High-resolution 3D Seismic Data Research Articles

Controls On the Geometry And Evolution of Humid-Tropical Fluvial Systems: Insights From 3D Seismic Geomorphological Analysis of the Malay Basin, Sunda Shelf, Southeast Asia

Abstract High-resolution three-dimensional (3D) seismic reflection data from the Pleistocene-to-Recent succession of the Malay Basin (Sunda Shelf, SE Asia) have been used to evaluate the geometry, dimensions, distribution, and evolution of humid-tropical fluvial channel systems. Based on their seismic expression and variations in sinuosity and depth, we identify six fluvial channel types, which occur in eight, seismically defined, 18–145-m-thick depositional units. Each unit is characterized by a consistent vertical change in channel-body geometry and dimensions as follows (bottom to top): (1) relatively large (300–3000 m wide and 15–45 m deep), straight to low-sinuosity channels and/or large incised valleys at their bases, and (2) smaller (75–250 m wide and 8–23 m deep), highly sinuous channels at their tops. This cyclical stratigraphic architecture is interpreted as a mainly climatically driven change in fluvial discharge and sediment supply, rather than by eustatically or tectonically driven changes in relative sea level based on (i) the study area was located far upstream (ca. 700 km) of the coeval shoreline, and (ii) tectonically quiescent nature of the basin during the Pleistocene to Recent. Although the upstream controls were likely the main controls on the stratigraphic organization (Units 2–4 and 6), the large incised valleys (Units 5 and 7) are interpreted to be formed due a relative sea-level fall during the Last Glacial Maximum (LGM). This study demonstrates how an improved understanding of the temporal and spatial variability of fluvial channel systems can be obtained through detailed analysis of regionally extensive, high-resolution 3D seismic reflection data. In particular, regional constraints on channel geometry, scale, and orientation can be more confidently determined than is typically permitted by deeper, lower-resolution subsurface data. Furthermore, we have provided quantitative constraints on the dimensions, geometries, and paleohydrology of humid-tropical fluvial systems, which form significant, but generally less well-imaged, hydrocarbon-bearing reservoirs, in the more deeply buried parts of the Malay Basin and in many other basins around the world.

The spatial, temporal and volumetric analysis of a large mud volcano province within the Eastern Mediterranean

This paper documents and describes through the use of 3D seismic data a prolific mud volcano province within the Eastern Mediterranean. As many as 386 mud volcanoes were mapped within the post-salt succession of the western slope of the Nile Cone, offshore Egypt, using high resolution 3D seismic data. The mud volcanoes within this field display significant geometrical variability in diameter (c. 550 m to c. 5660 m), height (c. 25 m to c. 510 m) and volume (c. 0.1 km3 to c. 3.3 km3) and lie at depths ranging from c. > 6000 m subsea to c. 3100 m at the seafloor. A close spatial relationship between mud volcanoes and base-salt depressions and regions of anomalous thinning within the immediate pre-salt succession, combined with documented core samples taken from mud volcanoes within this region present a powerful argument for a pre-salt source of mud. 3D seismic interpretation and volumetric analysis of these mud volcanoes and their source region permit the definition and quantification of their depletion zones. A conceptual model for a dynamic liquefaction and sediment withdrawal process is proposed whereby mud is fed into a central conduit as the depletion zone propagates radially and episodically outwards resulting in a the formation of a concentric depletion zones. Prolonged mud volcanism within this region over the last ∼5.3 Ma implies the potential for long lived pre-salt overpressure and continued mud volcanism following the catastrophic hydrodynamic impact of the Messinian Salinity Crisis. It is suggested that the scale of mud volcanism means that this region should be considered as among the largest mud volcano provinces in the world.

Arctic megaslide at presumed rest.

