Beibu Gulf Basin Research Articles

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

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

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

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

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

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

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

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

Geological Conditions and Suitability Evaluation for CO2 Geological Storage in Deep Saline Aquifers of the Beibu Gulf Basin (South China)

The geological storage of carbon dioxide (CO2) is the most suitable option to achieve a large-scale and low-cost CO2 emissions worldwide, but the selection of favorable areas for the geological storage is the main issue. In this study, evaluation indicators were selected considering four aspects, namely geological conditions, storage potential, hydrogeological conditions, and engineering conditions, based on drilling, geophysical, and geochemical data from the Beibu Gulf Basin. The analytical hierarchy process and the fuzzy comprehensive evaluation method were used to evaluate the suitability of this basin for geological storage of CO2. The results suggested that: (1) the Beibu Gulf Basin is suitable for CO2 geological storage, and the evaluation grade is the highest rating level; (2) considering the techno-economic feasibility, it is necessary to select the target area for CO2 geological storage with suitable burial depth, superior reservoir conditions, proximity to the CO2 collection device, and a high degree of exploration.

CO2 storage potential assessment of offshore saline aquifers in China

Saline Aquifer CO2 Storage (SACS) has become a vitally important technology for mitigating climate change brought on by anthropogenic and fossil fuel emissions. Application of SACS projects in offshore saline aquifers in China is quite promising, and the CO2 storage technical and economic potential are considerable. However, the storage capacities achieved from different analytical and numerical methods varies a lot from each other since the main factors taken into account are variable.In this paper, different methodologies are applied to conduct the assessment of CO2 storage capacity of offshore saline aquifers including Bohai Bay Basin in northern China, also Beibu Gulf Basin and Yinggehai Basin in southern China. Results show that the storage capacity obtained from European Commission’s method is much less than that determined by the other three methods (i.e., USDOE, CSLF and CO2BLOCK method) since it mainly effected by the area of the saline aquifers. Since both of the CSLF and CO2BLOCK methods take into the account the storage mechanisms such as geological structure storage, residual gas storage and dissolution storage, the results seem more reasonable. In addition, the CO2BLOCK method considers the formation stability during injection as well, which is more in accordance with the reality. In summary, the CO2 storage potential of Bohai Bay Basin, Beibu Gulf Basin, and Yinggehai Basin are 39.98, 53.22, and 13.37 Gt, respectively. This further verifies the great potential of industrial-scale pilot and demonstration CO2 storage projects in offshore deep saline aquifers in China.

Assessing a potential site for offshore CO2 storage in the Weixinan Sag in the northwestern Beibu Gulf Basin, northern South China Sea

AbstractGeologic carbon storage (GCS) activities, especially offshore, are still far insufficient worldwide. Sedimentary basins in the northern South China Sea (nSCS) are identified to be favorable to offshore GCS deployment. This study investigates by numerical reservoir simulations the performance of the Weixinan Sag in the northern depression of the Beibu Gulf Basin (BGB), which is considered the most promising area for CO2 offshore GCS in saline formations. Simulations of CO2 injection at a potential site with a normal fault indicate that the pressure buildup induced by CO2 horizontal injection could penetrate extremely low‐permeability faults or caprock formations. The CO2 plumes under higher injection pressures are more constrained in the horizontal direction and hence appear thicker while CO2 tends to spread out horizontally in conditions of low pressure. The impermeable fault renders the CO2 plume about 200 m smaller in size horizontally. Assuming the presence of a fault with a highly permeable core causes leakage to occur after about 30 years of injection, which accounts for only 0.04% the injected amount. For the vertical‐well injection case, the potential CO2 leakage only accounts for around 0.28% of the injection amount, which is far less than the criterion (i.e., 2%) required to make GCS worthwhile. The storage capacities of the formations are mainly controlled by the depths and thicknesses since both their porosities and permeabilities are comparable. The formation Jiaowei‐2 and Xiayang have the largest and second largest storage capacities, respectively, when using a fully perforated well for vertical injection. The average storage capacity of the studied site is 13.04 kg m−3, which is comparable to that of the formation Xiayang. Average injectivities of formations Jiaowei‐2, Xiayang, Weizhou‐1, and Weizhou‐3 are 8.29 × 10−5, 1.75 × 10−4, 6.58 × 10−5, and 2.99 × 10−3 kg s−1 Pa−1, respectively. © 2022 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.

