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
Based on heavy mineral data in core samples from eleven drillings, supplemented by paleontological, element geochemical and seismic data, the evolution of sediment provenance and environment in the Qiongdongnan Basin ...Based on heavy mineral data in core samples from eleven drillings, supplemented by paleontological, element geochemical and seismic data, the evolution of sediment provenance and environment in the Qiongdongnan Basin （QDNB） was analysed. The results show that the basement in the QDNB was predominantly composed of terrigenous sediments. Since the Oligocene the QDNB has gradually undergone transgressions and evolution processes in sedimentary environment from terrestrial-marine transitional to littoral-neritic, neritic, and bathyal roughly. The water depth showed a gradually increasing trend and was generally greater in the southern region than that in the northern region in the same time. With changes in sedimentary environment, provenances of the strata （from the Yacheng Formation to the Yinggehai Formation） showed principal characteristics of multi-sources, evolving from autochthonous source, short source to distant source step by step. During the Early Oligocene, the sediments were mainly proximal basaltic pyroclastic source and adjacent terrigenous clastic source, afterwards were becoming distant terrigenous clastic sources, including Hainan Island on the north, Yongle Uplift on the south, Shenhu Uplift on the northeast, the Red River System on the northwest and Indochina Peninsula on the southwest, or even a wider region. The Hainan Island provenance began to develop during the Early Oligocene and has become a main provenance in the QDNB since the Middle Miocene. The provenances from Yongle Uplift and Shenhu Uplift most developed from the Late Oligocene to the Early Miocene and gradually subsided during the Middle Miocene. During the Late Miocene, as a main source of sediments filled in the central canyon, the Red River System provenance added to the QDNB massively, whose impact terminated at the end of the Pliocene. The western Yinggehai Basin （YGHB） provenance derived from Indochina Peninsula had developed from the Pliocene on to the Pleistocene. In addition, the material contribution of marine authigenous source to the basin （especially to the southern region） could not be ignored.展开更多
Over the past several years, a number of hydrocarbon reservoirs have been discovered in the deepwater area of Qiongdongnan Basin, northwestern South China Sea. These oil/gas fields demonstrate that the evolution of th...Over the past several years, a number of hydrocarbon reservoirs have been discovered in the deepwater area of Qiongdongnan Basin, northwestern South China Sea. These oil/gas fields demonstrate that the evolution of the deepwater sedimentary environment are controlling the formation and distribution of large-scale clastic reservoirs. Integration between seismic and borehole data were necessary to best clarify the distribution and quality of these deepwater reservoirs. Geochemical and paleobiological evidence from discrete samples was also applied to document specific information regarding the sedimentary environment. Results show that the Qiongdongnan Basin has existed as a thriving marine environment since Oligocene, when several rifting depressions developed throughout the entire Qiongdongnan Basin. Triggered by the faults activities, several distinct provenances supplied the coarse sediments, transporting and depositing them in deep parts of the rifting depressions. A fan delta system then formed nearby the source in the deeper area of these rifting depressions. The sedimentary environment of Qiongdongnan gradiationally became deepwater since early Miocene. Consequently, abundances of sediments were transported from Hainan Island and Southern Uplift, and then sunk into the basin center. The submarine fans revealed by many boreholes in this area verified them as good reservoir. Because the area reached its lowest sea level at late Miocene and the Southern Uplift subsidenced under sea level, not providing any sediment, so that the carbonate mesa and biorhythms characteristic of this area also developed during this period. In the west part of Qiongdongnan Basin, sediments transported from Vietnam increased in response to the Tibetan Uplift. Consequently, a central canyon developed along the center of Qiongdongnan Basin, which has been confirmed by several boreholes as a favorable hydrocarbon reservoir. The clarification of the deepwater sedimentary environment’s evolution is potentially highly beneficial to future hydrocarbon exploration in the deepwater area of Qiongdongnan Basin.展开更多
