Since 2017, a plenty of gas hydrates have been drilled in a new area of Shenhu, and good heterogeneity has been found throughout the spatial distribution of the reservoir. After distinguishing different sedimentary se...Since 2017, a plenty of gas hydrates have been drilled in a new area of Shenhu, and good heterogeneity has been found throughout the spatial distribution of the reservoir. After distinguishing different sedimentary sequence types and matching their formation with slope deposition settings, this study proposes three mass transport deposit(MTD) patterns related to canyon activity that occurred contemporaneously or epigenetically with it: well preserved MTDs, MTDs eroded by canyon migration, and MTDs dislocated by contemporaneous faults. Based on seismic reflection characteristics, this study proposed methods of quantitatively analyzing sedimentary factors,such as measuring the turbidities flow rate in the canyon, and results are interpreted with respect to canyon activity. Combining the above parameters and their relationship with gas hydrate accumulation, fine-grained seals overlapping coarse MTDs reservoirs are found to be indispensable to gas hydrate accumulation, as they prevent the release of free gas. Based on grain size data of hydrate samples from drilling wells, multi-layered gas hydrate reservoirs capped by fine-grained sediments and overlapping mud show favorable hydrate-bearing prospects. The release of gas hydrates, however, is mostly caused by the lack of mud sealing in relation to canyon activity, such as turbidities flow erosion and contemporaneous fault breaking. Canyon migration with respect to MTDs may be the actual cause of erosion of overlapping syn-sedimentary layers, and high bottom flows may contribute to an increase in the release of free gas. It is believed that contemporaneous faults caused by unstable canyon walls may break the muddy over layers and decrease the accumulation pressure of gas hydrate bearing.Thus, according to the sedimentary characteristics of MTDs and the hydrate accumulation process, three responding accumulation or releasing patterns are proposed, which respond to the different types of MTDs distinguished above: a well-preserved MTD accumulation pattern; a canyon migration eroded MTD release pattern; and a micro-contemporaneous fault dislocated MTD release pattern.展开更多
Natural gas hydrate(NGH) is one of the important clean energy at present and even in the future. The study of its sedimentary environment and minerogenetic condition has long been a hot issue that has received much co...Natural gas hydrate(NGH) is one of the important clean energy at present and even in the future. The study of its sedimentary environment and minerogenetic condition has long been a hot issue that has received much concern from geologists all over the world. China has successfully obtained the samples of NGH in Shenhu and Dongsha sea areas in 2007, 2013 and 2015, respectively. From this, the continental slope north of the South China Sea becomes an important test site for the study of NGH sedimentary genesis and minerogenetic condition. NGH has been found in Shenhu, Dongsha and Qiongdongnan areas within the continental slope north of South China Sea,at different depths of water, with different sedimentary characteristics, gas genesis, and minerogenetic conditions.Using a seismic sedimentology theory, combining seismic facies results of each facies, sedimentary facies and evolution of each area are documented in turn establishing a sedimentary model by considering palaeogeomorphology, sea level change and tectonic movement. The channel system and MTD(Mass Transport Deposition) system among these three areas were compared focusing on the developing position, appearance and controlling factors. Relative location among three areas is firstly defined that Dongsha area in a nearprovenance steep upper slope, Shenhu area in a normal gentle slope and Qiongdongnan area in an awayprovenance flat plain. Besides, their channel systems are classified into erosional, erosional-aggradational and aggradational channel, and MTD systems into headwall domain, translational domain and toe domain.展开更多
