Lacustrine gravity-flow deposits have enormous hydrocarbon potential.However,their depositional architecture has long been considered very complicated and is controlled by various factors,making petroleum exploration ...Lacustrine gravity-flow deposits have enormous hydrocarbon potential.However,their depositional architecture has long been considered very complicated and is controlled by various factors,making petroleum exploration and development highly challenging.The influence of palaeogeomorphology on the extent and formation mechanisms of lacustrine gravity-flow deposits remains poorly understood.This study uses 3D seismic data,well-log data,and core data to characterize the palaeogeomorphology and depositional architecture of the lacustrine gravity-flow deposit of the Yanchang Formation in the Ordos Basin,while analyzing the influence of palaeogeomorphology on the architecture,distribution,and evolution of lacustrine gravity-flow deposit systems.The results showed that three palaeogeomorphologic units—shelf,slope,and basin floor—developed in the basin.Gravity-flow deposits can be further divided into channel and lobe systems.Gravity-flow channel systems have developed in the upper slope area,which include three types of architectural elements:confined channels,unconfined channels,and levee-overbank.As the transport distance of gravity flow increases,the erosion ability of gravity flow weakens,resulting in the terrain formed by gravity flow erosion gradually weakening the constraint on sediment transport.Consequently,gravity-driven flow pathways shift from linear,confined channels to curved,unconfined channels,finally leading to the development of numerous distributary channels.In the lower slope area,gravity flow sediments distribute rapidly and accumulate to form lobes after encountering slope breaks,due to the decrease of dynamics,including three types of architectural elements:distributary channels,lobe axis and lobe fringe.These lobes are tongue-shaped and fan-shaped on the plane.A series of lobes are superimposed and form a lobe complex set.These lobe complex sets are distributed in a branch-like manner.There are many branch-shaped low-bend amplitude channels inside the lobe complex set.Palaeogeomorphology plays an important role in controlling the spatial distribution of depositional architecture.As the slope gradient increases,the influence of slope break on sediment gravity flow weakens,leading to a delay of the sediment gravity flow slumping to the basin bottom.Additionally,the extension length of the channel system on the slope increases.Furthermore,the extension length of the lobes toward the center of the basin also increases.This work improves the fundamental understanding of the depositional architecture of lacustrine gravity-flow deposits and may help enhance sand prediction for the same type deposit reservoirs.展开更多
Fine-grained sediments are widely distributed and constitute the most abundant component in sedi-mentary systems,thus the research on their genesis and distribution is of great significance.In recent years,fine-graine...Fine-grained sediments are widely distributed and constitute the most abundant component in sedi-mentary systems,thus the research on their genesis and distribution is of great significance.In recent years,fine-grained sediment gravity-flows(FGSGF)have been recognized as an important transportation and depositional mechanism for accumulating thick successions of fine-grained sediments.Through a comprehensive review and synthesis of global research on FGSGF deposition,the characteristics,depositional mechanisms,and distribution patterns of fine-grained sediment gravity-flow deposits(FGSGFD)are discussed,and future research prospects are clarified.In addition to the traditionally recognized low-density turbidity current and muddy debris flow,wave-enhanced gravity flow,low-density muddy hyperpycnal flow,and hypopycnal plumes can all form widely distributed FGSGFD.At the same time,the evolution of FGSGF during transportation can result in transitional and hybrid gravity-flow deposits.The combination of multiple triggering mechanisms promotes the widespread develop-ment of FGSGFD,without temporal and spatial limitations.Different types and concentrations of clay minerals,organic matters,and organo-clay complexes are the keys to controlling the flow transformation of FGSGF from low-concentration turbidity currents to high-concentration muddy debris flows.Further study is needed on the interaction mechanism of FGSGF caused by different initiations,the evolution of FGSGF with the effect of organic-inorganic synergy,and the controlling factors of the distribution pat-terns of FGSGFD.The study of FGSGFD can shed some new light on the formation of widely developed thin-bedded siltstones within shales.At the same time,these insights may broaden the exploration scope of shale oil and gas,which have important geological significances for unconventional shale oil and gas.展开更多
The types,evolution processes,formation mechanisms,and depositional models of deep-water gravity flow deposits in a lacustrine rift basin are studied through core observation and systematic analysis.Massive transport ...The types,evolution processes,formation mechanisms,and depositional models of deep-water gravity flow deposits in a lacustrine rift basin are studied through core observation and systematic analysis.Massive transport of slide and slump,fluid transport of debris flow and turbidity currents are driven by gravity in deep-water lacustrine environment.The transformation between debris flow and turbidity current,and the transformation of turbidity current between supercritical and subcritical conditions are the main dynamic mechanisms of gravity flow deposits in a lake basin.The erosion of supercritical turbidity current controls the formation of gravity-flow channel.Debris flow deposition gives rise to tongue shape lobe rather than channel.Deep-water gravity flow deposits are of two origins,intrabasinal and extrabasinal.Intrabasinal gravity flow deposits occur as single tongue-shape lobe or fan of stacking multiple lobes.Extrabasinal gravity-flow deposits occur as sublacustrine fan with channel or single channel sand body.However,the nearshore subaqueous fan is characterized by fan of stacking multiple tongue shape lobes without channel.The differential diagenesis caused by differentiation in the nearshore subaqueous fan facies belt results in the formation of diagenetic trap.The extrabasinal gravity flow deposits are one of the important reasons for the abundant deep-water sand bodies in a lake basin.Slide mass-transport deposits form a very important type of lithologic trap near the delta front often ignored.The fine-grained sediment caused by flow transformation is the potential"sweet spot"of shale oil and gas.展开更多