Slope failure like in the Hinlopen/Yermak Megaslide is one of the major geohazards in a changing Arctic environment. We analysed hydroacoustic and 2D high-resolution seismic data from the apparently intact continental slope immediately north of the Hinlopen/Yermak Megaslide for signs of past and future instabilities. Our new bathymetry and seismic data show clear evidence for incipient slope instability. Minor slide deposits and an internally-deformed sedimentary layer near the base of the gas hydrate stability zone imply an incomplete failure event, most probably about 30000 years ago, contemporaneous to or shortly after the Hinlopen/Yermak Megaslide. An active gas reservoir at the base of the gas hydrate stability zone demonstrate that over-pressured fluids might have played a key role in the initiation of slope failure at the studied slope, but more importantly also for the giant HYM slope failure. To date, it is not clear, if the studied slope is fully preconditioned to fail completely in future or if it might be slowly deforming and creeping at present. We detected widespread methane seepage on the adjacent shallow shelf areas not sealed by gas hydrates.

Submarine channel evolution, terrace development, and preservation of intra-channel thin-bedded turbidites: Mahin and Avon channels, offshore Nigeria

Terraces on the modern seafloor are defined as topographically flat areas above the active submarine channel thalweg but within the confines of the channel-belt. They have been described from many modern submarine channels, but the controls on terrace distribution, evolution and stacking patterns are not well understood. In this study, we describe the architecture of the Mahin and Avon channel-belts and their associated terraces, located offshore Nigeria towards the northwest of the Niger Delta. The studied channel sections are <10km apart up-dip and converge downslope. They are on slopes with similar gradients, yet they have significantly different morphologies indicating that the interplay between sedimentary processes and channel evolution must be different.The surfaces defining the bases of the terrace bodies have been mapped along both channels using high-resolution 3D seismic data. Spectral decomposition of the data reveals subtle variations in seismic character that highlight sedimentological detail that can otherwise not be recognized, allowing us to suggest the processes responsible for terrace formation and terrace body composition.The contrasting evolution of the two channels is reflected in the morphology and architecture of their terraces. While the Mahin terrace bodies show a predictable pattern, typically consisting of stacked channel-fill and overbank deposits in a circular planform shape (shape controlled by cut-off channel bends), the deposits of the Avon terrace bodies up-dip of the confluence with the Mahin are dominated by overbank deposits, with the planform terrace shape heavily controlled by the topography of the underlying channel-belt deposits.This study shows how spatially and temporally associated channels can have markedly different architectures. The evolution of the channel and the abundance and stacking patterns of compositional elements within terrace bodies are shown to be linked.

High-resolution seismic geomorphology and stratigraphy of a tunnel valley confined ice-margin fan (Elsterian glaciation, Southern North Sea)

The deep Middle Pleistocene subglacial incisions of the Southern North Sea (SNS) are commonly infilled by northward gently dipping clinoforms oriented toward the former ice-sheet core. We have focused on the terminal sector of the largest tunnel valley (TV) of the SNS and offer the first high-resolution reconstruction of the geomorphology and stratigraphy of the infill of the glacial incision, as well as the detailed geomorphology of the incision to better understand the genetic mechanisms of these uncommon but peculiar large-scale (up to 13 km in length) bedforms. For this study, high-resolution 3D seismic data, the grain-size distribution from ditch cutting samples, and the gamma-ray wireline log of borehole K14-12 are used. The TV formed in the subglacial environment by steady state flows in a time-transgressive fashion. Meltwater flow transports the eroded material southward and eventually deposits it at the ice-sheet margin, in the lightly grounded ice-sheet environment where the adverse slope forces the flow to wane. The process results in an elongated ice-margin fan made of clinoforms, whose grain-size distribution fines progressively southward, in the downstream direction. The formation and filling of the TV occurred during the retreat of the ice-sheet margin and cyclic fluctuations of the meltwater mass flow rate, which affected the internal stratigraphy and created an undulated top of the clinoforms’ unit. Sparsely distributed, horizontally layered units interpreted as distal proglacial lacustrine deposits filled depressions on the top of the clinoforms-bearing unit. The sequence was then sealed by a chaotic seismic-stratigraphic unit that probably belongs to postglacial times. The ice-sheet-oriented clinoforms were thus formed by sustained meltwater flow resulting from large-size Scandinavian and British convergent ice sheet flows in the freshwater environment of SNS developed between the complex ice margins and the topographic highs inherited from continental Europe.