While deltas fed by seasonal rivers are common in modem sedimentary environments,their characteristics remain unclear as compared to those fed by perennial rivers.This study identifies a small delta discharged by a se...While deltas fed by seasonal rivers are common in modem sedimentary environments,their characteristics remain unclear as compared to those fed by perennial rivers.This study identifies a small delta discharged by a seasonal stream flowing into Daihai Lake,in northern China,which is driven by ephemeral and high-energy flood events.Detailed 3D facies architecture was analyzed using ground-penetrating radar (GPR) and sedimentary logs from outcrop and trenches.Four types of radar surfaces,including truncations of underlying inclined strata,weak reflections,and depositional surface of downlap and onlap,were identified.Six radar facies (highangle obliquetangential,low-angle subparallel,gently plane parallel,plane-parallel,chaotic,and continuous strong reflection) were identified based on distinctive reflections,including amplitude,continuity,dip,and termination patterns.Five depositional units (Unit A to E) were documented from proximal to distal delta.Seasonal discharge signatures include significant grain-size decrease over short distance,abundant Froude supercritical flow sedimentary structures,poorly developed barforms,and small-scale scour and fill structures.Records of lake-level and sediment budget were evaluated over the past 60 years.In highstand stage (1960- 1980),amalgamated channel (Units A and B),and delta front (Unit C) were deposited.In slope stage (1980-1996),the lower deposits (Units A,B,C) were eroded by Unit D with a distinct truncation surface.In lowstand stage,most eroded sediments bypassed the incised channel and accumulated in the distal part,in which a new depositional unit was formed (Unit E).The model demonstrates that deltas fed by seasonal rivers tend to accumulate large amounts of sediments carried by high magnitude floods within short periods.展开更多
The Mesozoic fan deltas in the north-west margin of the Junggar Basin,as important petroleum reservoirs,exhibited complex facies change and internal structures with strong heterogeneity which were controlled by the tr...The Mesozoic fan deltas in the north-west margin of the Junggar Basin,as important petroleum reservoirs,exhibited complex facies change and internal structures with strong heterogeneity which were controlled by the transformation of slope-patterns,bringing great challenges to the study of sedimentary characteristics.The Upper Karamay Formation at north-west margin of the Junggar Basin was the objective in this paper which attempts to clarify the mechanism of sedimentary response and sand-body distribution of fan delta systems under the control of slope-pattern change.Based on a data set of cores,well logs and seismic,two types of slope-pattern were identified in the study area,which include steep-to-gentle in the south and gentle-to-steep in the north.The control of difference slope-patterns on the sand-body distribution was clarified based on the analysis of the sedimentary dynamics,facies characteristics,and depositional evolution of the fan deltas.The study shows that the transport mechanism of sediments on the steep-slope was dominated by debris flows,developing coarse-grained,thick-bedded lobes with poor structural maturity of clasts.On the gentle-slope,the deposition was dominated by hyperconcentrated-traction currents,forming relatively fine-grained,thin-bedded lobes with increased sandy matrix.The sand-bodies show frequent bar-channel transformation and channel down-cutting under the steep slope setting,which exhibit migration of isolated river channels on the gentle slopes.Under the steep-to-gentle pattern,the coase-grained sediments were mainly accumulated at slope toe,generally developed equiaxial lobes.However,the coarse-grained clasts were preserved both at proximal and distal lobes on the gentle-to-steep slopes,showing obvious lateral extension of the fan delta.The slope patterns controlled sedimentary respond rates of the fan deltas during lake level change.By comparing the modern cases of fan systems worldwide,the control of slope patterns on deposition of coarse-grained fans was clarified,providing insight into hydrocarbon exploration on basin margins.展开更多
