Shelf Of Vietnam Research Articles

Holocene sedimentary distribution and morphological characteristics reworked by East Asian monsoon dynamics in the Mekong River shelf, South Vietnam

The distribution of Holocene sediments in the Mekong River shelf area was investigated using shallow seismic and core data. The results show that the shelf depositional stratigraphy since the last glacial period can be classified into four depositional units (U1, U2, U3 and U4). The average thickness of the Holocene deposit in the nearshore area of the Mekong River estuary is approximately 20 m and decreases seaward. In addition to a thickened deposit in the palaeo-river channel, two sedimentary centres have developed, namely, the Mekong River estuary and the Cape Ca Mau area. In contrast to nearshore deposition, the Holocene sedimentation rate rapidly decreased offshore, even in the transgressive systems tract. To understand the driving mechanisms for the variation in Holocene deposition, a three-dimensional numerical model and Geographic Information System(GIS)-based model were applied to reconstruct the oceanographic and sediment transport patterns on the South Vietnam shelf. The simulation results reveal that the Mekong River shelf has undergone significant transformations since the Last Glacial Maximum (LGM). During the LGM, the coastline was situated near the shelf break, and as the sea level rose rapidly, the shoreline retreated. When the sea level reached its peak, the modern Mekong Delta emerged. Furthermore, the distribution of Holocene deposits is controlled by monsoon-influenced seasonal variations in currents, resulting in a triangular delta and narrow strip-like subaqueous clinoform. Our simulation results also show obvious erosional capacity in the offshore area, leading to an evident erosional through to the east of Cape Ca Mau and erosion of Pleistocene sediments in the shelf break area. By combining stratigraphic interpretation and oceanographic simulations, our study provides new insights into sediment transport and erosion processes mediated by ocean currents driven by East Asian monsoons.

Seasonal variations of coastal trapped waves (CTWs)’ propagation in the south China sea

Coastal trapped waves (CTWs) are sub-inertial waves with energy confined to the continental shelf and play a crucial role in the coastal dynamics. In this study, we focus on analyzing the seasonal characteristics of CTWs in the South China Sea shelf region by using observations from tide gauges and reanalysis data. Our findings reveal significant seasonal variations in both the phase speed and amplitude of CTWs in the South China Sea. It is shown that phase speed tends to be higher during the winter, followed by spring and autumn, and with less distinct propagation characteristics during the summer. In terms of amplitude, apart from seasonal variations, the CTW amplitudes on the narrower Vietnam shelf are relatively smaller. Drawing on classical theories, we analyze the Kelvin wave mode, the first shelf wave mode, and the second shelf wave mode in CTWs, and investigate the effects of winds, background currents, and stratification. Results indicate that the winds have a significant impact on the generation of CTWs, and the greatest influence of winds occurs upstream relative to the direction of CTW propagation. Background currents can have a significant impact on the phase speed of CTWs, and the seasonal variations of CTWs are closely linked to the background circulations. Additionally, we discuss the influence of seawater stratification on the phase speed of CTWs (measured by Burger number, Bu). Under conditions of strong stratification in the summer, the Bu is larger and leads to higher phase speed of CTWs, particularly when the Bu reaches its maximum on the continental slope. This study provides a better understanding of the CTWs dynamics in the South China Sea shelf region. Our findings can be useful for predicting and managing coastal hazards in the region.

Reservoir properties of effusive rocks of the Muradkhanli field (Azerbaijan)