Submarine landslides, relationship with BSRs in the Dongsha area of South China Sea

AbstractGas hydrate samples were first obtained in the Dongsha area, South China Sea (GMGS2) in 2013. High-resolution 3D seismic data in the area show various small landslide bodies developed as huge mass transport deposits. These bodies are divided into seven types on the basis of their shapes, internal structures and geneses (slide, collapse and deformation above BSRs, as well as the slump wedge, lens, block and sheet below BSRs). Based on this classification, detailed studies were conducted, including measurements of the slump body sizes and slope gradients of landslides, depiction of their three-dimensional characteristics, and research on the landslide distribution. To determine the genetic differences of these seven types, this study analyses the possibility of vertical flow-pattern-transformation and mechanisms of submarine landslide formation. Results show that the dominant factor influencing the submarine landslides in the Dongsha area is the free gas emitted from gas hydrate decomposition, with possible transformation between flow patterns. Finally, there are two kinds of relationships between submarine landslides and BSRs since the free gas either influences the submarine landslide bodies below or above BSRs, resulting in two types of submarine landslide body associations: Type A is characterized by submarine slide above BSRs and slump lens below BSRs, whereas Type B shows deformation above BSRs and slump blocks below BSRs. Type A is favourable for gas exploration because it indicates less decomposition and better sealing of gas hydrate layers.

Submarine erosional troughs in the northern South China Sea: Evidence for Early Miocene deepwater circulation and paleoceanographic change

The paleoceanography of the South China Sea (SCS) is poorly understood, although recent cruises and an ODP expedition (Leg 184) have provided a useful general framework. Here we report previously unrecognized multi-km scale sedimentary structures consisting of coupled ridges and troughs within the Early Miocene strata, using high-resolution 3D seismic data from the northern SCS margin. The troughs are interpreted as linear and/or arcuate erosional features which truncate the underlying strata. They range in orientation from E-W in the southern part of the study area to nearly NE-SW in the northwestern part of the study area. The spacing of erosional troughs varies from less than 0.1 km in the southern part to more than 3 km in the northern part, and they are about 50–1500 m in width, with a relief of 10–90 m. The erosional troughs are parallel to the regional strike of the Early Miocene slope of the northern SCS. From their internal geometry, context, regional distribution and most importantly their orientation relative to the paleo-slope gradient at the time of their formation, it is argued that they formed due to the action of bottom currents linked to the broader paleo-circulation regime in the basin. We infer that the paleo-bottom currents intruding from the Pacific flowed along the northern SCS slope, resulting in the occurrence of localized erosional troughs as deep water masses impinged on and interacted with the sea floor topography. This study provides new insights into the Early Miocene paleoceanography of the SCS and demonstrates the utility of 3D seismic data to enhance our understanding of paleo-bottom current circulation regimes.

Mesozoic reactivated transpressional structures and multi-stage tectonic deformation along the Hong-Che fault zone in the northwestern Junggar Basin, NW China