The work presents the sedimentology and depositional results of the turbidity flow from Miocene to Pliocene along the North Slope of South China Sea(SCS).The integration of the core-log-seismic data has enabled us to ...The work presents the sedimentology and depositional results of the turbidity flow from Miocene to Pliocene along the North Slope of South China Sea(SCS).The integration of the core-log-seismic data has enabled us to clarify turbidity flow with different density and characterize their corresponding seismic geomorphic sedimentation.Based on the differences between the initial density and the later,we classified the turbidity flow into two types,namely:low-and high-density flow with coarse grain injection.According to the hydrodynamic numerical simulation results,we constructed different subcritical turbidity flow models with various density and rebuilt the depositional pattern along the slope.As to the numerical simulation model,we introduced the erosion rate into the classical full Reynolds-averaged N-S(RANS)equation,which is suitable to the deep-sea slope area.Through comparison of the above simulation models,the results show that the high-density turbidites with coarse-grained injection are mostly developed with lower vertical erosion rates and higher lateral abrasion rates.They are characterized with multi-branched and lobe-shaped sedimentary volumes,while low-density turbidites with coarse-grained injection are characterized with higher vertical erosion rates and lower lateral abrasion rates.And this kind of turbidites can generate single-branched and banding deposits.In addition,the fluctuating sea levels and the varying topographies are important to influence the subcritical turbidity flow models in the deep-water slope.展开更多
Gas hydrate samples were first obtained in the Dongsha area,South China Sea(GMGS2)in 2013.High-resolution 3D seismic data in the area show various small 1andslide bodies developedas huge mass transport deposits.These ...Gas hydrate samples were first obtained in the Dongsha area,South China Sea(GMGS2)in 2013.High-resolution 3D seismic data in the area show various small 1andslide bodies developedas huge mass transport deposits.These bodies are divided into seven types on the basis of theirshapes,intermal structures and geneses(slide,collapse and deformation above BSRs,as well asthe slump wedge,lens,block and sheet below BSRs).Based on this classification,detailed studieswere conducted,including measurements of the slump body sizes and slope gradients of landslides,depiction of their three-dimensional characteristics,and research on the landslide distribution.Todetermine the genetic differences of these seven types,this study analyses the possibility of verticalflow-pattern-transformation and mechanisms of submarine landsltide formation.Results show that thedominant factor influencing the submarine landslides in the Dongsha area is the free gas emitted fromgas hydrate decomposition,with possible fransformation between flow patterns.Finally,there are twokinds of relationships between submarine landslides and BSRs since the free gas either influences thesubmarine landslide bodies below or above BSRs,resulting in two types of submarine landslide bodyassociations:Type A is characterized by submarine slide above BSRs and slump lens below BSRs,whereas Type B shows deformation above BSRs and slump blocks below BSRs.Type Ais favourablefor gas exploration because it indicates less decomposition and better sealing of gas hydrate layers.展开更多
The drilling areas in Shenhu and Dongsha,South China Sea,studied from 2007 to 2015,reveal great heterogeneity in the spatial distribution of the gas hydrate reservoir.Various types of mass-transport complexes(MTCs)wer...The drilling areas in Shenhu and Dongsha,South China Sea,studied from 2007 to 2015,reveal great heterogeneity in the spatial distribution of the gas hydrate reservoir.Various types of mass-transport complexes(MTCs)were developed in the study areas,which served as ideal reservoirs.To conduct exploration in these areas,it is necessary to study the different types of MTCs and the corresponding gashydrate accumulations.By integrating seismic reflection and log coring data,we classified three types of MTCs according to their stress distribution:the tension,extrusion,and shear types,and their corresponding gashydrate accumulation patterns.The results show that the accumulation of the gas-hydrate varies with the type of MTC and stress distribution depending on the MTC’s position(e.g.,in the headwall,translational,or toe areas).Owing to this variance of the MTC’s position,the corresponding kinemics situation in the MTCs also varies.Accordingly,we determined the corresponding location in which the gashydrate develops for various types of MTCs.Based on the bottom simulating reflectors(BSRs)and the hydrate core and image logging data,the gashydrate reservoir shows an obvious heterogeneity in various types of MTCs.The gashydrate in the tension-type MTCs are mostly borne in the toe and the headwall parts.In extrusion-type MTCs,the translational and toe parts constitute an ideal hydrate reservoir.In shear-type MTCs,the headwall and toe parts’coarse-grained sediments show an obviously hydrate response.After comparing the gashydrate saturation and MTCs morphology statics data,we were able to quantitatively prove that the main factors determining gashydrate accumulation in the different types of MTCs are the fault displacement,sedimentary rate,and flow erosion rate.展开更多