The presence of oil accumulations in igneous rocks has been known for quite a long time. Geologists estimate that oil reserves in eruptive and weathered metamorphic rocks reach 1 % of the world’s proven oil reserves. At the Shaimskoye field (Western Siberia), oil is found in the weathered granites of the basement. Oil has been found in eruptive rocks in Texas (USA) fields, the most famous of which is the Litton Springs field. Oil is found in metamorphosed shales in the western part of the Los Angeles basin, the porosity of which is caused by the development of cracks in the roof of crystalline shales. Petroleum is extracted from serpentinites in Cuba. Basic igneous rocks contain petroleum at the Ferbro field in Mexico.At the Khukhrinsky gas field, which islocated at the north-western end of the Dnieper-Donets depression, the crystalline basement rocks are oil and gas bearing, from which commercial hydrocarbon inflows have been obtained. In the White Tiger field (Bach Ho), located on the southern shelf of Vietnam, commercial oil accumulations are also found in crystalline basement rocks.
 At the Muradkhanli field in Azerbaijan, the industrial accumulation of petroleum belongs to the igneous rocks of the Upper Cretaceous age. The natural oil and gas reservoir of the Muradkhanli field is confined to the erosion zone of the upper part of the section of these rocks.
 This work aims to determine the reservoir properties of the rocks of the Muradkhanli deposit, which belong to igneous rocks, in different ways.
 The method of estimation of final oil recovery of complex structure reservoirs was proposed for useful capacity and oil recovery of homogeneous media; different variants of the volumetric method were used for reservoirs with complex structures of pore space filling a complex and heterogeneous natural reservoir; values of hydrocarbon reserves of increased and secondary capacity were calculated for the study interval; distributions of oil reserves with right-sided asymmetry, where Mo<Me<X, were presented; it was determined that in effusive cores oil saturation and fluid filtration are caused by tectonic fracturing and cavernousness.
 Permeability varies in a wide range: 0.73·10–15—1.31·10–15 m2; the largest specific fraction of crack density is in the range 0—0.1 cm/cm2, the average value is 0.29 cm/cm2, with crack depth they decrease from 0.9 to 0.1 cm/cm2.
 The studies have shown that the natural reservoir of oil and gas in the Muradhanli field is associated with the erosion zone of the upper part of the igneous rock section.

Geological setting of the Phu Khanh Basin based on updated geological-geophysical data

The Phu Khanh Basin is a Tertiary sedimentary basin located in deep a water area adjacent to the continental shelf of Central Vietnam, which has been begun to form since the Eocene(?)/Oligocene to the Quaternary. This area has previously only been briefly studied based on satellite magnetic, gravity data and some 2D multichannel seismic lines. In this article, the authors present the most recently interpreted and merged gravity data to update the research results on geological structure, tectonics and the history of geological evolution of the Phu Khanh Basin, which are considered significant contributions for hydrocarbon exploration campaigns in the future. Our new results show that mechanism of the the Phu Khanh Basin formation was started by a rifting process with most of it located in the central basin, controlled by four main fault systems, including the NW - NE system, the NE - SW system, sub-meridian system and less active is the sub-latitude system. The evolution of the basin has undergone through four main phases of different tectonic deformation, which are characterized by its typical geodynamic regimes and tectonic activities. These evolutionary phases can be briefly described as follows: (i) Paleocene peneplanation phase, (ii) The active rifting phase in Eocene/Oligocene-Early Miocene, (iii) The Middle Miocene thermal subsidence phase and finally (iv) The Late Miocene-Quaternary shelf building phase. However, the issue of determining the Eocene age at the bottom of the basin has so far remained unclear and elucidated by the lack of deep wells penetrating the deepest region of the basin.

Characteristics of Stratigraphy and sedimentation of the Phu Khanh Basin and adjacent area

The Phu Khanh Sedimentary Basin is situated in the deep-water offshore area, east of the continental shelf of Central Vietnam. This area is said to have quite good oil and gas potential, but very few geological and petroleum research projects have been carried out in the past. In this article, the authors update new research results based on new seismic interpretation and well data conducted in recent years. The obtained results show that: Stratigraphy of the Phu Khanh Basin was subdivided into 5 large sequences, including: a. Eocene(?)/Oligocene unit is mainly clastic sediments of fluvial/lacustrine, delta plain and marine environments, b. Lower Miocene stratigraphy: Includes deltaic clastic sediments and shelfal carbonates; c. Middle Miocene stratigraphy: includes delta-plain, shallow marine terrigenous sediments and shelfal carbonate, d. Upper Miocene and Pliocene - Quaternary units include continental shelf and deep-sea terrigenous sediments. Each unit of stratigraphy and corresponding sedimentary environment is related to each stage of the geological and tectonic evolution of the basin. In general, the trend changes from the fluvial/lacustrine environment to the deltaic, shelfal and deep marine environments upward. Establishing the names of the formations and the presence of the Eocene sedimentary rocks in the Phu Khanh Basin is still an open issue. More detailed data, especially well data, are needed to obtain a more convincing interpretation.