Using regional geological, newly acquired 2D and 3D seismic, drilling and well log data, especially 2D long cable seismic profiles, the structure and stratigraphy in the deep-water area of Qiongdongnan Basin are inter...Using regional geological, newly acquired 2D and 3D seismic, drilling and well log data, especially 2D long cable seismic profiles, the structure and stratigraphy in the deep-water area of Qiongdongnan Basin are interpreted. The geometry of No.2 fault system is also re-defined, which is an important fault in the central depression belt of the deep-water area in the Qiongdongnan Basin by employing the quantitative analysis techniques of fault activity and backstripping. Furthermore, the dynamical evolution of the No.2 fault sys-tem and its controls on the central depression belt are analyzed. This study indicates that the Qiongdongnan Basin was strongly influenced by the NW-trending tensile stress field during the Late Eocene. At this time, No.2 fault system initiated and was characterized by several discontinuous fault segments, which controlled a series small NE-trending fault basins. During the Oligocene, the regional extensional stress field changed from NW-SE to SN with the oceanic spreading of South China Sea, the early small faults started to grow along their strikes, eventually connected and merged as the listric shape of the No.2 fault system as ob-served today. No.2 fault detaches along the crustal Moho surface in the deep domain of the seismic profiles as a large-scale detachment fault. A large-scale rollover anticline formed in hanging wall of the detachment fault. There are a series of small fault basins in both limbs of the rollover anticline, showing that the early small basins were involved into fold deformation of the rollover anticline. Structurally, from west to east, the central depression belt is characterized by alternatively arranged graben and half-graben. The central depression belt of the Qiongdongnan Basin lies at the extension zone of the tip of the V-shaped northwest-ern ocean sub-basin of the South China Sea, its activity period is the same as the development period of the northwestern ocean sub-basin, furthermore the emplacement and eruption of magma that originated from the mantle below the Moho surface occurred at the region between Songnan-Baodao and Changchang sags, from east to west with the early-stage spreading of the South China Sea. Therefore, this study not only helps in depicting the structural features and evolution of the deep-water basin in the Qiongdongnan Basin, but also provides the geological and structural evidence for establishing a unified model of continental margin extension and oceanic spreading.展开更多
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The National Science and Technology Major Project under contract No.2011ZX05025-002-03
文摘Based on heavy mineral data in core samples from eleven drillings, supplemented by paleontological, element geochemical and seismic data, the evolution of sediment provenance and environment in the Qiongdongnan Basin （QDNB） was analysed. The results show that the basement in the QDNB was predominantly composed of terrigenous sediments. Since the Oligocene the QDNB has gradually undergone transgressions and evolution processes in sedimentary environment from terrestrial-marine transitional to littoral-neritic, neritic, and bathyal roughly. The water depth showed a gradually increasing trend and was generally greater in the southern region than that in the northern region in the same time. With changes in sedimentary environment, provenances of the strata （from the Yacheng Formation to the Yinggehai Formation） showed principal characteristics of multi-sources, evolving from autochthonous source, short source to distant source step by step. During the Early Oligocene, the sediments were mainly proximal basaltic pyroclastic source and adjacent terrigenous clastic source, afterwards were becoming distant terrigenous clastic sources, including Hainan Island on the north, Yongle Uplift on the south, Shenhu Uplift on the northeast, the Red River System on the northwest and Indochina Peninsula on the southwest, or even a wider region. The Hainan Island provenance began to develop during the Early Oligocene and has become a main provenance in the QDNB since the Middle Miocene. The provenances from Yongle Uplift and Shenhu Uplift most developed from the Late Oligocene to the Early Miocene and gradually subsided during the Middle Miocene. During the Late Miocene, as a main source of sediments filled in the central canyon, the Red River System provenance added to the QDNB massively, whose impact terminated at the end of the Pliocene. The western Yinggehai Basin （YGHB） provenance derived from Indochina Peninsula had developed from the Pliocene on to the Pleistocene. In addition, the material contribution of marine authigenous source to the basin （especially to the southern region） could not be ignored.
