Bottom acoustic parameters play an important role in sound field prediction. Acoustic parameters in deep water are not well understood. Bottom acoustic parameters are sensitive to the transmission-loss (TL) data in ...Bottom acoustic parameters play an important role in sound field prediction. Acoustic parameters in deep water are not well understood. Bottom acoustic parameters are sensitive to the transmission-loss (TL) data in the shadow zone of deep water. We propose a multiple-step fill inversion method to invert sound speed, density and attenuation in deep water. Based on a uniform liquid hMf-space bottom model, sound speed of the bottom is inverted by using the long range TL at low frequency obtained in an acoustic propagation experiment conducted in the South China Sea (SCS) in summer 2014. Meanwhile, bottom density is estimated combining with the Hamilton sediment empirical relationship. Attenuation coefficients at different frequencies are then estimated from the TL data in the shadow zones by using the known sound speed and density as a constraint condition. The nonlinear relationship between attenuation coefficient and frequency is given in the end. Tile inverted bottom parameters can be used to forecast the transmission loss in the deep water area of SCS very we//.展开更多
BSR (Bottom Simulating Reflector) occurs widely in the strata since the late Miocene in the deep-water area of the northern continental slope of South China Sea (SCS). It is an important seismic reference mark whi...BSR (Bottom Simulating Reflector) occurs widely in the strata since the late Miocene in the deep-water area of the northern continental slope of South China Sea (SCS). It is an important seismic reference mark which identifies the gas hydrate and its distribution influenced by the tectonic movements. Single-point basin modeling was conducted using 473 points in the study area. To discuss the relationships between the tectonic subsidence and BSR, the volume and rate of tectonic subsidence in each geological time have been simulated. The results show that there are three tectonic accelerate subsidence processes in the study area since the late Miocene, especially since 1.8Ma the tectonic subsidence accelerates more apparently. Since the Late Miocene to Pleistocene, the rate of tectonic subsidence in deep-water underwent a transformation from weak to strong. The ratio of tectonic subsidence to the total subsidence was relatively high (65-70%). Through the superposition of the BSR developed areas and the contours of tectonic subsidence in this area, it was discovered that more than 80% of BSR tend to be distributed at the slope break or depression-uplift structural transfer zone and the average tectonic subsidence rate ranges from 70 m/Ma to 125 m/Ma.展开更多
The deep-water area of the northern South China Sea, which has active and complicated tectonics, is rich in natural gas and gas hydrate. While the tectonic characteristics is different obviously between the east and t...The deep-water area of the northern South China Sea, which has active and complicated tectonics, is rich in natural gas and gas hydrate. While the tectonic characteristics is different obviously between the east and the west because of the special tectonic position and tectonic evolution process. In terms of submarine geomorphology, the eastern shelf-slope structure in Pearl River Mouth Basin is characterized by having wide sub-basins and narrow intervening highs, whereas the western (Qiongdongnan Basin) structure is characterized by narrow sub- basins and wide uplift. As to the structural features, the deep-water sags in the east are all structurally half- grabens, controlled by a series of south-dipping normal faults. While the west sags are mainly characterised by graben structures with faulting in both the south and north. With regards to the tectonic evolution, the east began neotectonic activity when the post-rifting stage had completed at the end of the Middle Miocene. In the Baiyun Sag, tectonic activity became strong and was characterised by rapid subsidence and obvious faulting. Whereas in the west, neotectonic activity began at the end of the Late Miocene with rapid deposition and weak fault activity.展开更多
The internal seismic architectures of the Middle Miocene in Beikang Basin, southern South China Sea, were investigated and described using regional 2D seismic data from Guangzhou Marine Geology Survey. In particular, ...The internal seismic architectures of the Middle Miocene in Beikang Basin, southern South China Sea, were investigated and described using regional 2D seismic data from Guangzhou Marine Geology Survey. In particular, five typical seismic facies were identified based on an integrated analysis of the amplitude, continuity, contact relationship, and morphologies of seismic reflections. Bathyal-abyssal fine-grained sediments, deltaic front sandy bodies, turbidites, and small-scale turbidite channels were developed in the Middle Miocene according to the tectonic-sedimentary evolution of the sedimentary basins in the southern South China Sea. The findings of this study suggest that deltaic front sandy bodies and turbidites can be considered as the two major types of deep-water clastic reservoirs for the depression stage of Beikang Basin. A well-developed source-reservoir-cap assemblage was composed by deep rift-stage source rocks, deep-water clastic reservoirs of the Middle Miocene, and bathyal-abyssal deep-water fine-grained sediments after the Middle Miocene, implying a good potential for hydrocarbon exploration.展开更多
The relationships between crustal stretching and thinning,basin structure and petroleum geology in Baiyun deep-water area were analyzed using large area 3D seismic,gravity,magnetic,ocean bottom seismic(OBS),deep-water...The relationships between crustal stretching and thinning,basin structure and petroleum geology in Baiyun deep-water area were analyzed using large area 3D seismic,gravity,magnetic,ocean bottom seismic(OBS),deep-water exploration wells and integrated ocean drilling program(IODP).During the early syn-rifting period,deep-water area was a half-graben controlled by high angle faults influenced by the brittle extension of upper crust.In the mid syn-rifting period,this area was a broad-deep fault depression controlled by detachment faults undergone brittle-ductile deformation and differentiated extension in the crust.In the late syn-rifting period,this area experienced fault-sag transition due to saucer-shaped rheology change dominated by crustal ductile deformation.A broad-deep fault depression controlled by the large detachment faults penetrating through the crust is an important feature of deep-water basin.The study suggests that the broad-deep Baiyun sag provides great accommodation space for the development of massive deltaic-lacustrine deposition system and hydrocarbon source rocks.The differentiated lithospheric thinning also resulted in the different thermal subsidence during post-rifting period,and then controlled the development of continental shelf break and deep-water reservoir sedimentary environment.The high heat flow background caused by the strong thinning of lithosphere and the rise of mantle source resulted in particularities in the reservoir diagenesis,hydrocarbon generation process and accumulation of deep-water area in northern South China Sea.展开更多