Determining the origin of beach ridges in lacustrine basins can often be problematic. The sedimen- tary processes responsible for formation of beach ridges on the north shore of Huangqihai Lake were investigated by us...Determining the origin of beach ridges in lacustrine basins can often be problematic. The sedimen- tary processes responsible for formation of beach ridges on the north shore of Huangqihai Lake were investigated by using ground penetrating radar （GPR）. A 400 MHz GPR antenna was used to achieve a high vertical resolution of 0.044）.08 m. The radar stratigraphy was then determined using principles of seismic stratigraphy. The radar facies （RF） were determined by analyzing internal configuration and continuity of reflections, as well as reflection termination patterns. The identified RF fall into three groups （inclined, horizontal and irregular）. The inclined group consists of RF that display inclined reflections. The horizontal group consists of RF that exhibit predominantly horizontal reflections. In the irregular group, the reflections are typically weak. RF with reflections with gently landward dips in the shore-normal profile are interpreted as washover sheet deposits. RF with steeply landward-dipping and imbricated reflections are interpreted as washover lobes. Washover sheets develop when overwash fails to enter a significant body of water and sedimentation takes place entirely on the relatively flattened topography. Washover lobe development occurs when overwash enters a region in which topography dips steeply landward, and sedimentation takes place on the surface of washover sheets or previous washover lobes. The beach-ridge deposits are interpreted as being formed entirely from vertically and laterally stacked washover sheets and washover lobes. They were formed by wave-dominated processes and secondary overwash processes supplemented by longshore currents.展开更多
Deltaic sedimentary systems form the most favorable hydrocarbon reservoirs in continental faulted lacustrine basins,and their types and controlling factors directly affect the distribution of hydrocarbons.The systemat...Deltaic sedimentary systems form the most favorable hydrocarbon reservoirs in continental faulted lacustrine basins,and their types and controlling factors directly affect the distribution of hydrocarbons.The systematic study of typical modern delta deposition provides significant guidance regarding the distribution of oil and gas reservoirs in the subsurface.For this reason,the Heima River delta in Qinghai Lake,which features multiple sediment sources and clear sedimentary evolution stages,was selected for this research.A detailed study of the sedimentology and architectural characteristics of the Heimahe delta in Qinghai Lake was conducted.A total of 4 types of gravel facies,4 types of sand facies,and 2 types of mud facies were identified.This study also focuses on recognizing the architectural elements within channels and bars.The delta plain features debris-flow,switched,and migrated channels and vertical and bilateral aggradation bars.The delta front features migrated and filled channels and bilateral and lateral aggradation bars.Twenty-two representative outcrop sections were selected.Detailed observation and analysis of these sections revealed three stages:the progradation to aggradation(PA)stage,in which the deposits show evidence of sigmoid-type and coarse-grained sedimentation;the retrogradation(R)stage,which is characterized by imbricated regression;and the aggradation to progradation and degradation(APD)stage,which is characterized by a terraced-stepping,progression stacking pattern.Based on the integrated analysis of the sedimentary environment,outcrop lithofacies associations,architecture stacking patterns,fossils and bioclasts,we identified diverse depositional associations and constructed a sedimentary evolution model of the depositional system in this area.We suggest that the depositional system transitioned from an early single-provenance gravel-rich fan delta to a multi-provenance mud-rich delta and that two factors mainly controlled the transition:the southern boundary fault activity and lake level variations.The contemporaneous activity of the fault increased the accommodation in the low-stand systems tract,which resulted in continuous coarse-sediment deposition.展开更多