Spatial-temporal evolution of the source-to-sink system in the northwestern South China Sea from the Eocene to the Miocene

The northwestern South China Sea (NW-SCS) presents a spatial-temporal evolution of its source-to-sink (S2S) system, that recorded the movement of the Indochina block and the collision between the Indian and Eurasian plates. However, complex tectonic movements and topographic evolution have led to controversial studies about the spatial-temporal distribution of allogenic materials and autogenic sediments. In this study, we integrated a number of multiscale data to review the S2S system evolution of the northwestern area of the South China Sea from the Eocene to the Miocene. The series include the initial synrift, postrift and thermal subsidence stages. First, we identified the major sediment pathways using seismic profile interpretation. We reconstructed the sediment distribution and lithofacies association within the dispersal sink area based on seismic data, core samples and grain-size analysis. We quantitatively studied the sediment flux and catchment area based on mass balance calculation modeling. Following this, we acquired rare-earth element (REE) data and zircon U–Pb age data from the bedrocks of the continental blocks and the South China Sea Cenozoic basement and rivers in the NW-SCS area to restore the provenance area and evaluate the migration distance by inspecting the heavy mineral assemblages. According to the above studies, three phases of S2S dynamics were identified. 1) The initial rifting stage occurred during the Eocene, and active rifting in the South China Sea induced a major topographic change. A large amount of autogenic slump sediments and a smaller amount of paleo-Red River sediments were injected into the Beibu Gulf Basin (BBGB) and the Yinggehai-Song Hong Basin (YGHB). 2) The postrift stage occurred during the Oligocene. Regional uplift and tectonic inversion probably linked to the clockwise rotation of the Indochina Block, broke the connection between the Beibu Gulf Basin and the Red River catchments. The paleo-Qin River and the paleo-Lian (Nanliu) River brought a large amount of clastic material into the Beibu Gulf Basin from the Cathaysia Block. 3) The thermal subsidence stage occurred during the Miocene: the eastward topographic tilt was enhanced, and the drainage basin entered postrift stage. The development of the Paleo-Red River and its branches, the Lam River and the Ma River, brought distal sediment into the YGHB, while the rivers in the west Cathaysia Block transported sediment into the BBGB. Statistical analysis of the S2S system parameters suggests that the average terrain altitude played a dominant role in determining the S2S system volume during the Eocene, while the dominant role transferred to the sediment supply during the Oligocene and Miocene. • Reconstructs the Source to sink system within NW-SCS from the Eocene to the Miocene. • Reveal the drainage evolution of basins in NW-SCS with multiple dates. • Put out the impact factors to the Source-to-Sink system developed during the rifting process.

The Geochemical Study of Oil-Oil and Oil-Source Rock Correlations in the Wushi Sag of the Beibu Gulf Basin, South China Sea

Chemometrics has been widely used to cope with the problems of oil-oil and oil-source correlations because of its unique advantages in the comprehensive consideration of multiple parameters and the classification of samples or variables. In this paper, three chemometric methods, especially multidimensional scaling, were used to revisit the genetic oil family and the relationship between the crude oil and the source rock, because the oil source in the Wushi Sag, a significant petroliferous sag in the Beibu Gulf Basin of South China Sea, is still controversial. Two genetic families of crude oils, namely group A and group B, have been identified based on chemometric results. Group A oils are characterized by relatively higher Pr/Ph ratios and a high abundance of C27 ααα 20R steranes and C30-methylsteranes than those of group B oils, suggesting that this group of oils was deposited under a more oxic condition with more contribution of algae organic matter. Group A oils have been interpreted to be a mixture derived from the member 2 and member 3 of the Liushagang Formation (LS-2 and LS-3), whereas group B oils can be ascribed to the LS-2 member. The contribution of LS-3 mudstone member to the Wushi oils in previous studies may have been underestimated to some extent, which was inferred from the chemometric oil-source correlation results. The results of oil-source rock correlation may be used to guide future petroleum exploration activities with the incorporation of geological evidence. The spatial distribution of oil and gas reservoirs varies with burial depth. Taking into consideration other geological evidence, we may infer that the reservoir in eastern Wushi Sag was mainly distributed in the deep of Liushagang Formation, whereas the reservoir in southeast Wushi Sag was likely located in the shallow Liushagang Formation.

