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The continental margin of the northern South China Sea is considered to be a magma-poor rifted margin. This work uses new seismic, bathymetric, gravity, and magnetic data to reveal how extensively magmatic processes have reshaped the latter continental margin. Widespread hydrothermal vent complexes and magmatic edifices such as volcanoes, igneous sills, lava flows, and associated domes are confirmed in the broader area of the northern South China Sea. Newly identified hydrothermal vents have crater- and mound-shaped surface expressions, and occur chiefly above igneous sills and volcanic edifices. Detailed stratigraphic analyses of volcanoes and hydrothermal vents suggest that magmatic activity took place in discrete phases between the early Miocene and the Quaternary. Importantly, the occurrence of hydrothermal vents close to the present seafloor, when accompanied by shallow igneous sills, suggest that fluid seepage is still active, well after main phases of volcanism previously documented in the literature. After combining geophysical and geochemical data, this study postulates that the extensive post-rift magmatism in the northern South China Sea is linked to the effect of a mantle plume over a long time interval. We propose that prolonged magmatism resulted in contact metamorphism in carbon-rich sediments, producing large amounts of hydrothermal fluid along the northern South China Sea. Similar processes are expected in parts of magma-poor margins in association with CO2/CH4 and heat flow release into sea water and underlying strata.

Multiple natural gas fields have been discovered in the Baiyun depression and the adjoining Panyu lower uplift in the Pearl River Mouth Basin, northern South China Sea. The natural gases are associated with condensate and are characterized by relatively heavy carbon isotopes, with methane and ethane δ13C values ranging from –44.2‰ to –33.6‰ and –30.0‰ to –25.4‰, respectively. Nearly all methane and ethane are derived from oil-prone type II kerogen in the Wenchang Formation source rock, whereas the heavy hydrocarbon gases (propane, butanes, and pentanes) are derived from both the Wenchang and Enping (type III kerogen) Formations, based on an integrated comparison of carbon isotopic compositions of the natural gases, typical type I/II and type III kerogen-derived gases, and the Enping and Wenchang kerogens. The gases from the eastern parts of the Baiyun depression and the Panyu lower uplift mainly originate from secondary oil cracking and primary kerogen cracking, respectively. The gases from the northern slope of the Baiyun depression are a mixture of oil-cracking and kerogen-cracking gases. Both oil-cracking and kerogen-cracking gases were mainly generated from the Wenchang Formation source rock in the maturity range of 1.5%–2.5% vitrinite reflectance, with a corresponding present-day depth range of 5400–6500 m (17,700–21,300 ft). The apparent contribution of the Wenchang Formation to the discovered gas accumulations demonstrates that it is the most important source rock in the area, instead of the Enping Formation. The search for more gas derived from oil cracking will be the next natural gas exploration direction in the Baiyun depression.

High-resolution seismic and borehole data were used to characterize a volcanic mound in the northern South China Sea, including its internal architecture, lithological characteristics and evolutionary history. On seismic profiles, the mound shows a convex geometry similar to an isolated carbonate buildup. It was therefore previously seen as a carbonate buildup and a significant hydrocarbon target until an industrial well BY7-1 proved its volcanic nature. Ten seismic facies are identified to analyze the internal architecture of the mound under the constraint of borehole data. Petrologic analysis based on cuttings and thin sections reveals that the mound is composed of volcanic tuffs, siliciclastics, carbonates, and basalt layers. Depositions and architecture of the mound are interpreted as a result of an interplay between tephra accumulation during volcanic eruptions, wave-induced re-deposition of volcaniclastics when the volcanic mound emerged above sea level, and subsequent siliciclastic/carbonate deposition when the volcanic mound was flooded during the phases of volcanic quiescence. Furthermore, the correlation of seismic and well data allows us to reconstruct the entire evolutionary history of the mound from its formation to its demise and final burial. This work presents a detailed description of the mound architecture and its genesis, and thus provides an analogue for detailed interpretations of similar structures encountered during petroleum explorations in the South China Sea or elsewhere.