文摘Since 2017, a plenty of gas hydrates have been drilled in a new area of Shenhu, and good heterogeneity has been found throughout the spatial distribution of the reservoir. After distinguishing different sedimentary sequence types and matching their formation with slope deposition settings, this study proposes three mass transport deposit(MTD) patterns related to canyon activity that occurred contemporaneously or epigenetically with it: well preserved MTDs, MTDs eroded by canyon migration, and MTDs dislocated by contemporaneous faults. Based on seismic reflection characteristics, this study proposed methods of quantitatively analyzing sedimentary factors,such as measuring the turbidities flow rate in the canyon, and results are interpreted with respect to canyon activity. Combining the above parameters and their relationship with gas hydrate accumulation, fine-grained seals overlapping coarse MTDs reservoirs are found to be indispensable to gas hydrate accumulation, as they prevent the release of free gas. Based on grain size data of hydrate samples from drilling wells, multi-layered gas hydrate reservoirs capped by fine-grained sediments and overlapping mud show favorable hydrate-bearing prospects. The release of gas hydrates, however, is mostly caused by the lack of mud sealing in relation to canyon activity, such as turbidities flow erosion and contemporaneous fault breaking. Canyon migration with respect to MTDs may be the actual cause of erosion of overlapping syn-sedimentary layers, and high bottom flows may contribute to an increase in the release of free gas. It is believed that contemporaneous faults caused by unstable canyon walls may break the muddy over layers and decrease the accumulation pressure of gas hydrate bearing.Thus, according to the sedimentary characteristics of MTDs and the hydrate accumulation process, three responding accumulation or releasing patterns are proposed, which respond to the different types of MTDs distinguished above: a well-preserved MTD accumulation pattern; a canyon migration eroded MTD release pattern; and a micro-contemporaneous fault dislocated MTD release pattern.
文摘Natural gas hydrate(NGH) is one of the important clean energy at present and even in the future. The study of its sedimentary environment and minerogenetic condition has long been a hot issue that has received much concern from geologists all over the world. China has successfully obtained the samples of NGH in Shenhu and Dongsha sea areas in 2007, 2013 and 2015, respectively. From this, the continental slope north of the South China Sea becomes an important test site for the study of NGH sedimentary genesis and minerogenetic condition. NGH has been found in Shenhu, Dongsha and Qiongdongnan areas within the continental slope north of South China Sea,at different depths of water, with different sedimentary characteristics, gas genesis, and minerogenetic conditions.Using a seismic sedimentology theory, combining seismic facies results of each facies, sedimentary facies and evolution of each area are documented in turn establishing a sedimentary model by considering palaeogeomorphology, sea level change and tectonic movement. The channel system and MTD(Mass Transport Deposition) system among these three areas were compared focusing on the developing position, appearance and controlling factors. Relative location among three areas is firstly defined that Dongsha area in a nearprovenance steep upper slope, Shenhu area in a normal gentle slope and Qiongdongnan area in an awayprovenance flat plain. Besides, their channel systems are classified into erosional, erosional-aggradational and aggradational channel, and MTD systems into headwall domain, translational domain and toe domain.
基金the National Natural Science Foundation of China (Grant No.41602117)the opening foundation of the Key Laboratory of Marine Sedimentology & Environmental Geology,SOA (No.MASEG201706).