Dongsha waters are poorly studied for gas hydrates. Previous multi-channel seismic reflection and Chirp sub- bottom profiles show that numerous submarine mounds stand up to 100 m high above the seafloor over the conti...Dongsha waters are poorly studied for gas hydrates. Previous multi-channel seismic reflection and Chirp sub- bottom profiles show that numerous submarine mounds stand up to 100 m high above the seafloor over the continental slope of the SW Dongsha Island in northern margin of the South China Sea (SCS). These mounds are characterized by hardened seabed, seafloor gas venting and folded structures, which implies the existence of active mud volcanoes. This work aims to confirm this speculation by seafloor sample dredging and to explore the potential of gas hydrates.展开更多
Great advancement has been made on natural gas hydrates exploration and test production in the northern South China Sea.However,there remains a lot of key questions yet to be resolved,particularly about the mechanisms...Great advancement has been made on natural gas hydrates exploration and test production in the northern South China Sea.However,there remains a lot of key questions yet to be resolved,particularly about the mechanisms and the controls of gas hydrates enrichment.Numerical simulaution would play signficant role in addressing these questions.This study focused on the gas hydrate exploration in the Shenhu Area,Northern South China Sea.Based on the newly obtained borehole and multichannel reflection seismic data,the authors conducted an integrated 3D basin modeling study on gas hydrate.The results indicate that the Shenhu Area has favorable conditions for gas hydrate accumulation,such as temperature,pressure,hydrocarbon source,and tectonic setting.Gas hydrates are most concentrated in the Late Miocene strata,particularly in the structual highs between the Baiyun Sag and the Liwan Sag,and area to the south of it.It also proved the existence of overpressure in the main sag of source rocks,which was subject to compaction disequilibrium and hydrocarbon generation.It also shown that the regional fault activity is not conducive to gas hydrate accumulation due to excess gas seepage.The authors conjecture that fault activity may slightly weaken overpressure for the positive effect of hydrocarbon expulsion and areas lacking regional fault activity have better potential.展开更多
More than 4 000 km 48-channel seismic reflection data from the central region of the South China Sea have been interpreted. Five seismic interfaces have been distinguished, named T1, T2, T4, T6 and Tg respectively Mea...More than 4 000 km 48-channel seismic reflection data from the central region of the South China Sea have been interpreted. Five seismic interfaces have been distinguished, named T1, T2, T4, T6 and Tg respectively Meanwhile, five seismic sequences numbered I - V have been divided with the ages of Quaternary and Pliocene, Later Mocene, Earlier and Middle Miocene, Oligocene and Pre- Oligocene separately. Sequences I-II overlie all parts of the area. In the continental slope and island slope, Sequences III-V are mainly found in the grabens. Sequence III is found at moot profiles of the deep-sea basin, and Sequnce IV is seen not only at the margins of the east subbasin but also at the margins of the southwest subbasin. Strong reflection from Moho is found at most profiles of the deep-sea basin. The depth of Moho varies between 10 and 12 km, with a thickness of 6- 8 km for the crust. Calculated by age-basement depth correlation formula, the age of basaltic basement in the southwest subbasin is 51-39 Ma. It is indicated that the evolution of the southwest subbasin is simultaneous with or earlier than that of the east subbasin.展开更多
The deepwater of the northwestern South China Sea is located in the central to southern parts of the Qiongdongnan Basin (QDN Basin), which is a key site for hydrocarbon exploration in recent years. In this study, th...The deepwater of the northwestern South China Sea is located in the central to southern parts of the Qiongdongnan Basin (QDN Basin), which is a key site for hydrocarbon exploration in recent years. In this study, the authors did a comprehensive analysis of gravity-magnetic data, extensive 3D seismic survey, cores and cuttings, paleontology and geochemical indexes, proposed the mechanism of natural gas origin, identified different oil and gas systems, and established the model of hydrocarbon accumulations in the deep-water region. Our basin tectonic simulation indicates that the evolution of QDN Basin was controlled by multiple-phased tectonic movements, such as Indochina-Eurasian Plate collision, Tibetan Uplift, Red River faulting and the expansion of the South China Sea which is characterized by Paleogene rifting, Neogene depression, and Eocene intensive faulting and lacustrine deposits. The drilling results show that this region is dominated by marine- terrestrial transitional and neritic-bathyal facies from the early Oligocene. The Yacheng Formation of the early Oligocene is rich in organic matter and a main gas-source rock. According to the geological-geochemical data from the latest drilling wells, Lingshui, Baodao, Changchang Sags have good hydrocarbon-generating potentials, where two plays from the Paleogene and Neogene reservoirs were developed. Those reservoirs occur in central canyon structural-lithologic trap zone, Changchang marginal trap zone and southern fault terrace of Baodao Sag. Among them, the central canyon trap zone has a great potential for exploration because the various reservoir- forming elements are well developed, i.e., good coal-measure source rocks, sufficient reservoirs from the Neogene turbidity sandstone and submarine fan, faults connecting source rock and reservoirs, effective vertical migration, late stage aggregation and favorable structural-lithological composite trapping. These study results provide an important scientific basis for hydrocarbon exploration in this region, evidenced by the recent discovery of the significant commercial LS-A gas field in the central canyon of the Lingshui Sag.展开更多
