from top to bottom), as revealed by the changes in the dominant clay minerals and geochemical/oxide ratios (SiO2/Al2O3, Rb/Sr, Sr/Ba, and Ti/Ca) in Unit 2. Unit 1 and Unit 3 were likely deposited in the continental and marine environments, respectively. The low sedimentation rate and hydrodynamic disturbance may have influenced the deposition process more than climatic fluctuations.

Spatiotemporal distribution and mechanism of Mesozoic magmatism in the South China Sea and its adjacent areas: insights from seismic, geochemical, and geochronological data

ABSTRACT Mesozoic igneous rocks are widely distributed in the South China Sea (SCS) and its adjacent areas and are exposed in the SCS, South China, Hainan, Indochina, Taiwan, the Philippines, and Borneo; these rocks are mostly dominated by granitoids. This paper presents a complete map of the Mesozoic igneous rocks of the SCS and its adjacent areas. This paper also presents an analysis of geological survey and published data in terms of seismic profiles, ages, geochemistry and isotopic systematics of the Mesozoic igneous complexes of the SCS and its adjacent areas. Three periods of igneous activity can be distinguished: (1) Permian – Triassic that spans from 250–201 Ma; (2) Jurassic (201–145 Ma); and (3) Latest Jurassic/Cretaceous to Maastrichtian (145–66 Ma), of which the Cretaceous is the best preserved and could possibly be the most widespread. Triassic igneous rocks are distributed in the northwestern and southern SCS (Qiongdongnan Basin, Yinggehai-Song Hong Basin, Beibu Gulf Basin, the Dangerous Grounds, and the Reed Bank); Jurassic igneous rocks are distributed in the northern and southern SCS (Pearl River Mouth Basin, Qiongdongnan Basin, Yinggehai-Song Hong Basin, Beibu Gulf Basin, and the Reed Bank); and Cretaceous igneous rocks are distributed in the northern, western and southern SCS. The igneous activity of the SCS is mostly distributed in the continent slope. Mesozoic igneous rocks of the SCS include at least 350 rock masses: the smallest being 0.182 km2, the largest being 5,5,502 km2, and the total area covering 688,539 km2. Mesozoic magmatism in the SCS and its adjacent areas migrated oceanward (southeastward). Our new seismic profiles and the wells from the literature highlight that Jurassic granites occur not only inland of South China but also in coastal South China and the northern and southern SCS. The YING6 well in the northern SCS encountered andesite with an age of 68.24 Ma, which is the youngest age found for the SCS Mesozoic volcanic rocks. The XY1 well in the western SCS encountered granite with an age of 68.9 Ma, which is the youngest age found for the SCS Mesozoic intrusive rocks. The WZ12-3-1 well in the northern SCS encountered granite with an age of 243.3 Ma, which is the oldest age found for the SCS Mesozoic intrusive rocks. The encountered dacite ages (219.1 ± 1.4 Ma) of the NK-1 well in the southern SCS were the oldest ages found for the SCS Mesozoic volcanic rocks. The thickest Mesozoic igneous rocks (>1022.5 m) were encountered in the NK-1 well. Igneous rocks in the SCS and its adjacent areas are closely related to tectonic movements such as faults, plate movement, and mantle-derived igneous fluid ascent. They are controlled by the subduction of the Tethys lithospheric and Paleo-Pacific domains.

Glyptothorax vatandousti, a new species of torrent catfish from the upper Karkheh drainage in Iran (Teleostei: Sisoridae).

Glyptothorax vatandousti, new species, from the upper Karkheh drainage, a tributary of the Iranian Tigris, is distinguished from its congeners in the Persian Gulf basin by having the flank with a fine, pale-brown mottled pattern overlaid by small and large, blackish or dark-brown blotches, deep caudal-peduncle (its depth 1.1-1.3 times in length), and without, or with a pale-brown triangle-shaped blotch in front of dorsal-fin origin.