A new predrilling reservoir permeability prediction model and its application

The accurate prediction of sandstone permeability from variables such as porosity, composition, and texture is one of the major problems in petroleum geology. However, the application of geological variables related to diagenesis in permeability prediction models is relatively rare, especially the anomalous variations of clay content and type. This study investigates the differential control of sedimentation and diagenesis on permeability using a comprehensive analysis of cores, thin sections, routine core analysis, X-ray diffraction, and scanning electron microscopy from sandstone samples in the third member of the Weizhou Formation (Ew3), Weizhou 12-X oilfield, Weixinan Sag, Beibu Gulf Basin, China. An innovative sandstone reservoir permeability prediction model is proposed by introducing the clay factor β confining the effect of clay minerals on permeability, predicting the spatial distribution of diagenetic index (ID) using the Diagenetic Modeling System (DMS), and improving the Walderhaug permeability prediction model. The permeability of the well evaluated in the study was predicted with the relative and absolute errors changing from 0.01 mD to 192.65 mD and from 0.00 to 1.00, with an average values of 38.6 mD and 0.33, respectively, based on the sandstone reservoir permeability prediction model in Ew3. The permeability predicted by the permeability prediction model matches well with the measured permeability in Ew3. The results indicate that permeability is successfully predicted by the modified Walderhaug permeability prediction model for most sandstone reservoirs with strong diagenesis (such as anomalous changes in clay mineral types and content) under the background of a single distributary channel sedimentary microfacies. In general, anomalously high permeability zones are preferentially distributed in dominant sedimentary-diagenetic facies.

Factors controlling organic-rich shale development in the Liushagang Formation, Weixinan Sag, Beibu Gulf Basin: Implications of structural activity and the depositional environment

The mechanisms of lacustrine organic-rich shale formation have attracted attention due to its association with global shale oil and shale gas exploration. Samples of general-quality and excellent-quality source rocks, and oil shale from the Beibu Gulf Basin were analyzed to investigate their organic geochemistry, palynofacies, and trace elements. Hydrocarbon potential was higher in the oil shale (29.79 mg/g) than in the general-quality source rock (3.82 mg/g), and its kerogen type was I-II 2 . Hydrogen-rich liptinite (cutinite and sporinite) components derived from terrigenous higher plants provided most of the hydrocarbon potential of excellent-quality source rock and oil shale. Under the influence of depression-controlling fault activity, a deeper subsidence center promotes the deposition of excellent-quality source rock and oil shale in brackish-hypoxic bottom water. A shallower subsidence center, due to subsag-controlling fault activity, promotes the formation of excellent-quality source rock under fresh-brackish and weak oxidation-weak reducing conditions. The local uplift and shallow-slope led to the formation of general-quality source rock, under freshwater weak-oxidation conditions. A model was established for organic matter (OM) accumulation in organic-rich shales, accounting for fault activity, terrigenous hydrogen-rich OM, and the preservation conditions, to predict the development of excellent-quality source rock from areas with low levels of exploration.