Sequence stratigraphy and evolution of the southern Central Vietnam Shelf during Late Pleistocene-Holocene

The central Vietnam continental shelf is located on the western margin of the East Vietnam Sea (South China Sea). This study provides new findings regarding the Late Pleistocene-Holocene evolution of the southern central Vietnam shelf off Binh Dinh province using high-resolution seismic profiles and sediment cores. The study found that the Late Pleistocene-Holocene sequence stratigraphic model of the study area can be divided into three systems tracts: the regressive systems tract (RST), the transgressive systems tract (TST), and the highstand systems tract (HST). The RST is the oldest and thickest of the three systems tracts and is characterized by forced regressive and lowstand deposits. These deposits likely formed between the Marine Isotope Stages (MIS) 5e highstand and the Last Glacial Maximum (LGM) termination. The RST is well-preserved at water depths deeper than 60 m and has a maximum thickness of about 40 m. The TST is the middle systems tract and was likely deposited during a postglacial transgressive period, from the LGM lowstand termination to around 8 cal ky BP. The TST is thickest in shallow water depths in the southern part of the study area and within incised-valley systems. The HST is the youngest of the three systems tracts and is dominated by thick mud clinoforms that prograde onto the shelf following mid-Holocene sea-level highstand until the present day. The HST was primarily deposited in shallow water depths of 0–50 m and decreases in thickness towards the outer shelf, ending at a water depth of around 80 m.The study also found that Late Pleistocene-Holocene relative sea-level change is the main factor controlling the overall stratigraphic organization of units on the study area. The presence of the beach-ridge structure at a water depth of approximately 140 m below the modern sea level in the southernmost part of the study area suggests that the region experienced a sea-level lowstand in the past. This lowstand was likely a result of subsidence due to a high sedimentation rate. This discovery is consistent with earlier studies conducted on the central Vietnam shelf. There are similarities in the deposition of Late Pleistocene-Holocene deposits between Binh Dinh and other shelves worldwide, indicating that there may be consistent controlling factors that govern the geological history of these regions. However, the thickness and distribution of deposits in the study area may be different due to local factors that interacted to shape the area differently than others.

Copepod vertical diel migration on the continental shelf of South Central Vietnam

Zooplankton often migrates within the water column for different purposes but mostly to find food and avoid predators. Vertical migration over 24 hours is called diel vertical migration (DVM). However, knowledge of DVM for different zooplankton species is limited. The present study analysized DVM based on species distribution in the water column at each different times of day at two stations on the central Vietnam shelf. One station was on the shelf (LT2) and another was on the shelf slope (FK002). The results showed that 69 zooplankton species, out of 191 recorded at the two stations, having strong DVM (dz > 15 m). Among them, 38 species were nocturnal and 36 species showed reverse DVM. Species with nocturnal DVM were less on the shelf station than on the shelf slope. Moreover, detailed analysis at LT2 showed 18 species having DVM at dawn and 13 species having DVM at sunrise. This study provides important data for zooplankton ecology in Vietnam and marine tropical waters.

Application of artificial neural network and seismic attributes to predict the distribution of Late Oligocene sandstones in the Cuu Long basin

Artificial neural network (ANN) has been widely applied in oil and gas exploration and production. This study presents the results of predicting the distribution of Late Oligocene sandstones in the Cuu Long basin based on the application of ANN and seismic attributes. These results have great significance, helping to orient the oil and gas prospection and exploration of the Cuu Long basin and other exploration objects on the continental shelf of Vietnam. The authors used unsupervised neural networks (UNN) and UNN methods constantly associated with the principal component analysis (PCA) to divide seismic facies. Seismic attributes such as Root mean square (RMS), Frequency, Envelope, Relative Acoustic Impedance (RAI), Phase, Sweetness, Amplitude, and t-Attenuation were analyzed and selected as input for the ANN training and testing process. These attributes can reflect changes in lithology, and sedimentary facies, from which will have a better view of the distribution of reservoirs in the study area. From 4 to 10 classes of seismic facies have been tested using each method to improve the results. Comparing the results of seismic facies classification by the UNN method and by UNN combined with PCA, it can be seen that the UNN combined with PCA will help reduce noise in seismic data better than UNN only. The research results have identified the distribution of Late Oligocene potential sandstones in the study area in the Cuu Long basin, which are mainly concentrated on the slopes of a large lake, with the direction of sediment transport from the West and Northwest.

