In order to comprehend the scale and connectivity of sandbodies in late oilfield development, it is imperative to conduct a detailed characterization of fluvial sandbodies in the upper Guantao Formation of Gudong oilfield. Through comprehensive analysis of core, well logging, and seismic data, the sedimentary characteristics of braided river and meandering river were determined under the control of dense well array. The results indicate that the upper Guantao Formation has undergone a sedimentary evolution process from braided river to meandering river. The lower Guantao Formation exhibits braided fluvial reservoir with braid bar, braid channel, and overbank sand microfacies, while the upper Guantao Formation features meandering fluvial reservoir with microfacies types such as point bar, abandoned channel, crevasse splay, and floodplain. By conducting core-log calibration analysis, the logging response characteristics and sandbody development laws of braided and meandering rivers were determined. The channel sandbody of a braided river is cut and overlapped in multiple stages while being distributed across multiple branches on a plane. On the other hand, the meandering fluvial channel sandbody develops in isolation but forms strips on a plane. Under the control of dense well array, we have quantitatively determined the scale of sandbody development for both braided and meandering rivers. Additionally, the relationship between sandbody thickness and width for different river types were established which holds significant guiding significance for identifying sandbody connectivity and 3D geological modeling.