The 270 km long section of the Upper Yellow River at the First Great Bend is comprised of single channel and multiple channel systems that alternate among anastomosing, anabranching, meandering and braided reaches. Th...The 270 km long section of the Upper Yellow River at the First Great Bend is comprised of single channel and multiple channel systems that alternate among anastomosing, anabranching, meandering and braided reaches. The sequence of downstream pattern changes is characterized as： anastomosing-anabranching, anabranching-meandering, meandering-braided and braided-meandering. Remote sensing images, DEM data and field investigations are used to assess ahd interpret controls on these reach transitions. Channel slope and bed sediment size are key determinants of transitions in channel planform. Anas- tomosing reaches have a relatively high bed slope （0.86‰） and coarser sediment bed material （d50 = 3.5 mm）. In contrast, meandering reaches have a low slope （0.30‰） and fine sediment bed material （d50 = 0.036 mm）. The transition from a meandering to braided pattern is characterized by an increase in channel width-depth ratio, indicating the important role of bank strength （i.e. cohesive versus non-cohesive versus channel boundaries）. Interestingly, the braided-meandering and meandering-braided transitions are coincident with variable flow inputs from tributary rivers （Baihe and Heihe rivers respectively）. Theoretical analysis of the meandering-braided transition highlights the key control of channel width-depth ratio as a determinant of channel planform.展开更多
Subaqueous distributary channel sandbodies within delta fronts are crucial reservoirs in continental petroliferous basins.Understanding the spatiotemporal transition of river patterns in these channels is essential fo...Subaqueous distributary channel sandbodies within delta fronts are crucial reservoirs in continental petroliferous basins.Understanding the spatiotemporal transition of river patterns in these channels is essential for accurate evaluation and prediction of oil and gas reservoirs,as well as for providing direct evidence of basin evolution.In the Yabus Formation of the Sag A of Melut Basin,a comprehensive analysis involving sequence division,sedimentary characteristics,seismic facies,highresolution reservoir inversion,and sand body distribution revealed significant insights.During the Yabus Formation deposition,three intermediate base-level cycles were identified,each showing transition phenomena in the river patterns of subaqueous distributary channels within the delta front.Clear identification criteria for different river patterns were established.Braided subaqueous distributary channels exhibited dominant vertical accretion,high sand content,significant sandstone thickness,and continuousstrong amplitude seismic reflections.While the braidedmeandering transition pattern showed a combination of vertical and lateral accretion,medium sand content,moderate sandstone thickness,and medium continuousmedium strong amplitude seismic reflections.Meandering subaqueous distributary channels were characterized by lateral accretion,low sand content,minimal sandstone thickness,weak continuous-weak amplitude seismic reflections,and mud-rich inversion features.The primary control factor influencing the transition of river patterns in these channels was identified as the long-term base-level cycle,shaped by paleotopography and sediment supply.Braided subaqueous distributary channels emerged as the main exploration interval for structural prospects,serving as lateral high-speed migration pathways.Dendritic braided and meandering transition intervals were deemed favorable for both structure-lithologic prospects and the expansion of new exploration fields and layers.展开更多
基金International Science ＆ Technology Cooperation Program of China, No.2011DFA20820 No.2011DFG93160+1 种基金 Tsinghua University, No.20121080027 National Natural Science Foundation of China, No.51209010 Acknowledgments We would like to thank Professor Huang Heqing for his helpful guidance in finalizing the paper.
文摘The 270 km long section of the Upper Yellow River at the First Great Bend is comprised of single channel and multiple channel systems that alternate among anastomosing, anabranching, meandering and braided reaches. The sequence of downstream pattern changes is characterized as： anastomosing-anabranching, anabranching-meandering, meandering-braided and braided-meandering. Remote sensing images, DEM data and field investigations are used to assess ahd interpret controls on these reach transitions. Channel slope and bed sediment size are key determinants of transitions in channel planform. Anas- tomosing reaches have a relatively high bed slope （0.86‰） and coarser sediment bed material （d50 = 3.5 mm）. In contrast, meandering reaches have a low slope （0.30‰） and fine sediment bed material （d50 = 0.036 mm）. The transition from a meandering to braided pattern is characterized by an increase in channel width-depth ratio, indicating the important role of bank strength （i.e. cohesive versus non-cohesive versus channel boundaries）. Interestingly, the braided-meandering and meandering-braided transitions are coincident with variable flow inputs from tributary rivers （Baihe and Heihe rivers respectively）. Theoretical analysis of the meandering-braided transition highlights the key control of channel width-depth ratio as a determinant of channel planform.
文摘Subaqueous distributary channel sandbodies within delta fronts are crucial reservoirs in continental petroliferous basins.Understanding the spatiotemporal transition of river patterns in these channels is essential for accurate evaluation and prediction of oil and gas reservoirs,as well as for providing direct evidence of basin evolution.In the Yabus Formation of the Sag A of Melut Basin,a comprehensive analysis involving sequence division,sedimentary characteristics,seismic facies,highresolution reservoir inversion,and sand body distribution revealed significant insights.During the Yabus Formation deposition,three intermediate base-level cycles were identified,each showing transition phenomena in the river patterns of subaqueous distributary channels within the delta front.Clear identification criteria for different river patterns were established.Braided subaqueous distributary channels exhibited dominant vertical accretion,high sand content,significant sandstone thickness,and continuousstrong amplitude seismic reflections.While the braidedmeandering transition pattern showed a combination of vertical and lateral accretion,medium sand content,moderate sandstone thickness,and medium continuousmedium strong amplitude seismic reflections.Meandering subaqueous distributary channels were characterized by lateral accretion,low sand content,minimal sandstone thickness,weak continuous-weak amplitude seismic reflections,and mud-rich inversion features.The primary control factor influencing the transition of river patterns in these channels was identified as the long-term base-level cycle,shaped by paleotopography and sediment supply.Braided subaqueous distributary channels emerged as the main exploration interval for structural prospects,serving as lateral high-speed migration pathways.Dendritic braided and meandering transition intervals were deemed favorable for both structure-lithologic prospects and the expansion of new exploration fields and layers.