The Baiyun Sag, located in the deep-water area of the northern South China Sea, is the largest and deepest subbasin in the Pearl River Mouth Basin and one of the most important hydrocarbon-accumulation depression area...The Baiyun Sag, located in the deep-water area of the northern South China Sea, is the largest and deepest subbasin in the Pearl River Mouth Basin and one of the most important hydrocarbon-accumulation depression areas in China. Thermal history is widely thought to be of great importance in oil and gas potential assessment of a basin as it controls the timing of hydrocarbon generation and expulsion from the source rock. In order to unravel the paleo-heat flow of the Baiyun Sag, we first analyzed tectonic subsidence of 55 pseudo-wells constructed based on newly interpreted seismic profiles, along with three drilled wells. We then carried out thermal modeling using the multi-stage finite stretching method and calibrated the results using collected present-day vitrinite reflectance data and temperature data. Results indicate that the first and second heating of the Baiyun Sag after 49 Ma ceased at 33.9 Ma and 23 Ma. Reconstructed average basal paleo- heat flow values at the end of the rifting periods are -57.7- 86.2 mW/m2 and -66.7-97.3 mW/m2, respectively. Following the last heating period at 23 Ma, the study area has undergone a persistent thermal attenuation phase, and basal heat flow has cooled down to ~64.0-79.2 mW/m2 at present.展开更多
Based on the interpretation of high resolution 2D/3D seismic data, sedimentary filling characteristics and full- filled time of the Central Canyon in different segments in the Qiongdongnan Basin of northwestern South ...Based on the interpretation of high resolution 2D/3D seismic data, sedimentary filling characteristics and full- filled time of the Central Canyon in different segments in the Qiongdongnan Basin of northwestern South China Sea have been studied. The research results indicate that the initial formation age of the Central Canyon is traced back to 11.6 Ma (T40), at which the canyon began to develop due to the scouring of turbidity currents from west to east. During the period of 11.6-8.2 Ma (T40-T31), strong downcutting by gravity flow occurred, which led to the formation of the canyon. The canyon fillings began to form since 8.2 Ma (T31) and were dominated by turbidite deposits, which constituted of lateral migration and vertical superposition of turbidity channels during the time of 8.2-5.5 Ma. The interbeds of turbidity currents deposits and mass transport deposits (MTDs) were developed in the period of 5.5-3.8 Ma (T30-T28). After then, the canyon fillings were primarily made up of large scale MTDs, interrupted by small scale turbidity channels and thin pelagic mudstones. The Central Canyon can be divided into three types according to the main controlling factors, geomorphology-controlled, fault-controlled and intrusion- modified canyons. Among them, the geomorphology-controlled canyon is developed at the Ledong, Lingshui, Songnan and western Baodao Depressions, situated in a confined basin center between the northern slope and the South Uplift Belt along the Central Depression Belt. The fault-controlled canyon is developed mainly along the deep-seated faults in the Changchang Depression and eastern Baodao Depression. Intrusion-modified canyon is only occurred in the Songnan Low Uplift, which is still mainly controlled by geomorphology, the intrusion just modified seabed morphology. The full-filled time of the Central Canyon differs from west to east, displaying a tendency of being successively late eastward. The geomorphology-controlled canyon was completely filled before 3.8 Ma (T28), but that in intrusion-modified canyon was delayed to 2.4 Ma (T27) because of the uplifted southern canyon wall. To the Changchang Depression, the complete filling time was successively late eastward, and the canyon in eastern Changchang Depression is still not fully filled up to today. Difference in full-filled time in the Central Canyon is mainly governed by multiple sediment supplies and regional tectonic activities. Due to sufficient supply of turbidity currents and MTDs from west and north respectively, western segment of the Central Canyon is entirely filled up earlier. Owing to slower sediment supply rate, together with differential subsidence by deep-seated faults, the full-filled time of the canyon is put off eastwards gradually.展开更多
Conductor and suction anchor are the key equipment providing bearing capacity in the field of deep-water drilling or offshore engineering,which have the advantages of high operation efficiency and short construction p...Conductor and suction anchor are the key equipment providing bearing capacity in the field of deep-water drilling or offshore engineering,which have the advantages of high operation efficiency and short construction period.In order to drill a horizontal well in the shallow hydrate reservoir in the deep water,the suction anchor wellhead assembly is employed to undertake the main vertical bearing capacity in the second round of hydrate trial production project,so as to reduce the conductor running depth and heighten the kick-off point position.However,the deformation law of the deep-water suction anchor wellhead assembly under the moving load of the riser is not clear,and it is necessary to understand the lateral bearing characteristics to guide the design of its structural scheme.Based on 3D solid finite element method,the solid finite element model of the suction anchor wellhead assembly is established.In the model,the seabed soil is divided into seven layers,the contact between the wellhead assembly and the soil is simulated,and the vertical load and bending moment are applied to the wellhead node to simulate the riser movement when working in the deep water.The lateral bearing stability of conventional wellhead assembly and suction anchor wellhead assembly under the influence