Features of the Distribution and Genesis of Authigenic Sulfide Mineralization in Bottom Sediments on the Vietnam Shelf and the South China Sea Slope

Features of the Distribution and Genesis of Authigenic Sulfide Mineralization in Bottom Sediments on the Vietnam Shelf and the South China Sea Slope

Gasgeochemical features in the western part of the East Vietnam Sea (Bien Dong Sea)

During the joint Russian-Vietnamese studies in the East Vietnam Sea (known as Bien Dong or the South China Sea), manifestations of new hydrocarbon-accumulating zones were discovered; evidences of the presence of mineral indicators for solid minerals in shelf deposits were obtained; a unique zone, where accumulations of ferromanganese crusts and nodules have been formed, was revealed for the first time; evidence of unique properties of deep-water fine-dispersed carbonate sediments (which makes it possible to attribute them to an independent type of mineral resources of the East Vietnam Sea) were obtained; the ikaite mineral (that serves as an indicator of methane migration zones and cold marine paleo-conditions) was discovered in the Phu Khanh basin; heavy concentrates with indicators of rare forms of ore mineralization were collected; features of methane and mercury fluxes into the atmosphere, cultures of methane-oxidizing, oil-oxidizing and sulfate-reducing bacteria were registered for the first time within the study areas. New data on gravity and magnetic field anomalies along the shelf and slope of Vietnam have been obtained. The article presents the results of coastal geophysical and gasgeochemical research obtained in 2010–2020 within the Joint Russian-Vietnamese Laboratory for Marine Geosciences (POI FEB RAS - IMGG VAST). For the first time, anomalous methane fields (comparable to anomalies on the oil- and gas-bearing shelf and the gas hydrate-bearing slope of Sakhalin Island) were registered in the water column. The gravimagnetic survey was carried out on the central and southern shelf and the continental slope of Vietnam; the executed works supplemented the geophysical data, which had been obtained in the 80s–90s of the preceding century. The paper contributes to the Russia-Vietnamese program within the UN Decade of Ocean Sciences for Sustainable Development framework.

Seismic activity in the continental shelf of South-Central Vietnam and adjacent regions from 2005 to 2020

Since 2005, 10 seismic monitoring stations have been installed in the southern part of Vietnam. These stations can detail the earthquakes in the region and adjacent areas. In the past, there was an earthquake of magnitude 6.1 (1923) in the offshore South-Central Part related to the Hon Tro eruption, the largest observed earthquake magnitude in the 20th century. Between 2005 and 2020, 371 earthquakes were recorded with magnitudes ranging from 0.7 to 5.3. Most of events were distributed on some northeast-southwest direction faults in South Central offshore. The magnitude of the representative earthquake was relatively small, Mc = 2.2, so it is assumed that this research area was of weak activity. The epicenter is about < 20 km, and the majority concentration is at a relatively shallow depth of 5km and still located in the crust of Earth. The relationship between earthquake magnitude and frequency in this region is as follows: lgN = 4.063 – 0.694*M for the entire catalog of 371 events and lgN = 3.826 – 0.704*M after filtering 92 foreshocks and aftershocks of the earthquakes M = 5.3 on November 8th, 2005, and M = 5.2 on November 28th, 2007. So, the calculated average b-values before and after filtering foreshocks and aftershocks were approximately 0.7. These values are almost approximate to the b-value of 0.76 determined by Pham Van Thuc et al., (2004) based on the East Vietnam Sea earthquake catalog from 1903 to 2002 and smaller than the b-value of 0.92 for triggered earthquakes in the Song Tranh 2 hydropower region. In addition, oil and gas exploitation activities are still taking place in the South-Central continental shelf; it is necessary to continue collecting earthquake data to elucidate the causes of earthquakes in the study region.