The recognition of paleo-strike-slip faulting is often difficult, particularly when the associated structures are presently inactive and covered by thick sediments. Fortunately, high-resolution 3D seismic reflection data can provide a powerful tool to solve this problem. In this study, we focus on the structural features and tectonic evolution of Hong-Che fault system, a paleo-strike-slip fault zone recognized in the NW margin of Junggar Basin by using the 2D and 3D seismic data. The results of our analysis demonstrate that: 1) The Middle Triassic to Jurassic dextral transpressional structures were developed along Hong-Che fault zone, which are characterized by the restraining bend on the southern segment, the highly localized shearing deformation on the central segment, and the horsetail splay faulting of a fault tip zone on the northern segment; 2) The Hong-Che fault zone had also experienced the Early Permian rifting and the Late Permian-Early Triassic tectonic inversion, which probably played important roles in controlling the subsequent tectonic deformation; and 3) The demonstrated dextral strike-slip faulting is consistent with the Middle Triassic-Jurassic deformation in the Ke-Bai, Wu-Xia, and Irtysh fault zones, and therefore supports the counterclockwise rotation of Junggar Basin, which might be the far-field effect of the collision between Qiangtang block and Songpan–Ganzi terrane in the Triassic. The results of this study also prove that high-resolution seismic reflection data can serve as a useful tool for investigating the buried paleo-structures.

High-resolution 3D seismic reflection imaging across active faults and its impact on seismic hazard estimation in the Tokyo metropolitan area

We collected and interpreted high-resolution 3D seismic reflection data across a hypothesized fault scarp, along the largest active fault that could generate hazardous earthquakes in the Tokyo metropolitan area. The processed and interpreted 3D seismic cube, linked with nearby borehole stratigraphy, suggests that a monocline that deforms lower Pleistocene units is unconformably overlain by middle Pleistocene conglomerates. Judging from structural patterns and vertical separation on the lower–middle Pleistocene units and the ground surface, the hypothesized scarp was interpreted as a terrace riser rather than as a manifestation of late Pleistocene structural growth resulting from repeated fault activity. Devastating earthquake scenarios had been predicted along the fault in question based on its proximity to the metropolitan area, however our new results lead to a significant decrease in estimated fault length and consequently in the estimated magnitude of future earthquakes associated with reactivation. This suggests a greatly reduced seismic hazard in the Tokyo metropolitan area from earthquakes generated by active intraplate crustal faults.

Gas hydrate and free gas detection using seismic quality factor estimates from high-resolution P-cable 3D seismic data

We have estimated the seismic attenuation in gas hydrate and free-gas-bearing sediments from high-resolution P-cable 3D seismic data from the Vestnesa Ridge on the Arctic continental margin of Svalbard. P-cable data have a broad bandwidth (20–300 Hz), which is extremely advantageous in estimating seismic attenuation in a medium. The seismic quality factor (Q), the inverse of seismic attenuation, is estimated from the seismic data set using the centroid frequency shift and spectral ratio (SR) methods. The centroid frequency shift method establishes a relationship between the change in the centroid frequency of an amplitude spectrum and the Q value of a medium. The SR method estimates the Q value of a medium by studying the differential decay of different frequencies. The broad bandwidth and short offset characteristics of the P-cable data set are useful to continuously map the Q for different layers throughout the 3D seismic volume. The centroid frequency shift method is found to be relatively more stable than the SR method. Q values estimated using these two methods are in concordance with each other. The Q data document attenuation anomalies in the layers in the gas hydrate stability zone above the bottom-simulating reflection (BSR) and in the free gas zone below. Changes in the attenuation anomalies correlate with small-scale fault systems in the Vestnesa Ridge suggesting a strong structural control on the distribution of free gas and gas hydrates in the region. We argued that high and spatially limited Q anomalies in the layer above the BSR indicate the presence of gas hydrates in marine sediments in this setting. Hence, our workflow to analyze Q using high-resolution P-cable 3D seismic data with a large bandwidth could be a potential technique to detect and directly map the distribution of gas hydrates in marine sediments.