of wellhead load is discussed.The analysis results show that the bending moment is the main factor affecting the lateral deformation of the wellhead string;the anti-bending performance from increasing the outer conductor diameter is better than that from increasing the conductor wall thickness;for the subsea wellhead,the suction anchor obviously improves the lateral bearing capacity and reduces the lateral deformation.The conduct of the suction anchor wellhead assembly still needs to be lowered to a certain depth that below the maximum disturbed depth to ensure the lateral bearing stability,Thus,a method for the minimum conductor running depth for the suction anchor wellhead assembly is developed.The field implementations show that compared with the first round of hydrate trial production project,the conductor running depth is increased by 9.42 m,and there is no risk of wellhead overturning during the trial production.The method for determining the minimum conductor running depth in this paper is feasible and will still play an important role in the subsequent hydrate exploration and development.展开更多
This study elucidates sedimentary evolution history of the Central Canyon System(CCS),a large axial submarine canyon in the Qiongdongnan Basin(QDNB),northern South China Sea.Thegeomorphological characteristics and inf...This study elucidates sedimentary evolution history of the Central Canyon System(CCS),a large axial submarine canyon in the Qiongdongnan Basin(QDNB),northern South China Sea.Thegeomorphological characteristics and infill architectures of the CCS are summarized based on theanalysis of two-and three-dimensional seismic data.Based on a comparative analysis of the CCS indifferent segments and evolutionary stages and in consideration of the tectono-sedimentary conditionsof the QDNB four stages of the sedimentary evolution of the CCS can be divided,i.e.initialdevelopment stage in the Late Miocene(11.6-5.7Ma),erosion-infilling stage in the Early Pliocene(5.7-3.7 Ma),tranquil infilling stage in the Late Pliocene(3.7-1.81 Ma),and rejuvenation stage sincethe Pleistocene(1.81 Ma to present).In the 1ate Middle Miocene(~11.6 Ma),the rudiment of CCswas developed by a regional tectonic transformation in the eastern part of the basin.In the EarlyPliocene,the CCS was further developed from west to east and restrained in the central depressionbelt of the basin due to abundant sediment supplies from the northwestern and northem provenances,the blocking effect of the southern uplift belt,and the restrictive geomorphological features of theeastern part of the basin.In the Late Pliocene,changes in the sedimentary environment resulted in thedevelopment of the CCS in the eastern part of the basin only.Since the Pleistocene,the joint action ofclimatic factors and geomorphological features of the eastern part of the basin led to the rejuvenationof the CCS.展开更多
The tectonic cycle of the marginal sea basins in South China Sea(SCS)includes two cycles,i.e.,the formation and contraction of Palaeo-SCS and Neo-SCS.The northern part of SCS is a rift basin on a passive continental m...The tectonic cycle of the marginal sea basins in South China Sea(SCS)includes two cycles,i.e.,the formation and contraction of Palaeo-SCS and Neo-SCS.The northern part of SCS is a rift basin on a passive continental margin,while the the Nansha Block is a drifting rift basin.The southern part is a compound compressional basin on an active continental margin;the western part is a shear-extensional basin on a transform continental margin;the eastern part is an accretionary wedge basin on a subduction continental margin.The deep-water basins are mainly distributed on the continental slope and the the Nansha Block.There are three sets of source rocks in the deep-water areas of the northern continental margin in SCS,i.e.,Eocene terrestrial facies,early Oligocene transitional facies and late Oligocene marine facies.A set of Late Cretaceous-Early Oligocene terrestrial marine facies source rocks are developed in the drift-rift basin of SCS.Three sets of Oligocene,early Miocene and Mid-Miocene marine-terrestrial transitional facies source rocks are developed in the deep-water areas of both the southern and western continental margins of SCS.Four sets of reservoirs developed in the northern deep waters of SCS are dominated by deep sea fans.Two sets of reservoirs developed in the the Nansha Block are dominated by delta and biogenic reef.The southern part of SCS is dominated by deep sea fan and biogenic reef.Reservoirs of large channels and other clastic facies were developed in front of the estuaries,while biogenic reef bank was formed in the uplift zone.The hydrocarbon accumulation assemblages are mainly presented as Oligocene-Pliocene in the deep waters on the northern continental margin of SCS,Eocene-Lower Oligocene in the the Nansha Block,Oligocene-Pliocene and Oligocene-Miocene in the deep waters on the southern and western continental margin of SCS,respectively.The major hydrocarbon reservoir types in the deep waters of SCS are related to structural traps,deep water fans and biogenic reefs.The formation of basin,hydrocarbon and reservoir in the deep waters of SCS are controlled by the tectonic cycles of the marginal sea basins,revealing a great potential for hydrocarbon exploration.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 11434012,41561144006,11174312 and 11404366
文摘Bottom acoustic parameters play an important role in sound field prediction. Acoustic parameters in deep water are not well understood. Bottom acoustic parameters are sensitive to the transmission-loss (TL) data in the shadow zone of deep water. We propose a multiple-step fill inversion method to invert sound speed, density and attenuation in deep water. Based on a uniform liquid hMf-space bottom model, sound speed of the bottom is inverted by using the long range TL at low frequency obtained in an acoustic propagation experiment conducted in the South China Sea (SCS) in summer 2014. Meanwhile, bottom density is estimated combining with the Hamilton sediment empirical relationship. Attenuation coefficients at different frequencies are then estimated from the TL data in the shadow zones by using the known sound speed and density as a constraint condition. The nonlinear relationship between attenuation coefficient and frequency is given in the end. Tile inverted bottom parameters can be used to forecast the transmission loss in the deep water area of SCS very we//.
