Study of Modern Gravelly Braided River Deposits with Special Reference to Spatial Variations in Porosity and Permeability

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9902894BridgeThe nature and origin of gravelly braided-river deposits will be studied, with specific emphasis on spatial variations in porosity and permeability. Channel-belt deposits will be studied in 3-D using closely spaced ground-penetrating radar profiles tied to trenches, cores and wireline logs. An innovative aspect of this study is that the river and sediment will be frozen during some of the sampling (being on the North Slope of Alaska), thus minimizing disturbance during coring, and enabling easy access to all parts of the channel belt. This sampling strategy will allow description of the 3-D variation of the different types and scales of stratification, grain-size distributions, porosity and permeability, and related geophysical properties of the deposits. Particular attention will be paid to zones of high permeability (open-framework gravels) and low permeability (muds). Interpretation of these patterns of deposition will be attempted using: (1) knowledge of the mode of channel cutting, migration and filling, obtainable from sequential aerial photographs, and; (2) inferences about the geometry, sediment textures and bed forms of the channel bed during major erosional-depositional events. An ultimate objective is construction of a detailed, 3-D depositional model for gravelly braided rivers that is a major improvement over existing models, particularly in the description of the large-scale stratification patterns. Also, prediction of porosity and permeability in relation to sedimentary facies is important for modeling of fluid flow through aquifers and hydrocarbon reservoirs in analogous ancient deposits. However, there is a critical lack of poroperm data from gravelly braided rivers to support such modeling. The results of a pilot study indicate that the objectives of this project can be realized.