Multibeam bathymetric, seismic and borehole data are used to investigate a large-scale strike-slip structure, the Baiyun-Liwan Fault Zone, in the northern South China Sea. This fault zone comprises NW- to NE-striking faults and negative flower structures that were generated by oblique extensional displacement. Notably, the interpreted data reveals that the Baiyun-Liwan Fault Zone was active during the Cenozoic, recording intense magmatism, and accommodating significant intraplate deformation during progressive continental rifting and ocean spreading. It bounds two distinct crustal segments and played a significant role in segmenting the northern margin of the South China Sea. The geometry of faults and strata within the Baiyun-Liwan Fault Zone also controlled local sediment routing and depocentre evolution during the Cenozoic. As basement and syn-rift structures change markedly across the Baiyun-Liwan Fault Zone, we propose this structure to be inherited from a lithospheric-scale fault zone separating the Mesozoic arc from forearc-related terrains. We therefore stress the importance of pre-existing structures in the development of rifted margins, with the example provided by the Baiyun-Liwan Fault Zone having profound implications for palaeogeographic reconstructions in the South China Sea. At present, the Baiyun-Liwan Fault Zone is incised by the Pearl River Canyon and eroded by recurrent submarine landslides, forming a major area of sediment bypass towards the abyssal plain.

The origin and evolution of magmatism in rifting margins are a fundamental geological subject, and remain the focus of intense studies. Unlike the classical magma-poor and magma-rich rifting margins, the northern margin of the South China Sea (SCS) exhibits a strong post-rift magmatism, but the evolution and mechanism of this behavior are still poorly understood. In this work we investigate the detailed structural features of the post-rift magmatism in the crust of the SCS northern margin. Our analysis is based on wide-angle and multichannel reflection seismic data, combined with previous seismological results. Our results show a wide distribution of shallow igneous sills and intrusions. These features are spatially and tectonically linked to the lower crustal high-velocity bodies (HVBs) and submarine volcanism, indicating a causative connection between the three features. Considering the existence of an obvious low-velocity branch of the Hainan plume in the northern SCS and uplift of the lithosphere-asthenosphere boundary, we propose that the HVBs reflect consolidated mafic intrusions which formed the lower crustal reservoirs feeding the overlying igneous sills and intrusions. In the SCS northern margin where abundant extensional and detachment faults can act as magmatic channels, such a dynamic process might cause post-rift volcanism. Our results suggest that the crustal magmatic system of post-rift volcanism has a multilevel upward migration mode, and the HVBs in the lower crust could be the product of post-rift magmatism, further indicating that the SCS northern margin had a magma-poor property at the rifting phase but has undergone a strong magmatic rejuvenation by the subsequent mantle plume.

To examine the distribution pattern and controlling factors of oil and gas accumulation in Baiyun Sag systematically, this study analyzes the key factors controlling hydrocarbon accumulation using a large amount of seismic, drilling and geologic data. It is concluded that the oil and gas accumulation is controlled by the following factors: (1) Massive source rock is the physical basis of the formation of medium and large oil and gas fields. (2) Orderly distribution and accumulation of hydrocarbon is regulated by the differential generation of hydrocarbon and differential hydrocarbon accumulation: spacial differential leads to “inner gas, outer oil” pattern, differential accumulation of hydrocarbon controlled the pattern of “inner gas, outer oil” in the east subsag of Baiyun; the timing differential leads to the “upper gas, lower oil” pattern. (3) Late fault activity, diapirs and inherited structural ridges controlled the favorable migration in the Neogene: the activity of faults and diapirs regulated the trap formation and vertical migration of hydrocarbon; inherited structural ridges controlled the Neogene hydrocarbon accumulation. The result effectively guides the exploration in the Baiyun Sag and surrounding area, and provides experience and evidence for the exploration in deepwater area of Pearl River Mouth Basin and other similar basins. Key words: continental margin of northern South China Sea, Baiyun Sag, massive source rock, differential hydrocarbon generation, differential hydrocarbon accumulation, late faults/diapirs, structural ridge