基金supported by the National 973 Basic Research Program (Grant No. 2009CB219502)National Natural Science Foundation of China (Grant No. 41072084)
文摘BSR (Bottom Simulating Reflector) occurs widely in the strata since the late Miocene in the deep-water area of the northern continental slope of South China Sea (SCS). It is an important seismic reference mark which identifies the gas hydrate and its distribution influenced by the tectonic movements. Single-point basin modeling was conducted using 473 points in the study area. To discuss the relationships between the tectonic subsidence and BSR, the volume and rate of tectonic subsidence in each geological time have been simulated. The results show that there are three tectonic accelerate subsidence processes in the study area since the late Miocene, especially since 1.8Ma the tectonic subsidence accelerates more apparently. Since the Late Miocene to Pleistocene, the rate of tectonic subsidence in deep-water underwent a transformation from weak to strong. The ratio of tectonic subsidence to the total subsidence was relatively high (65-70%). Through the superposition of the BSR developed areas and the contours of tectonic subsidence in this area, it was discovered that more than 80% of BSR tend to be distributed at the slope break or depression-uplift structural transfer zone and the average tectonic subsidence rate ranges from 70 m/Ma to 125 m/Ma.
基金The National Basic Research Program(973 Program)of China under contract No.2009CB219401Science and Technology Program of Guangzhou under contract No.201505041038084+2 种基金the Open Fund of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Southwest Petroleum University)under contract No.PLN1401the Key Laboratory of Gas Hydrate,Ministry of Land and Resources under contract No.SHW(2014)-DX-01the State Key Laboratory Breeding Base of Nuclear Resources and Environment,East China Institute of Technology under contract No.NRE1302
文摘The deep-water area of the northern South China Sea, which has active and complicated tectonics, is rich in natural gas and gas hydrate. While the tectonic characteristics is different obviously between the east and the west because of the special tectonic position and tectonic evolution process. In terms of submarine geomorphology, the eastern shelf-slope structure in Pearl River Mouth Basin is characterized by having wide sub-basins and narrow intervening highs, whereas the western (Qiongdongnan Basin) structure is characterized by narrow sub- basins and wide uplift. As to the structural features, the deep-water sags in the east are all structurally half- grabens, controlled by a series of south-dipping normal faults. While the west sags are mainly characterised by graben structures with faulting in both the south and north. With regards to the tectonic evolution, the east began neotectonic activity when the post-rifting stage had completed at the end of the Middle Miocene. In the Baiyun Sag, tectonic activity became strong and was characterised by rapid subsidence and obvious faulting. Whereas in the west, neotectonic activity began at the end of the Late Miocene with rapid deposition and weak fault activity.
文摘The internal seismic architectures of the Middle Miocene in Beikang Basin, southern South China Sea, were investigated and described using regional 2D seismic data from Guangzhou Marine Geology Survey. In particular, five typical seismic facies were identified based on an integrated analysis of the amplitude, continuity, contact relationship, and morphologies of seismic reflections. Bathyal-abyssal fine-grained sediments, deltaic front sandy bodies, turbidites, and small-scale turbidite channels were developed in the Middle Miocene according to the tectonic-sedimentary evolution of the sedimentary basins in the southern South China Sea. The findings of this study suggest that deltaic front sandy bodies and turbidites can be considered as the two major types of deep-water clastic reservoirs for the depression stage of Beikang Basin. A well-developed source-reservoir-cap assemblage was composed by deep rift-stage source rocks, deep-water clastic reservoirs of the Middle Miocene, and bathyal-abyssal deep-water fine-grained sediments after the Middle Miocene, implying a good potential for hydrocarbon exploration.
基金Supported by the Science and Technology Project of CNOOC Ltd.(YXKY-2012-SHENHAI-01)China National Science and Technology Major Project(2011ZX05025-003+1 种基金 2016ZX05026-003)the National Natural Science Foundation of China(91128207)
文摘The relationships between crustal stretching and thinning,basin structure and petroleum geology in Baiyun deep-water area were analyzed using large area 3D seismic,gravity,magnetic,ocean bottom seismic(OBS),deep-water exploration wells and integrated ocean drilling program(IODP).During the early syn-rifting period,deep-water area was a half-graben controlled by high angle faults influenced by the brittle extension of upper crust.In the mid syn-rifting period,this area was a broad-deep fault depression controlled by detachment faults undergone brittle-ductile deformation and differentiated extension in the crust.In the late syn-rifting period,this area experienced fault-sag transition due to saucer-shaped rheology change dominated by crustal ductile deformation.A broad-deep fault depression controlled by the large detachment faults penetrating through the crust is an important feature of deep-water basin.The study suggests that the broad-deep Baiyun sag provides great accommodation space for the development of massive deltaic-lacustrine deposition system and hydrocarbon source rocks.The differentiated lithospheric thinning also resulted in the different thermal subsidence during post-rifting period,and then controlled the development of continental shelf break and deep-water reservoir sedimentary environment.The high heat flow background caused by the strong thinning of lithosphere and the rise of mantle source resulted in particularities in the reservoir diagenesis,hydrocarbon generation process and accumulation of deep-water area in northern South China Sea.