文摘While deltas fed by seasonal rivers are common in modem sedimentary environments,their characteristics remain unclear as compared to those fed by perennial rivers.This study identifies a small delta discharged by a seasonal stream flowing into Daihai Lake,in northern China,which is driven by ephemeral and high-energy flood events.Detailed 3D facies architecture was analyzed using ground-penetrating radar (GPR) and sedimentary logs from outcrop and trenches.Four types of radar surfaces,including truncations of underlying inclined strata,weak reflections,and depositional surface of downlap and onlap,were identified.Six radar facies (highangle obliquetangential,low-angle subparallel,gently plane parallel,plane-parallel,chaotic,and continuous strong reflection) were identified based on distinctive reflections,including amplitude,continuity,dip,and termination patterns.Five depositional units (Unit A to E) were documented from proximal to distal delta.Seasonal discharge signatures include significant grain-size decrease over short distance,abundant Froude supercritical flow sedimentary structures,poorly developed barforms,and small-scale scour and fill structures.Records of lake-level and sediment budget were evaluated over the past 60 years.In highstand stage (1960- 1980),amalgamated channel (Units A and B),and delta front (Unit C) were deposited.In slope stage (1980-1996),the lower deposits (Units A,B,C) were eroded by Unit D with a distinct truncation surface.In lowstand stage,most eroded sediments bypassed the incised channel and accumulated in the distal part,in which a new depositional unit was formed (Unit E).The model demonstrates that deltas fed by seasonal rivers tend to accumulate large amounts of sediments carried by high magnitude floods within short periods.
基金supported by the National Natural Science Foundation of China(Grant No.42272124)the Fundamental Research Funds for the Central Universities(No.2-9-2019-100)+1 种基金the National Major Research Program Science and Technology of China(No.2017ZX05001-002)the Key laboratory of marine reservoir evolution and hydrocarbon enrichment mechanism,Ministry of Education.
文摘The Mesozoic fan deltas in the north-west margin of the Junggar Basin,as important petroleum reservoirs,exhibited complex facies change and internal structures with strong heterogeneity which were controlled by the transformation of slope-patterns,bringing great challenges to the study of sedimentary characteristics.The Upper Karamay Formation at north-west margin of the Junggar Basin was the objective in this paper which attempts to clarify the mechanism of sedimentary response and sand-body distribution of fan delta systems under the control of slope-pattern change.Based on a data set of cores,well logs and seismic,two types of slope-pattern were identified in the study area,which include steep-to-gentle in the south and gentle-to-steep in the north.The control of difference slope-patterns on the sand-body distribution was clarified based on the analysis of the sedimentary dynamics,facies characteristics,and depositional evolution of the fan deltas.The study shows that the transport mechanism of sediments on the steep-slope was dominated by debris flows,developing coarse-grained,thick-bedded lobes with poor structural maturity of clasts.On the gentle-slope,the deposition was dominated by hyperconcentrated-traction currents,forming relatively fine-grained,thin-bedded lobes with increased sandy matrix.The sand-bodies show frequent bar-channel transformation and channel down-cutting under the steep slope setting,which exhibit migration of isolated river channels on the gentle slopes.Under the steep-to-gentle pattern,the coase-grained sediments were mainly accumulated at slope toe,generally developed equiaxial lobes.However,the coarse-grained clasts were preserved both at proximal and distal lobes on the gentle-to-steep slopes,showing obvious lateral extension of the fan delta.The slope patterns controlled sedimentary respond rates of the fan deltas during lake level change.By comparing the modern cases of fan systems worldwide,the control of slope patterns on deposition of coarse-grained fans was clarified,providing insight into hydrocarbon exploration on basin margins.
基金This research was sponsored by the National 127 Project(No.G72011003-05-02-02)National Natural Science Foundation of China(No.41572080)the Major State Science and Technology Research Program(No.2016ZX05024002-002).
文摘The work presents the sedimentology and depositional results of the turbidity flow from Miocene to Pliocene along the North Slope of South China Sea(SCS).The integration of the core-log-seismic data has enabled us to clarify turbidity flow with different density and characterize their corresponding seismic geomorphic sedimentation.Based on the differences between the initial density and the later,we classified the turbidity flow into two types,namely:low-and high-density flow with coarse grain injection.According to the hydrodynamic numerical simulation results,we constructed different subcritical turbidity flow models with various density and rebuilt the depositional pattern along the slope.As to the numerical simulation model,we introduced the erosion rate into the classical full Reynolds-averaged N-S(RANS)equation,which is suitable to the deep-sea slope area.Through comparison of the above simulation models,the results show that the high-density turbidites with coarse-grained injection are mostly developed with lower vertical erosion rates and higher lateral abrasion rates.They are characterized with multi-branched and lobe-shaped sedimentary volumes,while low-density turbidites with coarse-grained injection are characterized with higher vertical erosion rates and lower lateral abrasion rates.And this kind of turbidites can generate single-branched and banding deposits.In addition,the fluctuating sea levels and the varying topographies are important to influence the subcritical turbidity flow models in the deep-water slope.