New high-resolution 3D seismic data image a submarine channel complex in the northern slope of the South China Sea. The channel complex stretches hundreds of kilometers across the slope and flows into the deepsea from the siliciclastic shelf margin, linking neritic environment to the pelagic plain. The evolution of the channel complex developed two sedimentary stages, stage I (19.1-18.5 Ma) and stage II (18.5-17.5 Ma), separated by erosional surfaces. In the first stage, the complex was filled with pure siliciclastic sediments, forming thick-massive sandstone intercalated by thin layers of mudstone. During the stage II, the channel complex was deposited five carbonate-siliciclastic cycles. The unexpected channel-fill carbonate deposits present allochthonous characteristics, suggesting the siliciclastic channel was surprisingly used to transport carbonate sediment from the adjacent neritic carbonate platform. By analyzing the periodical carbonate sedimentary process in the siliciclastic channel complex, we infer that it was related to the in situ carbonate production of the neritic carbonate platform and was most likely to be controlled by the relative sea-level changes. Unlike line-source carbonate slope aprons or small-sized carbonate channels, the large-sized siliciclastic channel complex links directly neritic carbonate platform to deepwater basin and can transport large volumes of neritic carbonates to the pelagic environment in a short period. The new findings help to estimate the contributions of neritic siliciclastic shelf and carbonate platform to deepwater slope more accurately. This study suggests that channel systems are more complex than expected and have significant implications on the conceptual models describing the deepwater sedimentary theory.

Three-dimensional blended data, comprised of amplitude and coherence cubes, are used to analyze the evolution of the Central Canyon System (CCS) since the Late Miocene within the western Qiongdongnan Basin (QDNB), South China Sea. The evolution of the canyon since the late Miocene includes two phases and five stages, with a dramatic change of deepwater sediment bodies from early, predominantly axial channel-levee deposits (CLDs) to late, primarily side mass-transport deposits (MTD). During the first and second stages (approximately 5.3–3.7 Ma), axial CLDs derived from the western slope of the South China Sea dominated the sediment bodies within the canyon. The last three stages (3.7 Ma to Recent) were dominated by side MTD, which originated from the northern slope of the South China Sea. Since the canyon was completely filled at 2.4 Ma, axial CLDs only reactivated in the lower strata of the most southern region of the study area. The time of formation of the CCS (approximately 11.6–8.2 Ma) is almost synchronous with the rise of the Himalayas and the first enhancement of the East Asia monsoon during the middle and late Miocene. The change of deepwater deposits within the canyon, which has varied from CLDs to MTDs since 3.7 Ma, is in phase with the further rapid uplift of the entire Tibetan Plateau and the second enhancement of the East Asia monsoon during the middle Pliocene. This evidence suggests that the formation and filling of the canyon should be controlled by the evolution of the Tibetan Plateau and the East Asia monsoon. Tectonics and the East Asia monsoon controlled the evolution of the CCS by changing erosion rates from the Tibetan Plateau, South China Block, and Indochina Peninsula, and sedimentary rates within the Yinggehai Basin and QDNB.

High-resolution seismic and borehole data were used to investigate the sedimentological characteristics of carbonate accumulations in the Pearl River Mouth Basin (PRMB) of the South China Sea. Based on seismic morphologies and petrologic analysis, three scale types of oligo-mesophotic ICBs were identified to have developed ephemerally in the early Early Miocene. The first ICB type is represented by small ICBs with lateral extension in the kilometer range, characterized by mounded geometry, complex internal architectures and a high-frequency alternation of carbonates and volcaniclastics. The second ICB type has lateral extensions of tens of kilometers and convex-up reflections, featuring obvious vertical thickening compared to the surrounding siliciclastic deposits. The third ICB type consist of extensive platforms with hundreds of kilometers of lateral extension, onlapped by surrounding siliciclastic deposits. The correlation of seismic and well data allows us to reconstruct the evolutionary history of the three types of ICBs in the PRMB: All the ICBs built by large benthic foraminifera and/or coralline algae biota, occurred on or around submarine topographic highs such as volcanic edifices or inherited from basement rises, developed under stable subsidence rates between 120 m/Myr and 180 m/Myr, and extinguished suddenly in the late Early Miocene with an abrupt decrease in the subsidence rate or a change from subsidence to tectonic uplift. It is proposed that post-rift subsidence of the study area controlled the evolution of the ICBs. Except for ICBs, mixed carbonate-siliciclastic deposits are identified in well succession, characterized by two types of mixing, namely, compositional mixing (core-plug scale) and strata mixing (stratigraphic scale). These mixed systems generated high-frequency alternations of carbonate, siliciclastic and/or mixed deposits sequence stratigraphy. This work reveals in detail the typical features of seismic morphologies, lithofacies, internal architectures and evolutionary mechanism of ICBs and mixed systems in the PRMB, and thus has implications for predicting reservoirs in hydrocarbon exploration and understanding carbonate sedimentology in a siliciclastic-dominated passive marginal basin.