Geochemical characteristics and oil–oil correlation of the upper Cretaceous oils from the Iranian part of the Persian Gulf Basin

The Cenomanian Sarvak oil reservoirs are distributed over large areas of the Persian Gulf basin. The purpose of this study is analyzing the geochemical characteristics of the Sarvak oil reservoirs and their inter-relationships in the Persian Gulf, classification of the Sarvak oil samples and investigation of the possible causes of the genetic difference in oil families. In the previous studies, limited samples of Sarvak oil reservoir in scarce oilfields were studied individually and local interpretations are made accordingly. The current study employs a more complete set of geochemical from the Iranian part of Persian Gulf and regional interpretations are drawn. To achieve this goal, the geochemical data of 41 oil samples from 10 oilfields were collected and assessed based on gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS), and stable carbon isotope analysis. It was demonstrated with the evaluations that the oils accumulated in the Upper Cretaceous Sarvak reservoirs in the Persian Gulf basin originate from different source rocks. The oil samples are genetically classified into four oil families based on the similarities and differences of parameters related to the depositional environment-dependent parameters using hierarchical cluster analysis (HCA), star diagram, and stable carbon isotope diagram. The source rocks were mainly deposited in anoxic marine carbonate environments. The thermal maturity of the oils was evaluated using steranes and trisnorhopanes. Oil families 2 and 4 (located at the center of the Persian Gulf) have the highest thermal maturity compared to the other samples; in contrast, oil family 1 (located at the west of the Persian Gulf) has the lowest thermal maturity. The possible source rocks of oil family 1 and family 3 (located at eastern Persian Gulf) using C28/C29 steranes are the upper Cretaceous successions; in contrast, the possible source rocks of oil families 2 and 4 are the upper Triassic and Lower Jurassic formations. Results of the study show a high similarity between the oils of families 2 and 4, which are located at the center of the Persian Gulf; these results also recognize the significant difference between these two oil families and oil families 1 and 3. The significant issue raised in this study is to find out the reason for this difference. The structural analysis of the central Persian Gulf shows that huge vertical faults created by salt domes intrusion provided the migration pathways for trapping oil in Sarvak reservoirs. The oils of the Surmeh, Fahliyan, and Dariyan reservoirs have migrated upwards through these faults to be trapped in the Sarvak Formation across the central Persian Gulf.

Mystus misrai Anuradha, 1986, a valid species from the Orontes drainage (Teleostei: Bagridae).

Mystus misrai from the northern Orontes drainage (Mediterranean Sea basin) is re-examined and recognised as a valid species. It is distinguished from M. pelusius from the Gulf basin by the lack of stripes on the flank, shorter fins, the eye situated below the dorsal head profile, and a K2P distance of 7.3% in its COI barcoding gene. Mystus misrai is likely Critically Endangered: only a single, spring-fed lake in Türkiye is known as its habitat. The biogeographic connection between the Orontes and the Gulf is discussed based on molecular data of 27 species native to the region.

Microbial Communities Associated with the White Sea Red Algae as a Source of Xylanolytic Microorganisms

Abstract—Microorganisms associated with algae and able to utilize complex substrates (e.g., plant heteropolysaccharides) may be important producers of hydrolytic enzymes. The microbial communities of the red algae Corallina sp. and Phyllophora sp. sampled in the Kandalaksha Gulf basin of the White Sea were analyzed using high-throughput sequencing of the V4-variable region of the 16S rRNA gene. The dominant phyla in microbiomes of both samples were Pseudomonadota and Bacteroidota (GTDB classification, https://gtdb.ecogenomic.org/). For the Corallina sp. sample, dominance of the Vibrio, Agarivorans, and Photobacterium genera was shown, while Granulosicoccus and Aliivibrio dominated in the Phyllophora sp. sample. The analyzed red macroalgae with associated microbiota were used as an inocula to obtain microbial enrichment cultures growing on β-1,4-xylan or β-1,3-glucan (сurdlan). It was shown that, similar to environmental samples Pseudomonadota and Bacteroidota phyla representatives were prevalent in all enrichment cultures. However, unlike the environmental samples, in the enrichment cultures the dominant genera were Marinomonas, Reinekea, Polaribacter, and Pseudoalteromonas. The latter, as well as the representatives of Vibrio sp., were isolated in pure cultures for which the xylanolytic activity was shown.

3D basin and petroleum system modelling of the early cretaceous play in the NW Persian Gulf

Petroleum systems analysis has become a key part of hydrocarbon resource exploration. Early Cretaceous petroleum system in the northwest of the Persian Gulf basin with prolific source rocks and reservoirs, is the main petroleum system in the region. Most Iranian offshore oils have been stored in this geological interval. Recent studies indicate that finding new resources is still possible. Therefore, for the first time, this study applied a 3D petroleum system modeling approach to predict new prospects based on available seismic and well data in ∼30,000 km2 area. Results showed that the Berriasian Garau, Albian Kazhdumi and Barremian upper Gadvan are the dominant source rocks. Most of the hydrocarbons have originated from the two Binak and Northern troughs as oil kitchens in the northern and northwest areas. Most anticlines formed in the Late Cretaceous before the critical moment of the source rocks. At first, traps adjacent to the Binak and Northern troughs oil kitchens were charged. Then, hydrocarbon migrated laterally to the far structures. The activity of normal faults has played an important role in vertical migration and reservoir oil mixing, especially in oilfields located above the Khafji-Norooz Arch. Albian Burgan sandstone distribution map from process-based forward stratigraphic modeling suggests low probability of stratigraphic traps. Nonetheless, the Burgan anticline reservoirs have the highest oil in place because they have broad drainage area. Finally, three new anticlinal traps with significant oil reserves were identified in the Yamama, Burgan, and Khalij formations in the northwest of the study area. Results of this study help to better understand Early Cretaceous petroleum system performance and identify new hydrocarbon prospects in the study area.