Distribution and origin of anomalously high permeability zones in Weizhou formation, Weizhou 12-X oilfield, Weixinan Sag, China

In order to study the dominant seepage channel of the third member of Weizhou formation (Ew3) in Weizhou 12-X oilfield, Weixinan Sag, Beibu Gulf Basin, and tap the potential of remaining oil. The distribution and causes of the anomalously high permeability zones in Weizhou Formation were studied by using conventional core physical property analysis, scanning electron microscope, laser particle size analysis, X-ray diffraction and thin section microscopic identification. As the results show, vertically,there are three anomalously high permeability zones in the A11, A12 and A21 micro-stage of the middle diagenetic stage, with the depth range of 2300 m ~ 2400 m, 2400 m ~ 2600 m, 2600 m ~ 2900 m respectively. Grain size, sorting, dissolution and early emplacement of hydrocarbons are the main causes of anomalously high permeability zones. Although both grain size and sorting affect porosity and permeability, the effect of grain size on permeability is stronger than sorting, and sorting has a stronger effect on porosity than grain size. Magmatic hydrothermal and organic acid promote dissolution and concomitant porosity and permeability increase by dissolving unstable minerals. The early emplacement of hydrocarbons retard the cementation and accompanying porosity and permeability reduction by reducing the water-rock ratio. Finally, sandstone reservoirs in the Ew3 are characterized by anomalously high permeability zones.

Offshore Petroleum Exploration History and Enlightenment in Beibu Gulf Basin

Offshore Petroleum Exploration History and Enlightenment in Beibu Gulf Basin

Cenozoic structure and tectonics of North subbasins in Beibu Gulf Basin, northern South China Sea

The spatial and temporal interaction of rifting at the northern South China Sea (SCS) margin and shearing along Red River Fault Zone (RRFZ) is crucial to understanding the regional geodynamics. Their obscure relationship has led to controversial models for the origin of the Beibu Gulf basin within the northeast edge of the SCS. Newly released seismic-reflection data and well logs permit a new comprehensive analysis of the tectono-sedimentary history, which provides important constraints on the basin-forming history. Based on the interpretation of 3D multi-channel seismic data, we analyzed the seismic stratigraphy, fault development and tectonic subsidence, with additional confirmation from analogue modelling. The results suggest that several key unconformities separate the rifting history of North subbasins into three distinct phases. The syn-depositional faults and depocenters experienced a tectonic transition from NE- to NNE-orientated during the first two stages. The extensional structures were overprinted by the conjugate strike-slip faulting during stage III (30–23 Ma), as evidenced by the NEE-trending predominant faults and reactivation of NW-trending blind faults. Together with other regional geologic records and plate reconstruction history, we propose an updated view of the region's tectonic history. The NE-trending rift system initiated at the beginning of the Cenozoic. Tectonic reconfiguration at ~40 Ma induced a regional change of stress field to become north-south stretching that caused a tectonic transition of the basin. Influenced by the regional shearing activity of the RRFZ as well as additional north-south stretching, the basin was reworked by widespread strike-slip deformation. We therefore emphasize that while the basin's overall architecture was defined by the development of NE-trending rifts, both reconfiguration of the stress field acting on pre-existing faults and strike-slip reactivation of blind faults led to the basin's current intricate structure.

Crustal Footprint of Mantle Upwelling and Plate Amalgamation Revealed by Ambient Noise Tomography in Northern Vietnam and the Northern South China Sea

AbstractA high‐resolution crustal and uppermost mantle velocity model of northern Vietnam and the northern South China Sea (SCS) is essential for understanding the evolution of the SCS and its relationship to the Hainan plume, which is still controversial. Based on ambient seismic noise analysis, we processed ambient noise data from 65 broadband stations in southwestern China and northern Vietnam to obtain the crustal and uppermost mantle, S‐wave velocity model, through the direct surface‐wave tomography method, with a lateral resolution of 100–150 km. Our results show distinct lateral velocity variation at shallow crustal depths, such as significant low velocity in the Beibu Gulf Basin and the Yinggehai Basin and relatively higher velocity in Hainan Island. We suggest that the low velocity of the lower crust and uppermost mantle beneath the Yinggehai Basin indicates the present upwelling of upper mantle material. However, the observed high‐velocity upheaval feature beneath the Leizhou Peninsula may represent the ancient magmatic underplating, which has a relation to the Hainan plume. Moreover, our results demonstrate different crustal structures of the two flanks of the Red River Fault, that is, in the middle and lower crust, the S‐wave velocity in the region north of the Red River Fault is higher than that in the south. This may be associated with the collision and amalgamation of the South China and Indochina Blocks. In addition, our results also indicate a crustal footprint of the amalgamation of the Yangtze and Cathaysia Blocks.