A giant submarine creep zone exceeding 800 km2 on the continental slope offshore the Dongsha Islands, South China Sea, is investigated using bathymetric and 3D seismic data tied to borehole information. The submarine creep zone is identified as a wide area of seafloor undulations with ridges and troughs. The troughs form NW- and WNW-trending elongated depressions separating distinct seafloor ridges, which are parallel or sub-parallel to the continental slope. The troughs are 0.8–4.7 km-long and 0.4 to 2.1 km-wide. The ridges have wavelengths of 1–4 km and vertical relief of 10–30 m. Slope strata are characterised by the presence of vertically stacked ridges and troughs at different stratigraphic depths, but remaining relatively stationary in their position. The interpreted ridges and troughs are associated with large-scale submarine creep, and the troughs can be divided into three types based on their different internal characters and formation processes. The large-scale listric faults trending downslope below MTD 1 and horizon T0 may be the potential glide planes for the submarine creep movement. High sedimentation rates, local fault activity and the frequent earthquakes recorded on the margin are considered as the main factors controlling the formation of this giant submarine creep zone. Our results are important to the understanding of sediment instability on continental slopes as: a) the interpreted submarine creep is young, or even active at present, and b) areas of creeping may evolve into large-scale slope instabilities, as recorded by similar large-scale events in the past.

Combining multi-channel seismic reflection and gravity modeling, this study has investigated the crustal structure of the northwestern South China Sea margin. These data constrain a hyper-extended crustal area bounded by basin-bounding faults corresponding to an aborted rift below the Xisha Trough with a subparallel fossil ridge in the adjacent Northwest Sub-basin. The thinnest crust is located in the Xisha Trough, where it is remnant lower crust with a thickness of less than 3 km. Gravity modeling also revealed a hyper-extended crust across the Xisha Trough. The postrift magmatism is well developed and more active in the Xisha Trough and farther southeast than on the northwestern continental margin of the South China Sea; and the magmatic intrusion/extrusion was relatively active during the rifting of Xisha Trough and the Northwest Sub-basin. A narrow continent-ocean transition zone with a width of ∼65 km bounded seaward by a volcanic buried seamount is characterized by crustal thinning, rift depression, low gravity anomaly and the termination of the break-up unconformity seismic reflection. The aborted rift near the continental margin means that there may be no obvious detachment fault like that in the Iberia-Newfoundland type margin. The symmetric rift, extreme hyper-extended continental crust and hotter mantle materials indicate that continental crust underwent stretching phase (pure-shear deformation), thinning phase and breakup followed by onset of seafloor spreading and the mantle-lithosphere may break up before crustal-necking in the northwestern South China Sea margin.

Twenty modern submarine channels and buried channels were examined using high-resolution 3D/2D seismic data in the Baiyun Sag, Pearl River Mouth Basin. The channels were dominantly straight, sub-parallel with one another, and oriented perpendicular to the slope contours. Four stages of the deep-water channel system (DCS) were identified according to seismic facies and spatial distribution. The stages were controlled by sediment input and tectonic activities. DCS I is distributed in the middle of the Baiyun Sag, with small individual channels. DCS II expanded because of decreasing sediment input and stable subsidence of the Baiyun Sag increased the slope. DCS III had the broadest distribution and nearly covered the entire Baiyun Sag. Further decreases in sediment input and the Dongsha Event increased the gravity flow domain and greatly promoted the development of the DCS. DCS IV narrowed to the southwest because the buried channels in the northeastern Baiyun Sag ceased after 5.5 Ma as the result of active fault activity. This study highlights that the channel system plays an important role in recording the sedimentary evolution of the Pearl River Mouth Basin and affects the deep-water resource (hydrocarbon and gas hydrate) distribution. (C) 2015 Elsevier Ltd. All rights reserved.