Geochemical assessment of upper Cretaceous crude oils from the Iranian part of the Persian Gulf Basin: Implications for thermal maturity, potential source rocks, and depositional setting

The Upper Cretaceous carbonate successions of the Sarvak Formation host giant oil reservoirs in the Persian Gulf. In this research, a total of 28 oil samples from nine oilfields located in the western, central and eastern parts of the Persian Gulf region were studied to determine the genetic relationships of oils, depositional setting of possible source rocks, thermal maturity, and source-rock ages in the Persian Gulf basin. According to the measured geochemical data, the source rocks facies vary from marine carbonates and marl/carbonates in the central and eastern oilfields to shale/carbonates in the western oilfields. The Pr/Ph ratio, steranes and terpanes suggest anoxic to dysoxic conditions of the depositional environments. The depositional environments experienced both low water stratification/low salinity and normal salinity/unstratified conditions. Evaluation of the saturated and aromatic biomarkers shows that all oil samples are mature and most of the source rocks lie within the beginning of the oil-generation window. The thermal maturity of the central oilfields is higher than that of the other samples, and has gone beyond the oil-generation stage. The C28/C29 steranes ratio suggest that the central oilfields of the Persian Gulf have Paleozoic and Jurassic source rocks, whereas the Sarvak reservoir in other parts of this region is sourced from Cretaceous carbonate rocks.

Integration of geoscience data to delineate quality of the Asmari reservoir, Iranian part of the Persian Gulf basin

The Hendijan Field is an asymmetric structure located in the northwestern Persian Gulf and consists of several oil and gas-bearing intervals. Oligocene to Miocene successions in the field host large volumes of hydrocarbons. The Asmari Formation comprises the mixed siliciclastic and carbonate members formed in a shallow marine carbonate ramp depositional environment. The siliciclastic part displays the best reservoir quality within the Asmari Formation. Through petrophysical, sedimentological, and geophysical analysis, this study divides the Asmari Formation into six, third-order depositional sequences. By doing so, it clarifies the relationships between depositional sequences and reservoir characteristics, particularly porosity and water saturation. Detailed petrographical analysis, core description, well log analysis, and seismic interpretation distinguish eight microfacies, two petrofacies, and six third-order sequences within the Asmari Formation. 3D reservoir-property models are developed that incorporate elements of the sequence stratigraphical framework. Within the six identified sequences, high reservoir quality zones are associated with AS-4 and AS-5, which comprise mostly grain-supported lithologies associated with shoal facies. The supratidal, intertidal, and lagoonal facies of AS-2, which are often associated with the occurrence of anhydrite and mud-supported fabrics, reflect lower reservoir quality. Hydraulic flow units (HFU) are delineated to assist in characterizing reservoir heterogeneity and porosity/permeability prediction. Five HFU were identified by applying the flow-zone-indicator method to evaluate reservoir quality. Both the transgressive system tract (TST) of AS-2 and early TST plus late highstand system tract (HST) of AS-6 contain elements of HFU-A. The most productive units of AS-4 and AS-5 belong to HFU-E.

Glyptothorax sardashtensis, a new species of torrent catfish from the upper Lesser Zab drainage in Iran (Teleostei: Sisoridae).

Glyptothorax sardashtensis, new species, from the upper Lesser Zab in Iran, is distinguished from its congeners in the Persian Gulf basin by: a plain flank without black or brown blotches; a wide and round anterior margin of the medial pit in the thoracic adhesive apparatus; few, short median striae in the thoracic adhesive apparatus; three yellowish blotches arranged in a crescent-shaped arch on the nuchal plate in front of the dorsal-fin origin; no tubercles on the head and flank; and a short adipose fin. The new species is also distinguished by a minimum K2P sequence divergence of 2.16% in the mtDNA-COI barcode region from G. daemon and G. galaxias, its closest relatives. Glyptothorax kurdistanicus is re-discovered close to its type locality.