基金financially supported by the National Natural Science Foundation of China(grants No.41376062,91328205,41206039)Project of the Tectonic Evolution of China Sea and its adjacent areas(grant No.GZH201100205)+1 种基金Public Science and Technology Research Funds Projects of Ocean(grant No.201405032)sponsored by NSFC and Special Fund for strategic pilot technology,CAS
文摘Dongsha waters are poorly studied for gas hydrates. Previous multi-channel seismic reflection and Chirp sub- bottom profiles show that numerous submarine mounds stand up to 100 m high above the seafloor over the continental slope of the SW Dongsha Island in northern margin of the South China Sea (SCS). These mounds are characterized by hardened seabed, seafloor gas venting and folded structures, which implies the existence of active mud volcanoes. This work aims to confirm this speculation by seafloor sample dredging and to explore the potential of gas hydrates.
基金funded by Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(GML2019ZD0201,GML2019ZD0104)Finance Science and Technology Project of Hainan Province(ZDKJ202019).
文摘Great advancement has been made on natural gas hydrates exploration and test production in the northern South China Sea.However,there remains a lot of key questions yet to be resolved,particularly about the mechanisms and the controls of gas hydrates enrichment.Numerical simulaution would play signficant role in addressing these questions.This study focused on the gas hydrate exploration in the Shenhu Area,Northern South China Sea.Based on the newly obtained borehole and multichannel reflection seismic data,the authors conducted an integrated 3D basin modeling study on gas hydrate.The results indicate that the Shenhu Area has favorable conditions for gas hydrate accumulation,such as temperature,pressure,hydrocarbon source,and tectonic setting.Gas hydrates are most concentrated in the Late Miocene strata,particularly in the structual highs between the Baiyun Sag and the Liwan Sag,and area to the south of it.It also proved the existence of overpressure in the main sag of source rocks,which was subject to compaction disequilibrium and hydrocarbon generation.It also shown that the regional fault activity is not conducive to gas hydrate accumulation due to excess gas seepage.The authors conjecture that fault activity may slightly weaken overpressure for the positive effect of hydrocarbon expulsion and areas lacking regional fault activity have better potential.
文摘More than 4 000 km 48-channel seismic reflection data from the central region of the South China Sea have been interpreted. Five seismic interfaces have been distinguished, named T1, T2, T4, T6 and Tg respectively Meanwhile, five seismic sequences numbered I - V have been divided with the ages of Quaternary and Pliocene, Later Mocene, Earlier and Middle Miocene, Oligocene and Pre- Oligocene separately. Sequences I-II overlie all parts of the area. In the continental slope and island slope, Sequences III-V are mainly found in the grabens. Sequence III is found at moot profiles of the deep-sea basin, and Sequnce IV is seen not only at the margins of the east subbasin but also at the margins of the southwest subbasin. Strong reflection from Moho is found at most profiles of the deep-sea basin. The depth of Moho varies between 10 and 12 km, with a thickness of 6- 8 km for the crust. Calculated by age-basement depth correlation formula, the age of basaltic basement in the southwest subbasin is 51-39 Ma. It is indicated that the evolution of the southwest subbasin is simultaneous with or earlier than that of the east subbasin.
基金China National Major Special Project under contract No.2011ZX05025-002
文摘The deepwater of the northwestern South China Sea is located in the central to southern parts of the Qiongdongnan Basin (QDN Basin), which is a key site for hydrocarbon exploration in recent years. In this study, the authors did a comprehensive analysis of gravity-magnetic data, extensive 3D seismic survey, cores and cuttings, paleontology and geochemical indexes, proposed the mechanism of natural gas origin, identified different oil and gas systems, and established the model of hydrocarbon accumulations in the deep-water region. Our basin tectonic simulation indicates that the evolution of QDN Basin was controlled by multiple-phased tectonic movements, such as Indochina-Eurasian Plate collision, Tibetan Uplift, Red River faulting and the expansion of the South China Sea which is characterized by Paleogene rifting, Neogene depression, and Eocene intensive faulting and lacustrine deposits. The drilling results show that this region is dominated by marine- terrestrial transitional and neritic-bathyal facies from the early Oligocene. The Yacheng Formation of the early Oligocene is rich in organic matter and a main gas-source rock. According to the geological-geochemical data from the latest drilling wells, Lingshui, Baodao, Changchang Sags have good hydrocarbon-generating potentials, where two plays from the Paleogene and Neogene reservoirs were developed. Those reservoirs occur in central canyon structural-lithologic trap zone, Changchang marginal trap zone and southern fault terrace of Baodao Sag. Among them, the central canyon trap zone has a great potential for exploration because the various reservoir- forming elements are well developed, i.e., good coal-measure source rocks, sufficient reservoirs from the Neogene turbidity sandstone and submarine fan, faults connecting source rock and reservoirs, effective vertical migration, late stage aggregation and favorable structural-lithological composite trapping. These study results provide an important scientific basis for hydrocarbon exploration in this region, evidenced by the recent discovery of the significant commercial LS-A gas field in the central canyon of the Lingshui Sag.