Triple mass-transport deposits (MTDs) with areas of 625, 494 and 902 km2, respectively, have been identified on the north slope of the Xisha Trough, northern South China Sea margin. Based on high-resolution seismic reflection data and multi-beam bathymetric data, the Quaternary MTDs are characterized by typical geometric shapes and internal structures. Results of slope analysis showed that they are developed in a steep slope ranging from 5° to 35°. The head wall scarps of the MTDs arrived to 50 km in length (from headwall to termination). Their inner structures include well developed basal shear surface, growth faults, stepping lateral scarps, erosion grooves, and frontal thrust deformation. From seismic images, the central deepwater channel system of the Xisha Trough has been filled by interbedded channel-levee deposits and thick MTDs. Therefore, we inferred that the MTDs in the deepwater channel system could be dominated by far-travelled slope failure deposits even though there are local collapses of the trough walls. And then, we drew the two-dimensional process model and threedimensional structure model diagram of the MTDs. Combined with the regional geological setting and previous studies, we discussed the trigger mechanisms of the triple MTDs.

The northern margin of the South China Sea (SCS) has particular structural and stratigraphic characteristics that are somewhat different from those described in typical passive margin models. The differences are attributable to poly-phase tectonic movements and magmatic activity resulting from the interaction among the Eurasian, Philippine Sea and Indo-Australian plates. Based on several crustal-scale multi-channel seismic reflection profiles and satellite gravity data across the northetn SCS margin, this paper analyzes the structures, volcanoes and deep crust of the continent-ocean transition zone (COT) at the mid-northern margin of the SCS to study the patterns and model of extension there.

The South China Sea where water depth is up to 5000 m is the most promising oil and gas exploration area in China in the future. The seismic data acquired in the South China Sea contain various types of multiples that need to be removed before imaging can be developed. However, compared with the conventional reflection migration, multiples carry more information of the underground structure that helps provide better subsurface imaging. This paper presents a method to modify the conventional reverse time migration so that multiple reflections can migrate to their correct locations in the subsurface. This approach replaces the numerical impulsive source with the recorded data including primaries and multiples on the surface, and replaces the recorded primary reflection data with multiples. In the reverse time migration process, multiples recorded on the surface are extrapolated backward in time to each depth level, while primaries and multiples recorded on the surface are extrapolated forward in time to the same depth levels. By matching the difference between the primary and multiple images using an objective function, this algorithm improves the primary resultant image. Synthetic tests on Sigsbee2B show that the proposed method can obtain a greater range and better underground illumination. Images of deep water in the South China Sea are obtained using multiples and their matching with primaries. They demonstrate that multiples can make up for the reflection illumination and the migration of multiples is an important research direction in the future.

A large submarine slope failure, the Baiyun Slide Complex, has been discovered in the northern South China Sea. We describe the slide complex morphology, the seismic character of its structural elements and the slide evolution based on high-quality seismic reflection and multi-beam bathymetry data. The Baiyun Slide Complex has three major slide scars that show differences in headwall and sidewall geometry, the nature of the basal shear surfaces and the internal architecture of the deposits. From these observations, we propose a four-phase emplacement model. An extrapolation of the post-slide drape thickness (60 m) gives a rough age estimate for the mass transport events of 0.3 Ma. Pore pressure models for the unfailed continental slope in the vicinity of the Baiyun Slide are based on porosity measurements at nearby Ocean Drilling Program Site 1146. They show that excess pore pressure in slope sediments is anomalously high at a depth around 93 m, most probably as a consequence of a dramatic increase in sedimentation rates over the past 1.8 Ma. This excess pore pressure is proposed to be the major preconditioning factor for the slide initiation, possibly aided by volcano-tectonic activity and gas hydrate dissociation. The unfailed slope is stable under static conditions. However, a near-field earthquake of Mw 5 would suffice to induce a slope instability at c. 93 m depth.