文摘Gas hydrate samples were first obtained in the Dongsha area,South China Sea(GMGS2)in 2013.High-resolution 3D seismic data in the area show various small 1andslide bodies developedas huge mass transport deposits.These bodies are divided into seven types on the basis of theirshapes,intermal structures and geneses(slide,collapse and deformation above BSRs,as well asthe slump wedge,lens,block and sheet below BSRs).Based on this classification,detailed studieswere conducted,including measurements of the slump body sizes and slope gradients of landslides,depiction of their three-dimensional characteristics,and research on the landslide distribution.Todetermine the genetic differences of these seven types,this study analyses the possibility of verticalflow-pattern-transformation and mechanisms of submarine landsltide formation.Results show that thedominant factor influencing the submarine landslides in the Dongsha area is the free gas emitted fromgas hydrate decomposition,with possible fransformation between flow patterns.Finally,there are twokinds of relationships between submarine landslides and BSRs since the free gas either influences thesubmarine landslide bodies below or above BSRs,resulting in two types of submarine landslide bodyassociations:Type A is characterized by submarine slide above BSRs and slump lens below BSRs,whereas Type B shows deformation above BSRs and slump blocks below BSRs.Type Ais favourablefor gas exploration because it indicates less decomposition and better sealing of gas hydrate layers.
基金This research was sponsored by the National 127 Project(No.GZ2011003-05-02-02)National Natural Science Foundation of China(No.41572080),as well as the Major State Science and Technology Research Program(No.2016ZX05024002-002).The authors would like to thank the Guangzhou Marine Geological Survey for providing the geological and seismic data used in this work.We would also like to acknowledge the gas hydrate science team of China University of Geoscience(Beijing).
文摘The drilling areas in Shenhu and Dongsha,South China Sea,studied from 2007 to 2015,reveal great heterogeneity in the spatial distribution of the gas hydrate reservoir.Various types of mass-transport complexes(MTCs)were developed in the study areas,which served as ideal reservoirs.To conduct exploration in these areas,it is necessary to study the different types of MTCs and the corresponding gashydrate accumulations.By integrating seismic reflection and log coring data,we classified three types of MTCs according to their stress distribution:the tension,extrusion,and shear types,and their corresponding gashydrate accumulation patterns.The results show that the accumulation of the gas-hydrate varies with the type of MTC and stress distribution depending on the MTC’s position(e.g.,in the headwall,translational,or toe areas).Owing to this variance of the MTC’s position,the corresponding kinemics situation in the MTCs also varies.Accordingly,we determined the corresponding location in which the gashydrate develops for various types of MTCs.Based on the bottom simulating reflectors(BSRs)and the hydrate core and image logging data,the gashydrate reservoir shows an obvious heterogeneity in various types of MTCs.The gashydrate in the tension-type MTCs are mostly borne in the toe and the headwall parts.In extrusion-type MTCs,the translational and toe parts constitute an ideal hydrate reservoir.In shear-type MTCs,the headwall and toe parts’coarse-grained sediments show an obviously hydrate response.After comparing the gashydrate saturation and MTCs morphology statics data,we were able to quantitatively prove that the main factors determining gashydrate accumulation in the different types of MTCs are the fault displacement,sedimentary rate,and flow erosion rate.