基金funded by the Strategic Cooperation Technology Projects of China National Petroleum Corporation(CNPC)China University of Petroleum(Beijing)(Grant No.ZLZX2020-02)the National Natural Science Foundation of China(Grant No.42272110)。
文摘Lacustrine gravity-flow deposits have enormous hydrocarbon potential.However,their depositional architecture has long been considered very complicated and is controlled by various factors,making petroleum exploration and development highly challenging.The influence of palaeogeomorphology on the extent and formation mechanisms of lacustrine gravity-flow deposits remains poorly understood.This study uses 3D seismic data,well-log data,and core data to characterize the palaeogeomorphology and depositional architecture of the lacustrine gravity-flow deposit of the Yanchang Formation in the Ordos Basin,while analyzing the influence of palaeogeomorphology on the architecture,distribution,and evolution of lacustrine gravity-flow deposit systems.The results showed that three palaeogeomorphologic units—shelf,slope,and basin floor—developed in the basin.Gravity-flow deposits can be further divided into channel and lobe systems.Gravity-flow channel systems have developed in the upper slope area,which include three types of architectural elements:confined channels,unconfined channels,and levee-overbank.As the transport distance of gravity flow increases,the erosion ability of gravity flow weakens,resulting in the terrain formed by gravity flow erosion gradually weakening the constraint on sediment transport.Consequently,gravity-driven flow pathways shift from linear,confined channels to curved,unconfined channels,finally leading to the development of numerous distributary channels.In the lower slope area,gravity flow sediments distribute rapidly and accumulate to form lobes after encountering slope breaks,due to the decrease of dynamics,including three types of architectural elements:distributary channels,lobe axis and lobe fringe.These lobes are tongue-shaped and fan-shaped on the plane.A series of lobes are superimposed and form a lobe complex set.These lobe complex sets are distributed in a branch-like manner.There are many branch-shaped low-bend amplitude channels inside the lobe complex set.Palaeogeomorphology plays an important role in controlling the spatial distribution of depositional architecture.As the slope gradient increases,the influence of slope break on sediment gravity flow weakens,leading to a delay of the sediment gravity flow slumping to the basin bottom.Additionally,the extension length of the channel system on the slope increases.Furthermore,the extension length of the lobes toward the center of the basin also increases.This work improves the fundamental understanding of the depositional architecture of lacustrine gravity-flow deposits and may help enhance sand prediction for the same type deposit reservoirs.
基金supported by National Natural Science Foundation of China(Grant Nos.42072126,42372139)the Natural Science Foundation of Sichuan Province(Grant Nos.2022NSFSC0990).
文摘Fine-grained sediments are widely distributed and constitute the most abundant component in sedi-mentary systems,thus the research on their genesis and distribution is of great significance.In recent years,fine-grained sediment gravity-flows(FGSGF)have been recognized as an important transportation and depositional mechanism for accumulating thick successions of fine-grained sediments.Through a comprehensive review and synthesis of global research on FGSGF deposition,the characteristics,depositional mechanisms,and distribution patterns of fine-grained sediment gravity-flow deposits(FGSGFD)are discussed,and future research prospects are clarified.In addition to the traditionally recognized low-density turbidity current and muddy debris flow,wave-enhanced gravity flow,low-density muddy hyperpycnal flow,and hypopycnal plumes can all form widely distributed FGSGFD.At the same time,the evolution of FGSGF during transportation can result in transitional and hybrid gravity-flow deposits.The combination of multiple triggering mechanisms promotes the widespread develop-ment of FGSGFD,without temporal and spatial limitations.Different types and concentrations of clay minerals,organic matters,and organo-clay complexes are the keys to controlling the flow transformation of FGSGF from low-concentration turbidity currents to high-concentration muddy debris flows.Further study is needed on the interaction mechanism of FGSGF caused by different initiations,the evolution of FGSGF with the effect of organic-inorganic synergy,and the controlling factors of the distribution pat-terns of FGSGFD.The study of FGSGFD can shed some new light on the formation of widely developed thin-bedded siltstones within shales.At the same time,these insights may broaden the exploration scope of shale oil and gas,which have important geological significances for unconventional shale oil and gas.
基金Supported by the National Natural Science Foundation of China(41802127,U1762217)China National Science and Technology Major Project(2016ZX05006-003)。
文摘The types,evolution processes,formation mechanisms,and depositional models of deep-water gravity flow deposits in a lacustrine rift basin are studied through core observation and systematic analysis.Massive transport of slide and slump,fluid transport of debris flow and turbidity currents are driven by gravity in deep-water lacustrine environment.The transformation between debris flow and turbidity current,and the transformation of turbidity current between supercritical and subcritical conditions are the main dynamic mechanisms of gravity flow deposits in a lake basin.The erosion of supercritical turbidity current controls the formation of gravity-flow channel.Debris flow deposition gives rise to tongue shape lobe rather than channel.Deep-water gravity flow deposits are of two origins,intrabasinal and extrabasinal.Intrabasinal gravity flow deposits occur as single tongue-shape lobe or fan of stacking multiple lobes.Extrabasinal gravity-flow deposits occur as sublacustrine fan with channel or single channel sand body.However,the nearshore subaqueous fan is characterized by fan of stacking multiple tongue shape lobes without channel.The differential diagenesis caused by differentiation in the nearshore subaqueous fan facies belt results in the formation of diagenetic trap.The extrabasinal gravity flow deposits are one of the important reasons for the abundant deep-water sand bodies in a lake basin.Slide mass-transport deposits form a very important type of lithologic trap near the delta front often ignored.The fine-grained sediment caused by flow transformation is the potential"sweet spot"of shale oil and gas.