三维地震勘探技术在南海的应用进展及展望

随着深水油气资源勘探开发的快速增长，深海高分辨率三维地震资料精细处理和深度处理技术越来越成熟。本文对三维地震勘探技术在南海资源勘探开发中的应用进行了总结，从海底资源勘探开发、水深地形地貌反演、深水地质灾害识别评估三个方面进行了论述，并提出了目前研究工作中尚未解决的问题及未来的发展方向和研究重点。对促进和丰富我国深海三维地震资料的深度处理与应用，深入研究和认识深海沉积与工程环境具有重要意义。 High resolution 3D seismic data of deep sea was becoming more mature with the rapid develop-ment of oil and gas exploration. In this paper, we systematically analyzed and discussed the present research concerning application progress of 3D seismic exploration technology in the South China Sea on exploration and development of marine resources, inversion of deep water depth, and identification and assessment of geological hazard in deep water. Otherwise, we put forward the unsolved problems presently, the research direction and emphasis in future. This work was instructive to promoting and enriching the deep processing and application of 3D seismic data in deep sea, and has great value of further studying and understanding sediment and engineering environment in deep sea.

Iceberg ploughmarks in the SW Barents Sea imaged using high-resolution P-Cable 3D seismic data

Iceberg ploughmarks are common features of glaciated continental margins worldwide. They form when iceberg keels plough through sediments on the ocean floor. They occur in various sizes and shapes, but generally exhibit a linear or curvilinear geometry. The SW Barents Sea is a heavily glaciated margin and its seafloor shows numerous ploughmarks among other glacial landforms (Andreassen et al. 2008). We present seafloor features formed during the late Weichselian glaciation (Solheim et al. 1990) imaged using high-resolution P-Cable 3D seismic data. P-Cable 3D seismic data have a spatial resolution of 6×6 m which is better than many hull-mounted multibeam systems, particularly in deep water. However, the cumulative seismic response of the seafloor is slightly different due to the lower-frequency bandwidth (30–350 Hz) of P-Cable compared to multibeam systems (up to 500 kHz). In addition, amplitude information is readily available and complements grid-based interpretations. Numerous linear and curvilinear depressions occur on the seafloor near …

Oblique reactivation of inherited fabrics in rift basins: applications to the Northern Carnarvon Basin

Rift basins are typically developed on heterogeneous continental crust. Inherited basement fabrics exert a fundamental control rift basin geometry, and on the geometry of individual faults. Many rift basins are also the result of multiple rift episodes and early formed structures will exert further control on the way in which faults evolve in subsequent rift events.Inherited fabrics and fault reactivation are often invoked to explain rift orientation and segmentation, often with little independent evidence for their existence. However analogue models of orthogonal and oblique rifts show that predictable fault patterns result from the partitioning of stress between pre-existing structures and superimposed extension directions.The Northern Carnarvon Basin provides an ideal laboratory in which to test these models. High resolution 3D seismic data allows detailed imaging of fault patterns developed during separate Lower-Middle Jurassic and Lower Cretaceous rift events. Fault patterns clearly reveal the influence of older structures, most likely related to Carboniferous and Permian rifting, enabling contemporaneous stress patterns to be revealed.

The limits of seaward spreading and slope instability at the continental margin offshore Mt Etna, imaged by high-resolution 2D seismic data

Mount Etna is the largest active volcano in Europe. Instability of its eastern flank is well documented onshore, and continuously monitored by geodetic and InSAR measurements. Little is known, however, about the offshore extension of the eastern volcano flank, defining a serious shortcoming in stability models. In order to better constrain the active tectonics of the continental margin offshore the eastern flank of the volcano, we acquired a new high-resolution 2D reflection seismic dataset. The data provide new insights into the heterogeneous geology and tectonics at the continental margin offshore Mt Etna. The submarine realm is characterized by different blocks, which are controlled by local- and regional tectonics. A compressional regime is found at the toe of the continental margin, which is bound to a complex basin system. Both, the clear link between on- and offshore tectonic structures as well as the compressional regime at the easternmost flank edge, indicate a continental margin gravitational collapse as well as spreading to be present at Mt Etna. Moreover, we find evidence for the offshore southern boundary of the moving flank, which is identified as a right lateral oblique fault north of Catania Canyon. Our findings suggest a coupled volcano edifice/continental margin instability at Mt Etna, demonstrating first order linkage between on- and offshore tectonic processes.