基金This paper was supported by the State Scholarship Fund （Grant No. 201406400030）, the National Natural Science Foundation of China （Grant No. 41072084） and Research Fund for the Doctoral Program of Higher Education （Grant No. 20120022130002）. The authors sincerely thank Professor Lars B. Clemmensen of University of Copenhagen for his constructive idea. The authors also thank Beibei Liu, Yonghui Du, Zhaopu Gao and Yanan Miao for their assistance in the field and laboratory. Cliff thanks the Charles T. McCord Chair in Petroleum Geology for support. The authors also thank two anonymous reviewers.
文摘Determining the origin of beach ridges in lacustrine basins can often be problematic. The sedimen- tary processes responsible for formation of beach ridges on the north shore of Huangqihai Lake were investigated by using ground penetrating radar （GPR）. A 400 MHz GPR antenna was used to achieve a high vertical resolution of 0.044）.08 m. The radar stratigraphy was then determined using principles of seismic stratigraphy. The radar facies （RF） were determined by analyzing internal configuration and continuity of reflections, as well as reflection termination patterns. The identified RF fall into three groups （inclined, horizontal and irregular）. The inclined group consists of RF that display inclined reflections. The horizontal group consists of RF that exhibit predominantly horizontal reflections. In the irregular group, the reflections are typically weak. RF with reflections with gently landward dips in the shore-normal profile are interpreted as washover sheet deposits. RF with steeply landward-dipping and imbricated reflections are interpreted as washover lobes. Washover sheets develop when overwash fails to enter a significant body of water and sedimentation takes place entirely on the relatively flattened topography. Washover lobe development occurs when overwash enters a region in which topography dips steeply landward, and sedimentation takes place on the surface of washover sheets or previous washover lobes. The beach-ridge deposits are interpreted as being formed entirely from vertically and laterally stacked washover sheets and washover lobes. They were formed by wave-dominated processes and secondary overwash processes supplemented by longshore currents.
基金co-funded by the Natural Science Foundation of China(Grant Nos.42172112 and 42272124)Fundamental Research Funds for the Central Universities(No.2-9-2019-100)Major State Science and Technology Research Program(Nos.2016ZX05024-002 and 2017ZX05001-002).
文摘Deltaic sedimentary systems form the most favorable hydrocarbon reservoirs in continental faulted lacustrine basins,and their types and controlling factors directly affect the distribution of hydrocarbons.The systematic study of typical modern delta deposition provides significant guidance regarding the distribution of oil and gas reservoirs in the subsurface.For this reason,the Heima River delta in Qinghai Lake,which features multiple sediment sources and clear sedimentary evolution stages,was selected for this research.A detailed study of the sedimentology and architectural characteristics of the Heimahe delta in Qinghai Lake was conducted.A total of 4 types of gravel facies,4 types of sand facies,and 2 types of mud facies were identified.This study also focuses on recognizing the architectural elements within channels and bars.The delta plain features debris-flow,switched,and migrated channels and vertical and bilateral aggradation bars.The delta front features migrated and filled channels and bilateral and lateral aggradation bars.Twenty-two representative outcrop sections were selected.Detailed observation and analysis of these sections revealed three stages:the progradation to aggradation(PA)stage,in which the deposits show evidence of sigmoid-type and coarse-grained sedimentation;the retrogradation(R)stage,which is characterized by imbricated regression;and the aggradation to progradation and degradation(APD)stage,which is characterized by a terraced-stepping,progression stacking pattern.Based on the integrated analysis of the sedimentary environment,outcrop lithofacies associations,architecture stacking patterns,fossils and bioclasts,we identified diverse depositional associations and constructed a sedimentary evolution model of the depositional system in this area.We suggest that the depositional system transitioned from an early single-provenance gravel-rich fan delta to a multi-provenance mud-rich delta and that two factors mainly controlled the transition:the southern boundary fault activity and lake level variations.The contemporaneous activity of the fault increased the accommodation in the low-stand systems tract,which resulted in continuous coarse-sediment deposition.