基金Research in this paper was supported by the National Natural Science Foundation of China (Grant No. 41602251), the Chinese Postdoc Fund, No.58 General Fund, 2015 (No. 2015M582636) and the Research Fund for New Teachers of Xi'an Jiaotong University. We are grateful to CNOOC Research Institute for providing the seismic profiles. We also thank anonymous reviewers for their careful and insightful suggestions on the paper.
文摘The Baiyun Sag, located in the deep-water area of the northern South China Sea, is the largest and deepest subbasin in the Pearl River Mouth Basin and one of the most important hydrocarbon-accumulation depression areas in China. Thermal history is widely thought to be of great importance in oil and gas potential assessment of a basin as it controls the timing of hydrocarbon generation and expulsion from the source rock. In order to unravel the paleo-heat flow of the Baiyun Sag, we first analyzed tectonic subsidence of 55 pseudo-wells constructed based on newly interpreted seismic profiles, along with three drilled wells. We then carried out thermal modeling using the multi-stage finite stretching method and calibrated the results using collected present-day vitrinite reflectance data and temperature data. Results indicate that the first and second heating of the Baiyun Sag after 49 Ma ceased at 33.9 Ma and 23 Ma. Reconstructed average basal paleo- heat flow values at the end of the rifting periods are -57.7- 86.2 mW/m2 and -66.7-97.3 mW/m2, respectively. Following the last heating period at 23 Ma, the study area has undergone a persistent thermal attenuation phase, and basal heat flow has cooled down to ~64.0-79.2 mW/m2 at present.
基金The National Natural Science Foundation of China under contract Nos 41372112 and 91028009the National Key Projects of Oil and Gas under contract No.2011ZX05025-002-02the Open Fund of Key Laboratory of Tectonics and Petroleum Resources(China University of Geosciences),Ministry of Education under contract No.TPR-2012-05
文摘Based on the interpretation of high resolution 2D/3D seismic data, sedimentary filling characteristics and full- filled time of the Central Canyon in different segments in the Qiongdongnan Basin of northwestern South China Sea have been studied. The research results indicate that the initial formation age of the Central Canyon is traced back to 11.6 Ma (T40), at which the canyon began to develop due to the scouring of turbidity currents from west to east. During the period of 11.6-8.2 Ma (T40-T31), strong downcutting by gravity flow occurred, which led to the formation of the canyon. The canyon fillings began to form since 8.2 Ma (T31) and were dominated by turbidite deposits, which constituted of lateral migration and vertical superposition of turbidity channels during the time of 8.2-5.5 Ma. The interbeds of turbidity currents deposits and mass transport deposits (MTDs) were developed in the period of 5.5-3.8 Ma (T30-T28). After then, the canyon fillings were primarily made up of large scale MTDs, interrupted by small scale turbidity channels and thin pelagic mudstones. The Central Canyon can be divided into three types according to the main controlling factors, geomorphology-controlled, fault-controlled and intrusion- modified canyons. Among them, the geomorphology-controlled canyon is developed at the Ledong, Lingshui, Songnan and western Baodao Depressions, situated in a confined basin center between the northern slope and the South Uplift Belt along the Central Depression Belt. The fault-controlled canyon is developed mainly along the deep-seated faults in the Changchang Depression and eastern Baodao Depression. Intrusion-modified canyon is only occurred in the Songnan Low Uplift, which is still mainly controlled by geomorphology, the intrusion just modified seabed morphology. The full-filled time of the Central Canyon differs from west to east, displaying a tendency of being successively late eastward. The geomorphology-controlled canyon was completely filled before 3.8 Ma (T28), but that in intrusion-modified canyon was delayed to 2.4 Ma (T27) because of the uplifted southern canyon wall. To the Changchang Depression, the complete filling time was successively late eastward, and the canyon in eastern Changchang Depression is still not fully filled up to today. Difference in full-filled time in the Central Canyon is mainly governed by multiple sediment supplies and regional tectonic activities. Due to sufficient supply of turbidity currents and MTDs from west and north respectively, western segment of the Central Canyon is entirely filled up earlier. Owing to slower sediment supply rate, together with differential subsidence by deep-seated faults, the full-filled time of the canyon is put off eastwards gradually.
基金This research was jointly supported by the National Key R&D Program of China(2021YFC2800801)the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(GML2019ZD0501)+3 种基金the Guangzhou Basic and Applied Basic Foundation(202102020611)the project of Guangzhou Marine Geological Survey of the China Geology Survey(DD20221700)the Key-Area Research and Development Program of Guangdong Province(2020B1111030003)the High-tech Ship Research Project of the Ministry of Industry and Information Technology(CJ05N20).
