DETERMINING THE PERMEABILITY OF BRAIDED RIVER DEPOSITS FROM THE SAGAVANIRKTOK RIVER, ALASKA: A MODERN ANALOG FOR GLACIAL OUTWASH AQUIFERS AND PETROLEUM RESERVOIRS

Modern braided river deposits may serve as analogs for developing models of glacial outwash aquifers and petroleum reservoirs. The purpose of this study was to determine the range of permeability in modern braided river deposits within a point bar aquifer on the Sagavanirktok River near Deadhorse, AK. Three hydrofacies were identified from grain size distribution analysis, ground penetrating radar lines, and trenches: 1) open-framework gravel; 2) sand, and; 3) sand and gravel. Permeabilities of individual hydrofacies were determined by air permeameter measurements of cored samples and constant head permeameter tests of disturbed samples. Permeabilities for sand and sand and gravel hydrofacies from air permeameter tests were between 2 – 3 darcies and 1 – 20 darcies, respectively. All air permeameter measurements for the open-framework gravels were 20 darcies, the maximum value the air permeameter was calibrated to read. It is likely therefore this value is not valid, but does provide a minimum estimate of the open-framework gravel’s permeability. Permeability results from constant head permeameter tests ranged between 150 – 180 darcies for open-framework gravels and 20 – 30 darcies for sands. Bulk permeability of the aquifer materials determined from pump test analyses and numerical inverse groundwater modeling ranged between 1,100 – 4,300 darcies (for pump test analyses) and 40 – 500 darcies (for inverse groundwater models). The permeabilities of the sand and sand and gravel hydrofacies are similar to those documented in other studies. The permeabilities of open-framework gravels are 1 – 2 orders of magnitude lower than results reported in similar studies of glacial outwash deposits containing open-framework gravels. There was significant variation in the estimates of permeabilities of these sediments depending upon the scale and technique used. This indicates that there is a need for estimates of permeability using multiple techniques to understand uncertainty and issues of scale.