A quantitative study on source rocks in the western Leidong depression, northern South China Sea

The Leidong depression is one of the secondary tectonic units and the least explored part of the Beibu Gulf Basin, northern South China Sea. Exploration activities in the basin reveal that the Middle Eocene deposition was controlled by NE-SW-striking faults and the second member of the Eocene Liushagang Formation (LⅡ) consists of high-quality source rocks. The nature and origin of this depression has remained enigmatic due to the complex fault structures as compared to those in other basins. It is important to identify whether LⅡ occurs in the Leidong depression in the context of exploration. Here we analyze available geological, seismic, and drilling data of the depression and the controlling factors among faults, deposition, lithology, and hydrocarbon distribution in the basin. Measures such as stress fracture analysis, fault growth index analysis, and sedimentary strata characterization were used to construct an Eocene sedimentary model controlled by NW-SE striking faults. The model with integrated seismic profile characteristics comparison and velocity analysis results was then used to determine whether the Eocene strata in the west of the depression contain the high-quality source rocks that are widely distributed elsewhere in the basin. Finally, calculations were performed to quantify the intensity of hydrocarbon generation and amount of hydrocarbon generated in the depression based on available data of the source rocks, including their distribution and thickness. The results confirmed the assumption that the Middle Eocene strata in the Leidong depression were controlled by NW-SE strike-slip faults and contain high-quality LⅡ source rocks, thus providing an important foundation for future exploration.

Petroleum Origins and Accumulation Patterns in the Weixinan Sag in the Beibu Gulf Basin, Using Subsag B as an Example

AbstractCrude oil has been discovered in the Paleogene and Neogene units of the Weixinan Sag in the Beibu Gulf Basin. To determine the source and accumulation mode of this crude oil, 12 crude oil samples and 27 source rock samples were collected and an extensive organic geochemical analysis was conducted on them. Based on the geological conditions and the analytical results, the types, origins and accumulation patterns of crude oil in the study area were elucidated. Except for a shallowly‐buried and biodegraded crude oil deposit in Neogene rocks, the crude oil samples in the study area were normal. All of the crude oils were derived from lacustrine source rocks. According to biomarker compositions, the crude oils could be divided into two families, A and B, distinctions that were reinforced by differences in carbon isotope composition and spatial distribution. Oil‐source correlation analysis based on biomarkers revealed that Family A oils were derived from the mature oil shale at the bottom of the second member of the Liushagang Formation, while the Family B oils formed in the mature shale of the Liushagang Formation. The Family A oils, generated by oil shale, mainly migrated laterally along sand bodies and were then redistributed in adjacent reservoirs above and below the oil shale layer, as well as in shallow layers at high structural positions, occupying a wide distribution range. The Family B oils were generated by other shale units before migrating vertically along faults to form reservoirs nearby, resulting in a narrow distribution range.

Plate tectonic control on the formation and tectonic migration of Cenozoic basins in northern margin of the South China Sea

