Changes

''Meandering rivers'' are different in that sand is restricted to a single channel and surrounded by fine-grained sediments (Figure 3d). Sand is concentrated mainly in the channel bottoms and point bars. A vertical sequence through such a channel system frequently has an upward-fining character, starting from the channel lag at the bottom and grading upward into deposits of the adjacent levee and floodplain. Individual meander belts are built of cross-cutting and stacked individual upward-fining sequences often separated laterally by meander loop cutoffs and clay plugs. Multiple meander belts are built by abandonment of an entire river segment (''avulsion'') and by establishment of a new section in another position on the floodplain.

''Meandering rivers'' are different in that sand is restricted to a single channel and surrounded by fine-grained sediments (Figure 3d). Sand is concentrated mainly in the channel bottoms and point bars. A vertical sequence through such a channel system frequently has an upward-fining character, starting from the channel lag at the bottom and grading upward into deposits of the adjacent levee and floodplain. Individual meander belts are built of cross-cutting and stacked individual upward-fining sequences often separated laterally by meander loop cutoffs and clay plugs. Multiple meander belts are built by abandonment of an entire river segment (''avulsion'') and by establishment of a new section in another position on the floodplain.

Gamma ray, SP, and resistivity logs through braided channel complexes generally have a blocky character, whereas individual meandering channels have an upward-fining signature except where stacked and cross-cut, where they may exhibit more complex wireline log signatures.

[[Basic open hole tools#Gamma ray|Gamma ray]], [[Basic open hole tools#Spontaneous potential|SP]], and [[Basic open hole tools#Resistivity|resistivity]] logs through braided channel complexes generally have a blocky character, whereas individual meandering channels have an upward-fining signature except where stacked and cross-cut, where they may exhibit more complex wireline log signatures.

The upward-fining character of fluvial channels tends to produce sandstone bodies that have their greatest permeability at the base of the body. However, the common stacking and cross-cutting of channels in both braided and meandering river deposits often produces a complex spatial distribution of permeability within the braided or meander belt. Preferred permeability pathways, and consequently, fluid flow, can be expected to follow the paleochannel direction.<ref name=pt06r104>Qiu, Yinan, 1984, Depositional model, heterogeneous characteristics, and waterflood performance of sandstone reservoirs in a lake basin case study of oilfields, eastern China: Proceedings of the 11th World Petroleum Congress, v. 3, p. 113–125.</ref>

The upward-fining character of fluvial channels tends to produce sandstone bodies that have their greatest permeability at the base of the body. However, the common stacking and cross-cutting of channels in both braided and meandering river deposits often produces a complex spatial distribution of permeability within the braided or meander belt. Preferred permeability pathways, and consequently, fluid flow, can be expected to follow the paleochannel direction.<ref name=pt06r104>Qiu, Yinan, 1984, Depositional model, heterogeneous characteristics, and waterflood performance of sandstone reservoirs in a lake basin case study of oilfields, eastern China: Proceedings of the 11th World Petroleum Congress, v. 3, p. 113–125.</ref>