3D seismic interpretation of the depositional morphology of the Middle to Late Triassic fluvial system in Eastern Hammerfest Basin, Barents Sea

Integration of seismic, well and outcrop analog data provided realistic definition of the depositional morphology of the Snadd Formation in the Eastern Hammerfest Basin, Barents Sea. In this work the morphology of the depositional system was analyzed by using acoustic impedance seismic attribute on a high-resolution 3D seismic data. Five horizon slices were interpreted between the Snadd and Fruholmen Formation. Information about lithology and environment of deposition was inferred from wireline logs and by correlation to analogs of the De Geerdalen Formation in Spitsbergen and Snadd Formation in the NE Barents Sea. The Middle to Late Triassic sediments in the study area were deposited by a meandering fluvial system characterized by depositional forms such as flood plains, point bars, levees, overbank deposits and crevasse splays. In the southwest and the northeastern part of the seismic cube, the meandering channel is divided into low and high sinuosity channels, respectively. Sinuosity of the channel is related to the paleo topography of the Middle Triassic unit (S2) with sediment source area and flow direction being from the higher areas in the southwest to low areas in the northeast. This work shows that the Middle to Late Triassic sediments in the study area were possibly sourced from the southwestern part of the present-day Barents Sea in regions correlated to the Baltic and Uralian highs.

Use of seismic attributes for sediment classification

A study to understand the relationships between seismic attributes extracted from 2D high-resolution seismic data and the seafloor's sediments of the surveyed area. As seismic attributes are features highly influenced by the medium through which the seismic waves are propagated, the authors can assume that it would be possible to characterise the geological nature of the seafloor by using these attributes. Herein, a survey was performed on the continental margin of the South Shetland Islands in Antarctica, where both 2D high-resolution seismic data and sediment gravity cores samples were simultaneously acquired. A computational script was written to extract the seismic attributes from the data, which have been statistically analysed with clustering analyses, such as principal components analysis, dendrograms and k-means classification. The extracted seismic attributes are the amplitude, the instantaneous phase, the instantaneous frequency, the envelope, the time derivative of the envelope, the second derivative of the envelope and the acceleration of phase. Statistical evaluation showed that geological classification of the seafloor's sediments is possible by associating these attributes according to their coherence. The methodologies here developed seem to be appropriate for glacio-marine environment and coarse-to-medium silt sediment found in the study area and may be applied to other regions in the same geological conditions.

Slicing and dicing HR seismic acquisition: Varied approaches to delivery of high-resolution 3D seismic data volumes for drilling-hazard studies

Experiences are described in delivering high-resolution 3D (HR3D) volumes to support the definition of drilling hazards for exploration and development drilling in different geologic settings around the world using differing levels of acquisition and processing intensity. The robustness of the HR3D approach delivers high-resolution volumetric imaging for the study of potential drilling hazards. Through acquisition trials and processing simulations, starting with a single-streamer, single-source approach to acquisition of HR3D, data can be delivered at equivalent effort to standard HR2D approaches but as a volume that allows all the advantages of 3D spatial analysis to be applied. Increasing the acquisition intensity increases the quality of the final processed volume and allows more advanced analysis approaches to be applied to the data. Use of multistreamer and multisource approaches offers the opportunity to improve acquisition efficiency with careful consideration of spread designs to maintain high frequencies without introducing directivity effects into the final data. In cases in which there is a need for HR data to support drilling-hazard or development studies, there is now no reason to not always acquire HR3D data. Similarly, in the processing of HR3D data, the full power of modern processing approaches, up to and including prestack depth migration, can be applied to provide further improvements in imaging in complex geologic settings to the benefit of drilling-hazard identification and ongoing improvements to drilling safety and operational integrity.

