Evaluation of Permeability in the Unsaturated Zone at the Nevada Test Site Using Barometric Pressure Modeling

摘要

A total of 130 days of barometric pressure data were recorded at the Nevada Test Site emplacement holes U2fe, completed in Area 2 alluvium, and U19ac and U20ai, completed in volcanics on Pahute Mesa, for the purpose of evaluating unsaturated-zone permeability at those sites. All of the holes were partially cased and instrumented with high-precision quartz pressure gauges suspended on a wireline in the holes roughly 6 m from the surface. The casing was sealed to eliminate direct pressure communication with the atmosphere. Simultaneous surface and in-hole pressure data were sampled at half-hour intervals for periods between two and five weeks at each site. The data were interpreted using a non-linear least squares iterative procedure to fit either a single- or multi-layer half-space model to the observed in-hole pressure variations. The model included the effect of the partially cased hole intersecting the half-space, and assumed two-dimensional (radial and vertical) gas flow in the formation. The imposed surface boundary condition was the recorded surface barometric pressure. Layer thicknesses were based on well logs. 8 refs., 14 figs. (ERA citation 10:050053)