Two new types of sandbars are found in distributary channels of the modern Ganjiang Delta,Poyang Lake,China,respectively named as branching-point bar(BPB) and merging-point bar(MPB).BPB is defined as sandbar formed at...Two new types of sandbars are found in distributary channels of the modern Ganjiang Delta,Poyang Lake,China,respectively named as branching-point bar(BPB) and merging-point bar(MPB).BPB is defined as sandbar formed at the branching point of a channel where one channel branches into two.MPB is defined as sandbar formed at the merging point of two channels.BPB results from current velocity decrease at the branching point.BPB,arrowhead-shaped and growing towards upstream through upstream accretion,can be divided into bar head,middle and tail.Bar head refers to the lower part of the bar below average low water level,submerges under water whether in rainy seasons or dry seasons,and no plants grow on it.Bar middle refers to the middle part of the bar between average low and average high water levels,and sparse plants grow on it.Bar tail refers to the upper part of the bar above average high water level,and plants grow densely on it.From bar head to bar tail,sediment becomes finer and sorting degree becomes poorer;plant fossils increase in number,and silting-mud layers increase both in number and thickness.Vertically BPB shows a fining-upward sequence.BPB can be classified into 3 types:baby BPB with only bar head,child BPB with bar head and middle,and adult BPB with bar head,middle and tail.Generally from the lower delta plain to upper delta plain,BPB becomes more and more mature.If a channel is suddenly abandoned,BPB at different stages may be preserved.MPB is very similar to BPB in depositional characteristics,and main differences lie in its origin and growth direction.Discovery of BPB and MPB has important implications in finding remaining oil in oilfields.Previously,geologists considered point bars on convex bank of meandering channels or longitudinal bars and transverse bars in the middle of braided channels as favorable locations for finding remaining oil.Our study shows such locations as branching points and merging points of channels are also significant because BPB and MPB develop at these locations.Remaining oil has been found at branching points of channels in Pubei Oilfield,Songliao Basin,Northeast China.展开更多
通过现代三角洲沉积的卫星照片可以获取并分析水下分流河道与河口坝的定量数据及其平面分布规律,丰富与完善储层地质知识库。以鄱阳湖三角洲为主要为研究对象,结合Wax Lake Delta现代沉积的卫星照片,对典型的朵状河控三角洲前缘水下分...通过现代三角洲沉积的卫星照片可以获取并分析水下分流河道与河口坝的定量数据及其平面分布规律,丰富与完善储层地质知识库。以鄱阳湖三角洲为主要为研究对象,结合Wax Lake Delta现代沉积的卫星照片,对典型的朵状河控三角洲前缘水下分流河道与河口坝的平面分布特征及其相互关系进行定性及定量研究。结果表明水下分流河道的分叉角度近50°,向湖盆方向宽度变窄(宽度降低0.72倍)、数量变多,呈发散叶脉状;单一的河口坝呈三角状和狭长心滩状,其中三角状河口坝发育在三角洲前缘下部,狭长心滩状河口坝位于三角洲前缘中上部,并且河口坝长度与宽度之间存在较好的线性关系。研究结果可以有效指导相似地下储层的精细微相研究。展开更多
文摘Two new types of sandbars are found in distributary channels of the modern Ganjiang Delta,Poyang Lake,China,respectively named as branching-point bar(BPB) and merging-point bar(MPB).BPB is defined as sandbar formed at the branching point of a channel where one channel branches into two.MPB is defined as sandbar formed at the merging point of two channels.BPB results from current velocity decrease at the branching point.BPB,arrowhead-shaped and growing towards upstream through upstream accretion,can be divided into bar head,middle and tail.Bar head refers to the lower part of the bar below average low water level,submerges under water whether in rainy seasons or dry seasons,and no plants grow on it.Bar middle refers to the middle part of the bar between average low and average high water levels,and sparse plants grow on it.Bar tail refers to the upper part of the bar above average high water level,and plants grow densely on it.From bar head to bar tail,sediment becomes finer and sorting degree becomes poorer;plant fossils increase in number,and silting-mud layers increase both in number and thickness.Vertically BPB shows a fining-upward sequence.BPB can be classified into 3 types:baby BPB with only bar head,child BPB with bar head and middle,and adult BPB with bar head,middle and tail.Generally from the lower delta plain to upper delta plain,BPB becomes more and more mature.If a channel is suddenly abandoned,BPB at different stages may be preserved.MPB is very similar to BPB in depositional characteristics,and main differences lie in its origin and growth direction.Discovery of BPB and MPB has important implications in finding remaining oil in oilfields.Previously,geologists considered point bars on convex bank of meandering channels or longitudinal bars and transverse bars in the middle of braided channels as favorable locations for finding remaining oil.Our study shows such locations as branching points and merging points of channels are also significant because BPB and MPB develop at these locations.Remaining oil has been found at branching points of channels in Pubei Oilfield,Songliao Basin,Northeast China.
文摘通过现代三角洲沉积的卫星照片可以获取并分析水下分流河道与河口坝的定量数据及其平面分布规律,丰富与完善储层地质知识库。以鄱阳湖三角洲为主要为研究对象,结合Wax Lake Delta现代沉积的卫星照片,对典型的朵状河控三角洲前缘水下分流河道与河口坝的平面分布特征及其相互关系进行定性及定量研究。结果表明水下分流河道的分叉角度近50°,向湖盆方向宽度变窄(宽度降低0.72倍)、数量变多,呈发散叶脉状;单一的河口坝呈三角状和狭长心滩状,其中三角状河口坝发育在三角洲前缘下部,狭长心滩状河口坝位于三角洲前缘中上部,并且河口坝长度与宽度之间存在较好的线性关系。研究结果可以有效指导相似地下储层的精细微相研究。