基金The National Science and Technology Major Project of China under contract No.2011ZX05025-002-02the National Natural Science Foundation of China under contract Nos 41476032 and 41372112
文摘Over the past several years, a number of hydrocarbon reservoirs have been discovered in the deepwater area of Qiongdongnan Basin, northwestern South China Sea. These oil/gas fields demonstrate that the evolution of the deepwater sedimentary environment are controlling the formation and distribution of large-scale clastic reservoirs. Integration between seismic and borehole data were necessary to best clarify the distribution and quality of these deepwater reservoirs. Geochemical and paleobiological evidence from discrete samples was also applied to document specific information regarding the sedimentary environment. Results show that the Qiongdongnan Basin has existed as a thriving marine environment since Oligocene, when several rifting depressions developed throughout the entire Qiongdongnan Basin. Triggered by the faults activities, several distinct provenances supplied the coarse sediments, transporting and depositing them in deep parts of the rifting depressions. A fan delta system then formed nearby the source in the deeper area of these rifting depressions. The sedimentary environment of Qiongdongnan gradiationally became deepwater since early Miocene. Consequently, abundances of sediments were transported from Hainan Island and Southern Uplift, and then sunk into the basin center. The submarine fans revealed by many boreholes in this area verified them as good reservoir. Because the area reached its lowest sea level at late Miocene and the Southern Uplift subsidenced under sea level, not providing any sediment, so that the carbonate mesa and biorhythms characteristic of this area also developed during this period. In the west part of Qiongdongnan Basin, sediments transported from Vietnam increased in response to the Tibetan Uplift. Consequently, a central canyon developed along the center of Qiongdongnan Basin, which has been confirmed by several boreholes as a favorable hydrocarbon reservoir. The clarification of the deepwater sedimentary environment’s evolution is potentially highly beneficial to future hydrocarbon exploration in the deepwater area of Qiongdongnan Basin.
基金The National Science and Technology Major Project of China under contract No.2011ZX05025-002-02the National Natural Sci-ence Foundation of China under contract Nos 41272121,91028009 and 41102071
文摘Using regional geological, newly acquired 2D and 3D seismic, drilling and well log data, especially 2D long cable seismic profiles, the structure and stratigraphy in the deep-water area of Qiongdongnan Basin are interpreted. The geometry of No.2 fault system is also re-defined, which is an important fault in the central depression belt of the deep-water area in the Qiongdongnan Basin by employing the quantitative analysis techniques of fault activity and backstripping. Furthermore, the dynamical evolution of the No.2 fault sys-tem and its controls on the central depression belt are analyzed. This study indicates that the Qiongdongnan Basin was strongly influenced by the NW-trending tensile stress field during the Late Eocene. At this time, No.2 fault system initiated and was characterized by several discontinuous fault segments, which controlled a series small NE-trending fault basins. During the Oligocene, the regional extensional stress field changed from NW-SE to SN with the oceanic spreading of South China Sea, the early small faults started to grow along their strikes, eventually connected and merged as the listric shape of the No.2 fault system as ob-served today. No.2 fault detaches along the crustal Moho surface in the deep domain of the seismic profiles as a large-scale detachment fault. A large-scale rollover anticline formed in hanging wall of the detachment fault. There are a series of small fault basins in both limbs of the rollover anticline, showing that the early small basins were involved into fold deformation of the rollover anticline. Structurally, from west to east, the central depression belt is characterized by alternatively arranged graben and half-graben. The central depression belt of the Qiongdongnan Basin lies at the extension zone of the tip of the V-shaped northwest-ern ocean sub-basin of the South China Sea, its activity period is the same as the development period of the northwestern ocean sub-basin, furthermore the emplacement and eruption of magma that originated from the mantle below the Moho surface occurred at the region between Songnan-Baodao and Changchang sags, from east to west with the early-stage spreading of the South China Sea. Therefore, this study not only helps in depicting the structural features and evolution of the deep-water basin in the Qiongdongnan Basin, but also provides the geological and structural evidence for establishing a unified model of continental margin extension and oceanic spreading.