文摘Conductor and suction anchor are the key equipment providing bearing capacity in the field of deep-water drilling or offshore engineering,which have the advantages of high operation efficiency and short construction period.In order to drill a horizontal well in the shallow hydrate reservoir in the deep water,the suction anchor wellhead assembly is employed to undertake the main vertical bearing capacity in the second round of hydrate trial production project,so as to reduce the conductor running depth and heighten the kick-off point position.However,the deformation law of the deep-water suction anchor wellhead assembly under the moving load of the riser is not clear,and it is necessary to understand the lateral bearing characteristics to guide the design of its structural scheme.Based on 3D solid finite element method,the solid finite element model of the suction anchor wellhead assembly is established.In the model,the seabed soil is divided into seven layers,the contact between the wellhead assembly and the soil is simulated,and the vertical load and bending moment are applied to the wellhead node to simulate the riser movement when working in the deep water.The lateral bearing stability of conventional wellhead assembly and suction anchor wellhead assembly under the influence of wellhead load is discussed.The analysis results show that the bending moment is the main factor affecting the lateral deformation of the wellhead string;the anti-bending performance from increasing the outer conductor diameter is better than that from increasing the conductor wall thickness;for the subsea wellhead,the suction anchor obviously improves the lateral bearing capacity and reduces the lateral deformation.The conduct of the suction anchor wellhead assembly still needs to be lowered to a certain depth that below the maximum disturbed depth to ensure the lateral bearing stability,Thus,a method for the minimum conductor running depth for the suction anchor wellhead assembly is developed.The field implementations show that compared with the first round of hydrate trial production project,the conductor running depth is increased by 9.42 m,and there is no risk of wellhead overturning during the trial production.The method for determining the minimum conductor running depth in this paper is feasible and will still play an important role in the subsequent hydrate exploration and development.
基金This work was funded by the Key Laboratory of Marine Hydrocarbon Resources and Environmental Geology,Ministry of Land and Resources(MRE201305)the Key Laboratory of Marine Geology and Environment,China Academy of Sciencess(MGE2013KG02).
文摘This study elucidates sedimentary evolution history of the Central Canyon System(CCS),a large axial submarine canyon in the Qiongdongnan Basin(QDNB),northern South China Sea.Thegeomorphological characteristics and infill architectures of the CCS are summarized based on theanalysis of two-and three-dimensional seismic data.Based on a comparative analysis of the CCS indifferent segments and evolutionary stages and in consideration of the tectono-sedimentary conditionsof the QDNB four stages of the sedimentary evolution of the CCS can be divided,i.e.initialdevelopment stage in the Late Miocene(11.6-5.7Ma),erosion-infilling stage in the Early Pliocene(5.7-3.7 Ma),tranquil infilling stage in the Late Pliocene(3.7-1.81 Ma),and rejuvenation stage sincethe Pleistocene(1.81 Ma to present).In the 1ate Middle Miocene(~11.6 Ma),the rudiment of CCswas developed by a regional tectonic transformation in the eastern part of the basin.In the EarlyPliocene,the CCS was further developed from west to east and restrained in the central depressionbelt of the basin due to abundant sediment supplies from the northwestern and northem provenances,the blocking effect of the southern uplift belt,and the restrictive geomorphological features of theeastern part of the basin.In the Late Pliocene,changes in the sedimentary environment resulted in thedevelopment of the CCS in the eastern part of the basin only.Since the Pleistocene,the joint action ofclimatic factors and geomorphological features of the eastern part of the basin led to the rejuvenationof the CCS.
文摘The tectonic cycle of the marginal sea basins in South China Sea(SCS)includes two cycles,i.e.,the formation and contraction of Palaeo-SCS and Neo-SCS.The northern part of SCS is a rift basin on a passive continental margin,while the the Nansha Block is a drifting rift basin.The southern part is a compound compressional basin on an active continental margin;the western part is a shear-extensional basin on a transform continental margin;the eastern part is an accretionary wedge basin on a subduction continental margin.The deep-water basins are mainly distributed on the continental slope and the the Nansha Block.There are three sets of source rocks in the deep-water areas of the northern continental margin in SCS,i.e.,Eocene terrestrial facies,early Oligocene transitional facies and late Oligocene marine facies.A set of Late Cretaceous-Early Oligocene terrestrial marine facies source rocks are developed in the drift-rift basin of SCS.Three sets of Oligocene,early Miocene and Mid-Miocene marine-terrestrial transitional facies source rocks are developed in the deep-water areas of both the southern and western continental margins of SCS.Four sets of reservoirs developed in the northern deep waters of SCS are dominated by deep sea fans.Two sets of reservoirs developed in the the Nansha Block are dominated by delta and biogenic reef.The southern part of SCS is dominated by deep sea fan and biogenic reef.Reservoirs of large channels and other clastic facies were developed in front of the estuaries,while biogenic reef bank was formed in the uplift zone.The hydrocarbon accumulation assemblages are mainly presented as Oligocene-Pliocene in the deep waters on the northern continental margin of SCS,Eocene-Lower Oligocene in the the Nansha Block,Oligocene-Pliocene and Oligocene-Miocene in the deep waters on the southern and western continental margin of SCS,respectively.The major hydrocarbon reservoir types in the deep waters of SCS are related to structural traps,deep water fans and biogenic reefs.The formation of basin,hydrocarbon and reservoir in the deep waters of SCS are controlled by the tectonic cycles of the marginal sea basins,revealing a great potential for hydrocarbon exploration.