The origin and migration of natural gas and the accumulation of gas hydrates within the Pearl River Mouth Basin of the northern South China Sea are poorly understood. Based on high-resolution 2D/3D seismic data, three environments of focused fluid flow: gas chimneys, mud diapirs and active faults have been identified. Widespread gas chimneys that act as important conduits for fluid flow are located below bottom simulating reflections and above basal uplifts. The occurrence and evolution of gas chimneys can be divided into a violent eruptive stage and a quiet seepage stage. For most gas chimneys, the strong eruptions are deduced to have happened during the Dongsha Movement in the latest Miocene, which are observed below Pliocene strata and few active faults develop above the top of the Miocene. The formation pressures of the Baiyun Sag currently are considered to be normal, based on these terms: 1) Borehole pressure tests with pressure coefficients of 1.043–1.047; 2) The distribution of gas chimneys is limited to strata older than the Pliocene; 3) Disseminated methane hydrates, rather than fractured hydrates, are found in the hydrate samples; 4) The gas hydrate is mainly charged with biogenic gas rather than thermogenic gas based on the chemical tests from gas hydrates cores. However, periods of quiet focused fluid flow also enable the establishment of good conduits for the migration of abundant biogenic gas and lesser volumes of thermogenic gas. A geological model governing fluid flow has been proposed to interpret the release of overpressure, the migration of fluids and the formation of gas hydrates, in an integrated manner. This model suggests that gas chimneys positioned above basal uplifts were caused by the Dongsha Movement at about 5.5 Ma. Biogenic gas occupies the strata above the base of the middle Miocene and migrates slowly into the gas chimney columns. Some of the biogenic gas and small volumes of thermogenic gas eventually contribute to the formation of the gas hydrates.

Because of its potentially important role in the pathogenesis of sepsis, the expression of soluble decoy receptor 3 (DcR3) was investigated in sera of sepsis patients. The serum levels of DcR3 and its tumor necrosis factor-like ligand TL1A and homologous decoy receptor OPG were quantified by ELISA. The values of DcR3 to diagnose sepsis were analyzed by receiver-operating characteristic (ROC) curves. The results showed that DcR3 was significantly elevated in sepsis compared to systemic inflammatory response syndrome (SIRS), a condition similar to sepsis but resulting from noninfectious insults. DcR3 showed superior area under the ROC curve (AUC, 0.958) compared to poor AUCs of TL1A and OPG. At a cut-off of 3.24 ng/mL, DcR3 predicted sepsis from SIRS with 96% sensitivity and 82.6% specificity. DcR3 also predicted sepsis from cancer and inflammatory bowel disease with equally excellent values. Therefore, DcR3 serum level has the potential to serve as a reliable biomarker of sepsis.

Our analysis of approximately 40,000 km of multichannel 2-D seismic data, reef oil-field seismic data, and data from several boreholes led to the identification of two areas of reef carbonate reservoirs in deepwater areas (water depth >= 500 in) of the Qiongdongnan Basin (QDNB), northern South China Sea. High-resolution sequence stratigraphic analysis revealed that the transgressive and highstand system tracts of the mid-Miocene Meishan Formation in the Beijiao and Ledong-Lingshui Depressions developed reef carbonates. The seismic features of the reef carbonates in these two areas include chaotic bedding, intermittent internal reflections, chaotic or blank reflections, mounded reflections, and apparent amplitude anomalies, similar to the seismic characteristics of the LH11-1 reef reservoir in the Dongsha Uplift and Island Reef of the Salawati Basin, Indonesia, which house large oil fields. The impedance values of reefs in the Beijiao and Ledong-Lingshui Depressions are 8000-9000 g/cc x m/s. Impedance sections reveal that the impedance of the LH11-1 reef reservoir in the northern South China Sea is 800010000 g/cc x m/s, whereas that of pure limestone in BD23-1-1 is > 10000 g/cc x m/s. The mid-Miocene paleogeography of the Beijiao Depression was dominated by offshore and neritic environments, with only part of the southern Beijiao uplift emergent at that time. The input of terrigenous sediments was relatively minor in this area, meaning that terrigenous source areas were insignificant in terms of the Beijiao Depression: reef carbonates were probably widely distributed throughout the depression, as with the Ledong-Lingshui Depression. The combined geological and geophysical data indicate that shelf margin atolls were well developed in the Beijiao Depression, as in the Ledong-Lingshui Depression where small-scale patch or pinnacle reefs developed. These reef carbonates are promising reservoirs, representing important targets for deepwater hydrocarbon exploration. (C) 2008 Elsevier Ltd. All rights reserved.