Research on evaluating, selecting and manufacturing the VPI SP chemical product for conducting field test to enhance oil recovery coefficient of oil fields in Cuu Long basin, offshore Vietnam

The Vietnam Petroleum Institute (VPI) is implementing a multi-task national level project entitled “Research, evaluate, select and develop a pilot programme for industrial application of solutions to improve oil recovery coefficient for clastic oil bearing reservoirs of oil fields in the Cuu Long basin, on the continental shelf of Vietnam”. Specifically, detailed evaluation studies have been carried out from geological characteristics, reservoir engineering, production to EOR mechanism to develop technical criteria for the process of manufacturing and evaluating the efficiency of the chemical system to optimise the laboratory scale, propose the production and injection scenarios to optimize the development plan as well as evaluate the efficiency of increasing oil recovery coefficient on the reservoir simulation model; conduct production at pilot scale and implement industrial application testing on the field scale for clastic oil bearing reservoir, Cuu Long basin.
 The article presents the results of research, evaluation, selection and successful manufacture of a VPI SP chemical system based on the combined mechanism of anionic - non-ionic surfactants and polymers to ensure satisfying the harsh technical requirements of oil fields in Vietnam such as resistance to high temperature, high pressure, high mineralisation, very low surface tension, optimal micro-emulsion, low adsorption onto reservoir rocks, reducing residual oil saturation in the reservoir. Results of the evaluation of increased efficiency of oil recovery on actual samples of Miocene reservoir showed an increase of over 21%. The VPI SP chemical system has been included in the plan of industrial-scale testing by Vietsovpetro in Bach Ho and other producing fields in the clastic sections of the Cuu Long basin.

Variation of sediment provenance at the 09 - 1 Block, Cuu Long Basin: their significance in assessing the Oligocene - Miocene reservoir quality

The Cuu Long Basin is one of the Tertiary sedimentary basins situated on the continental shelf of Vietnam, which demonstrates the high potential of oil and gas. Apart from fractured granite reservoirs, the Oligocene - Miocene sand bodies are thought to have significant potential for forming non - structural traps. The results of the study on the composition and physical properties of the sediments derived from wells "X" and "Y", block 09 - 1, Cuu Long Basin show that there is a clear difference between the Late Oligocene and Early Miocene sandstone in the well "X", namely the Miocene sandstone shows larger particle size, higher roundness and sortness (TB: 434.2; Ro: 0.69; So: 2.22) than those of the Late Oligocene sandstone (TB: 104.28; Ro: 0.64; So: 1.46). This difference is likely attributed to the fact that the Miocene sandstone was influenced by the marine environment, which intensified the roundness and sortness. Meanwhile, the well "Y" did not show much difference in the physical parameters of the sediments between the Late Oligocene and Early Miocene age ranges. However, the grain size was slightly increased and the roundness was less during the Early Miocene. It is possible that the “Y” well is located closer to the local source. The variation in the physical parameters of the sediments, proportion of sand grains and clay minerals shows that the quality of late Oligocene reservoir is better than that of Early Miocene reservoir, and the Late Oligocene reservoir quality in the "X" well is better than that in the borehole "Y".

Origin of hydrocarbons in the Bach Ho field (The Vietnamese shelf)

This article presents the results of a geochemical study of oil on the Vietnam shelf (Cuu Long basin), including those in the crystalline basement. The Bach Ho field oils in the basement have a hydrocarbon distribution that is no different than oil of numerous accumulations in Oligocene and Miocene sedimentary sequences. Similar to the organic origin oils of the world, oils from the Bach Ho field lack regular isoprenanes С12 and С17 and cheilanthanes (tri-cyclic terpanes) С22 and С27. A distinctive feature of these oils is a large amount of cheilanthanes С19-С29, and large neo-adiantane to adiantane and hopanes to steranes ratios. All these parameters indicate a large bacterial contribution in the generation of these oils. Studies have shown the similarity between oil biomarker parameters and the organic matter of sedimentary rocks, which supports the organic nature of the oils in the basement fields on the Vietnam shelf. It is shown that the hydrocarbon accumulations in the basement complexes of the Cuu Long basin are in a secondary occurrence, and their origin was the organic matter of the sedimentary source rocks.

Integrated Geological–Geophysical and Oceanographic Research in the South China Sea: Cruise 88 of the R/V “Akademik M.A. Lavrentyev”

Abstract—The paper gives brief results of comprehensive studies in the South China Sea obtained from a joint Russian–Vietnamese expedition in November 2019 (cruise 88 of the R/V “Akademik M.A. Lavrentyev”). The set of methods included acoustics, geophysics, geology, mineralogy,geochemistry, paleogeography, geomicrobiology, hydrooptics and hydrology. The seafloor relief, geophysical and gasgeochemical fields have been refined; new features of the geochemistry and mineralogy of the continental shelf of Vietnam and the adjacent deep-sea basins have been revealed.