Canyon-related undulation structures in the Shenhu area, northern South China Sea

The characteristics and origin of seafloor and subsurface undulations were studied in the Shenhu area, northern South China Sea using high-precision multibeam bathymetric map and high-resolution 2D seismic data. Two undulation structure fields associated with submarine canyons have been identified. One structure field is developed in canyon head areas and shows waveform morphology on the bathymetric map. The waves display wavelengths and wave heights of 1–2 km and 20–50 m, respectively, generally occur on slopes from 1° to 5°, and extend for about 15 km approximately parallel to the canyon’s orientation. The other structure field is developed in the lower segment or mouth area of submarine canyons. In general, the waves display wavelengths and wave heights of 1.3–3.6 km and 50–80 m, respectively, occur on slopes of approximately 2°, and extend for more than 20 km. Sediment cores from crests between submarine canyons in the lower segment include predominantly silts and clayey silts. Since undulations in the two fields show differences in morphology and internal architectures, two different formation mechanisms are suggested. Seafloor undulations in the head area of submarine canyons are interpreted as creep folds induced by soft sediment deformation. Undulation structures in the lower segment or the mouth area of submarine canyons are sediment waves constructed by turbidity currents overflows along the submarine canyons.

CFD simulation on the generation of turbidites in deepwater areas: a case study of turbidity current processes in Qiongdongnan Basin, northern South China Sea

Turbidity currents represent a major agent for sediment transport in lakes, seas and oceans. In particular, they formulate the most significant clastic accumulations in the deep sea, which become many of the world’s most important hydrocarbon reservoirs. Several boreholes in the Qiongdongnan Basin, the northwestern South China Sea, have recently revealed turbidity current deposits as significant hydrocarbon reservoirs. However, there are some arguments for the potential provenances. To solve this problem, it is essential to delineate their sedimentary processes as well as to evaluate their qualities as reservoir. Numerical simulations have been developed rapidly over the last several years, offering insights into turbidity current behaviors, as geologically significant turbidity currents are difficult to directly investigate due to their large scale and often destructive nature. Combined with the interpretation of the turbidity system based on high-resolution 3D seismic data, the paleotophography is acquired via a back-stripping seismic profile integrated with a borehole, i.e., Well A, in the western Qiongdongnan Basin; then a numerical model is built on the basis of this back-stripped profile. After defining the various turbidity current initial boundary conditions, including grain size, velocity and sediment concentration, the structures and behaviors of turbidity currents are investigated via numerical simulation software ANSYS FLUENT. Finally, the simulated turbidity deposits are compared with the interpreted sedimentary bodies based on 3D seismic data and the potential provenances of the revealed turbidites by Well A are discussed in details. The simulation results indicate that a sedimentary body develops far away from its source with an average grain size of 0.1 mm, i.e., sand-size sediment. Taking into account the location and orientation of the simulated seismic line, the consistence between normal forward simulation results and the revealed cores in Well A indicates that the turbidites should have been transported from Vietnam instead of Hainan Island. This interpretation has also been verified by the planar maps of sedimentary systems based on integration of boreholes and seismic data. The identification of the turbidity provenance will benefit the evaluation of extensively distributed submarine fans for hydrocarbon exploration in the deepwater areas.

Focused fluid flow systems and their implications for hydrocarbon and gas hydrate accumulations in the deep-water basins of the northern South China Sea

The types, influencing factors and their evolutions of focused fluid flow systems in the northern South China Sea (SCS) are deeply studied based on high-resolution 3D and 2D seismic data. These systems include mud volcanoes, mud diapirs, gas chimneys, pipes, polygonal faults and tectonic faults. They are influenced by both tectonism and sedimentation. The gas chimneys, mud diapirs and mud volcanoes may have relationship of unidirectional evolution and we can separate them from whether the sediments are involved and whether the sediments or fluids erupt into the seawater or not. Finally, a development model of focused fluid flow systems in the northern SCS is proposed. Because their great importance for the deep-water resource exploration (hydrocarbon and gas hydrate), they should receive much attention from now on.