The tectonic evolution history of the South China Sea (SCS) is important for understanding the interaction between the Pacific Tectonic Domain and the Tethyan Tectonic Domain, as well as the regional tectonics and geodynamics during the multi-plate convergence in the Cenozoic. Several Cenozoic basins formed in the northern margin of the SCS, which preserve the sedimentary tectonic records of the opening of the SCS. Due to the spatial non-uniformity among different basins, a systematic study on the various basins in the northern margin of the SCS constituting the Northern Cenozoic Basin Group (NCBG) is essential. Here we present results from a detailed evaluation of the spatial-temporal migration of the boundary faults and primary unconformities to unravel the mechanism of formation of the NCBG. The NCBG is composed of the Beibu Gulf Basin (BBGB), Qiongdongnan Basin (QDNB), Pearl River Mouth Basin (PRMB) and Taixinan Basin (TXNB). Based on seismic profiles and gravity-magnetic anomalies, we confirm that the NE-striking onshore boundary faults propagated into the northern margin of the SCS. Combining the fault slip rate, fault combination and a comparison of the unconformities in different basins, we identify NE-striking rift composed of two-stage rifting events in the NCBG: an early-stage rifting (from the Paleocene to the Early Oligocene) and a late-stage rifting (from the Late Eocene to the beginning of the Miocene). Spatially only the late-stage faults occurs in the western part of the NCBG (the BBGB, the QDNB and the western PRMB), but the early-stage rifting is distributed in the whole NCBG. Temporally, the early-stage rifting can be subdivided into three phases which show an eastward migration, resulting in the same trend of the primary unconformities and peak faulting within the NCBG. The late-stage rifting is subdivided into two phases, which took place simultaneously in different basins. The first and second phase of the early-stage rifting is related to back-arc extension of the Pacific subduction retreat system. The third phase of the early-stage rifting resulted from the joint effect of slab-pull force due to southward subduction of the proto-SCS and the back-arc extension of the Pacific subduction retreat system. In addition, the first phase of the late-stage faulting corresponds with the combined effect of the post-collision extension along the Red River Fault and slab-pull force of the proto-SCS subduction. The second phase of the late-stage faulting fits well with the sinistral faulting of the Red River Fault in response to the Indochina Block escape tectonics and the slab-pull force of the proto-SCS.

Total organic carbon content prediction based on support-vector-regression machine with particle swarm optimization

Total organic carbon (TOC) is a significant factor to evaluate the hydrocarbon potential of the unconventional reservoir, while it is difficult to obtain the continuous and accurate prediction result of TOC by traditional methods due to the non-linear relationship between TOC content and wireline log data. However, support vector regress machine is an efficient supervised learning artificial intelligence algorithm, and performs well to deal with non-linear relationship dataset. Therefore, in order to explore a more efficient way for TOC content prediction, the support vector regress machine was tried to predict TOC content through wireline log data. To further verify this, some data tests have been conducted on an offshore exploration prior well data in the northern of Beibu Gulf Basin. After analyzing various kernel functions and optimization methods by cross-validation and error analysis, it can be indicated that the Gaussian kernel function and the particle swarm optimization (PSO) algorithm which used the linear decreasing inertia coefficient and mutated particles are suitable for SVR model and model parameter selection, respectively. Finally, the prediction result of SVR with the best model and model parameters is compared with the results of an improved ΔlogR method and multilayer perceptron method. The comparison results show that SVR has a higher correlation coefficient than other methods. In conclusion, the prediction result of SVR can be thought of as an efficient and reliable method for TOC content prediction. Through the continuous prediction of organic carbon content, the qualitative and quantitative evaluation of high-quality source rocks in this area can be realized, which is of great practical significance for determining the exploration field and the search for favorable target reservoirs.

Automatic Extraction of Offshore Platforms in Single SAR Images Based on a Dual-Step-Modified Model.

The quantity and location of offshore platforms are of great significance for marine oil spill monitoring and offshore oil-gas development. In the past, multiphase medium- and low-resolution optical or radar images have been used to remove the interference of ship targets based on the static position of a platform to extract the offshore platform, resulting in large demands and high image data costs. According to the difference in shape between offshore platforms (not elongated) and ships (elongated shapes) in SAR (synthetic aperture radar) images, this paper proposes an automatic extraction method for offshore platforms in single SAR images based on a dual-step-modified model. First, the two-parameter CFAR (constant false alarm rate) algorithm was used to detect the possible offshore platform targets; then, the Hough transform was introduced to detect and eliminate ship targets with linear structures. Finally, the final offshore platform was obtained. Experiments were carried out in four study areas in the Beibu Gulf basin and the Pearl River estuary basin in the northern South China Sea. The results show that the method has a good extraction effect in the above research area, and the extraction accuracy rate of offshore platforms is 86.75%. A single SAR image can obtain satisfactory extraction results, which greatly saves on image data cost.