ЭНЕРГЕТИЧЕСКОЕ СОТРУДНИЧЕСТВО НЕФТЕГАЗОВЫХ КОМПАНИЙ РФ И ВЬЕТНАМА. ПЕРСПЕКТИВЫ И ВЫЗОВЫ

The article shows the history of the energy cooperation develop- ment between oil and gas companies (OGC) of the Russian Federation (RF) and the Socialist Republic of Vietnam (SRV) on the continental shelf of Vietnam in the South China Sea. Despite the richest reserves of natural resources and, in particular, hydrocarbons in the territory of Vietnam, slightly less than half of the potential oil reserves and about a third of the potential natural gas reserves have been explored. The desire of the Vietnamese leadership to develop rela- tions in the oil and gas sector with foreign countries has led to the attraction of foreign oil and gas companies to the search, exploration and development of oil and gas fields on the shelf of the SRV in the South China Sea. Russian oil and gas companies are among the key partners in hydrocarbon production. The article shows the spheres of cooperation between Russian and Vietnamese oil and gas companies, its prospects and risks. The authors note that not only Russian oil and gas companies operate in Vietnam, but Vietnamese oil and gas companies have also gained access to Russian fields in the Russian Federation.

Combination of methodology on researching the petroleum formation process in Lower Miocene sediments, Cuu Long Basin

The process of formation and deposition of granular sedimentary formations containing oil and gas in sedimentary basins on the continental shelf of Vietnam is a key factor in the study to determine the distribution trend, characteristics and scale of the sedimentary formations in general and Miocene sediments in particular. Up to the present time, the majority of Vietnam's oil and gas exploitation basin are distributed on continental or coastal shelves, so the study of the origin and evolution of basins in general and components in particular (into reservoir system) still exists many gaps not only with geologists but also with petroleum research and exploration company on the continental shelf of Vietnam. The samples and data collected cover most of the onshore and offshore in Southeastern Vietnam, allowing the construction of the relationship boths the two areas that have traditionally been studied by the companys, with the lack of synchronous methods, closely links. The collection of research data, recently collected, created convenient conditions for linking and comparing the evolutionary history between the continental sediments and the continental shelf through the survey of collecting field samples and core samples at petroleum exploration drill wells come to clarify the origin, evolution, the trend of sedimentary materials transporting. The methodology conducted to research includes geotectonics, stratigraphic seismic analysis, borehole geophysical analysis, stress filed, core sample analysis, sedimentary lithological analysis, biostratigraphic analysis, analysis of U-Pb zircon isotope age and at last artificial intelligence. The study results can also be used to predict the presence and distribution of the Miocene sandstone petroleum formations in researching area.

Water-free oil reservoirs: origin and morphology

The features of the morphology and composition of secondary minerals in the reservoir zones of the White Tiger (Bach Ho) deposit (shelf of South Vietnam) and deposits in clay rocks of the Bazhenov formation of the Salym area of Western Siberia are considered. It is shown that the common for these fields is the formation of a reservoir as a result of the leaching effect of high-temperature fluids. The genesis of the reservoir is determined by a complex of secondary minerals, obviously of hydrothermal origin, partially filling caverns and cracks in the rock: native silver – zincous copper – barite – anhydrite – kaolinite – laumontite (White Tiger oilfield) and sulphates of iron, aluminum, sodium and calcium – iron-aluminum alum, alunite, jarosite, mirabilite, melanterite, gypsum (deposit in the rocks of the Bazhenov formation of the Salym area). Diagnostics of secondary minerals was established based on the results of microprobe studies of undisturbed samples and analysis of the composition of water extracts from crushed core samples.The species composition of secondary minerals indicates a high temperature of the affected solutions, which varied from 600 to 200°C in the case of the White Tiger oilfield, and in the range of 350–450°C, in the case of rocks of the Bazhenov formation. Hydrothermal alteration of crystalline rocks with the formation of secondary clay minerals (kaolinite, montmorillonite, hydromica), zeolites and minerals-sulfates, which are crystalline hydrates, occurs with the absorption of huge amounts of water by the rock (up to 4∙108 tons of water per 1 km3 of altered rock). This may be related to the waterlessness (lack of bottom water) of oilfields, the reservoir of which has a hydrothermal origin. It is possible that oil deposits in crystalline rocks with high oil-saturated zones have associated waters of hydrothermal rather than sedimentogenic origin, but they occur at considerable depths and are not penetrated by drilling. This possibility is evidenced by the discovery of hydrothermal water in the basement of the White Tiger reservoir at a depth of 4493 m, which, in terms of chemical composition and mineralization, is close to the waters of sodium chloride hydrotherms of Kamchatka.