More than 10 gas pools have been discovered since 1983 in the shallow-water region of the Pearl River Mouth (PRM) Basin and the Qiongdongnan (QDN) Basin, offshore South China Sea. Gases produced from the QDN basin are characterized by high contents of benzene and toluene and relatively heavy 13C2 values (25 to 27). The associated condensates have a high abundance of bicadinanes and oleanane, providing a good correlation with the coal-bearing sequence of the Oligocene Yacheng Formation in the basin. In contrast, the gases from the PRM basin contain lower amounts of benzene and toluene and lighter 13C2 values (24 to 34). Widely variable concentrations of bicadinane and oleanane were identifiied from the associated condensates, which can be mostly correlated with the lower Oligocene Enping Formation source rocks formed in a swamp to shallow lake environment. Oil-cracked gases sourced from the Eocene oil-prone source rock may also provide some contribution to the PRM basin gases. The available geochemical data indicate that both the Yacheng and Enping formations contain mainly type III and II2 kerogens with dominant gas potential. Regional geological information indicates that the deep-water regions of the two basins share the same hydrocarbon source sags with the shallow-water areas, and they developed massive sandstone reservoirs during the Oligocene and Miocene. Fluid-flow modeling results show that the deep-water regions were on the pathway of lateral migrating gases, and the interpreted reservoirs in these zones have developed abundant seismic bright spots, which may reflect the presence of gas. The deep-water regions of the offshore South China Sea are believed to have great gas exploration potential.

Natural gas is composed largely of hydrocarbon gas, especially wet gas in the Bozhong sag. The carbon isotopic composition shows that the gas is of organic origin. The carbon isotopic values of ethane indicate that the natural gas is dominated by mixed gas with minor coal-generated gas and oil-type gas. A gas-source correlation study showed that the source rocks of natural gas are those of the Lower Dongying Formation, the Shahejie Formation and the pre-Tertiary. The natural gas is characterized by multi-source and continuous generation in the study area, indicating that gas exploration potential is good in the Bozhong sag.

A large-scale submarine landslide (Baiyun Slide) covering an area of 10,000 km2 was identified from the multibeam bathymetric data, high-resolution 2D and 3D seismic data acquired in the Baiyun Sag, Pearl River Mouth Basin, northern South China Sea (SCS). Numerous polygonal faults are also found below the translational domain of the Baiyun Slide. Enhanced reflections, bright spots and pull-down reflection have been illustrated from the 2D and 3D seismic data, indicating the presence of gas. The headwall scarps of the slide are located stratigraphically above the sediments where the amplitude anomalies are identified. The focused fluid flow maybe leak from the gas reservoir and migrate upward into the base of the Baiyun Slide. Though the triggering mechanism of the Baiyun Slide is still poorly known, the fluid trapped below the slide will reduce the strength of the sediments and trigger the slope failure. We propose a conceptual model of the relationship between fluid migration and slope stability.

The heavy oil, of Fengcheng Oilfield in Xinjiang, is a typical oil which is mainly composed of resin and asphaltene. Because of its high viscosity, density and poor mobility, the heavy oil has to be transferred by pipeline after mixed light oil and heated. This paper states the research on the pipeline transportation technology of heavy oil of Fengcheng Oilfield and proposes six transmission solutions. From the viewpoint of economy, safety and reliability, and by contrast, the optimal solutions of the pipeline material selection, the pipeline design pressure, operating pressure, station distance, the pipeline diameter, in-station temperature and out-station temperature are determined.