Sediment budget and morphological change in the Red River Delta under increasing human interferences

The Red River sediment dispersal system has been increasingly altered by human activities, but the resultant morphodynamic change and sediment budget in the Red River Delta (RRD) has been little studied in a holistic perspective. In this study, time-series analysis of river water and sediment discharges from 1960 to 2010 was carried out to trace human interferences on sediment routing processes, and historical charts from 1930 to 2008 were digitized to reconstruct the Digital Elevation Models for investigating spatiotemporal variations in the RRD morphology and calculating their depositional and erosional fluxes. The results show that sediment reduction by 61.3% in the Red River is mainly induced by constructing the Hoa Binh Dam at the lower reach of the Da river, and deforestation and other land-use change have recently increased significantly the sediment loads in the Thao and Lo rivers. Intertidal and subtidal morphological changes in the RRD are highly site-specific in response to natural and anthropogenic drivers. Rapid intertidal accretion majorly occurs near the distributary mouths because of abundant sediment supply and artificially promoted siltation by land reclamation projects, but severe coastal erosion may occur secularly after the distributary outlet shifting or temporarily by storm events. The subaqueous RRD is generally featured by the contour-parallel zonation of erosion and accretion determined by strong longshore currents associated with monsoon winds. Net accretion was observed in the tide-dominated northern subaqueous RRD and has recently changed into a slight erosion due to reduced sediment input in the last two decades, while net erosion was monitored in the southern subaqueous RRD predominated by wave and longshore currents and has recently entered into a slight accretion phase in response to the distributary outlet shifting and secular morphodynamic adjustment. The study RRD region received on average 41.1 Mt./yr (Mt = 106 t) of suspended sediments, and 14.2 Mt./yr and 28.6 Mt./yr were estimated to accumulate on the intertidal flats and in the northern subaqueous RRD, respectively. However, erosion in the southern subaqueous RRD could contribute 42.9 Mt./yr of sediment to the system. Therefore, 41.2 Mt./yr of suspended sediment was indicated to escape from the study RRD region and transport further southward by longshore current to form the distal muddy clinoform along the inner Vietnam shelf. This sediment budget estimation should bear a significant uncertainty, but provides important information for multi-decadal sediment dispersal in a mega-delta system and coastal management.

Preliminary assessment of the characteristics of Late Miocene - Quaternary intrusive and extrusive magmatism in the Tu Chinh - Vung May basin, southeastern continental shelf of Vietnam

Based on the seismic and well dataset provided by the Vietnam Petroleum Institute (VPI), the authors have mapped and described the characteristics of the distribution and morphology of magmatic bodies as well as relatively dated them in the Tu Chinh - Vung May basin and adjacent areas. To distinguish magmatic bodies from other amplitude anomalies such as gas zone or carbonate build-up/layers, multiple criteria were used such as cross-cutting relationship, associated deformation of surrounding strata, morphology and geological relationship between different magmatic bodies. Intrusive bodies are usually sheet-like or saucer-shaped sills that cross-cut strata and even deform overlying strata, while extrusive bodies are usually cone-shaped vents/volcanoes or extensive lava sheets that conform to strata. The magmatic bodies often distribute in clusters around one or more magmatic conduits. Middle Miocene and older syn-rift faults controlled the pathway of the conduits. Magmatic bodies are more abundant closer to the East Sea spreading margin. Late Miocene - Quaternary magmatism is widespread in the study area in particular, and in the East Sea and adjacent areas in general. These activities took place after rifting and oceanic crust formation had ended, which is characteristic of magma-poor margins.