Browsing by Subject "flux"
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Item A Climatology of the Arctic on Mid-Tropospheric Temperature Regulation(2014-06-24) Anthony, Jeremy PatrickThe Arctic is a unique and complex environment. Many factors play a role in determining the long-term climate of the Arctic, including mesoscale weather systems and many complex ice-albedo feedback mechanisms. Previous studies determined using real observations that although 500 hPa temperatures reach -45? by mid-November, temperatures very rarely drop below, despite a total loss of incoming solar radiation. This temperature value at 500 hPa follows moist-adiabatically to the surface value of approximately -2?, which is the freezing point of high-latitude sea water. Sea ice data was examined using satellite and model data to paint a picture of the environment during three distinct periods in history: the last glacial maximum (twenty-one thousand years ago), the mid-Holocene (six-thousand years ago), and the 20th century. Areal September minimum sea ice extent has reached record lows annually since 2007. Vertical temperature profiles created with CCSM4 model data during these three eras show the atmosphere becoming more moist-adiabatic at high latitudes over time. Saturation potential vorticity allows us to assess the convective environment, and it shows that the Arctic is becoming more tropical over time. Analysis of areal extent where temperatures fall below -45? at 500 hPa shows this to be an extremely rare occurrence, and temperatures never fall below -47.5?, except for very rare occurrences during the last glacial maximum. Transient eddy heat flux is increasing at higher latitudes, and the warm half of a cyclone contains convection (as seen in saturation potential vorticity). In this paper, we present several lines of evidence supporting a role for intermittent convection in maintaining mid-tropospheric temperatures across climate states of the past twenty-one thousand years.Item Characterization of sediment movement in tidal creeks adjacent to the gulf intracoastal waterway at Aransas National Wildlife Refuge, Austwell, TX: study of natural factors and effects of barge-induced drawdown currents(Texas A&M University, 2005-08-29) Allison, John BryanThe coastal wetlands at Aransas National Wildlife Refuge near Austwell, Texas, support the last migrating population of whooping cranes during the winter months (October through April). With a population currently at 216 individuals, these are the rarest cranes in the world. The wetlands in which they winter are a part of the San Antonio Bay system, a bay that receives constant fresh water flow from the Guadalupe River. Currently there is a plan for using water diverted from the Guadalupe River just before it enters San Antonio Bay as a water supply for the greater San Antonio metropolitan area located 200 km to the northwest. The Guadalupe River delivers nutrients and sediment into the estuary along with fresh water. Because of the importance of sediment within a tidal wetland ecosystem, it is imperative to understand the sediment budget and underlying forces that drive it if one is to ultimately grasp how this ecosystem functions. To document natural and anthropogenic factors exerting control over sediment movement in this system, three sites on tidal creeks near the boundary between marsh and bay were chosen. The Gulf Intracoastal Waterwayparallels the marsh edge. Over six, non-consecutive weeks water level and velocity were automatically monitored in the tidal creeks. Automated water samplers extracted water samples that were analyzed for suspended sediment. In addition, bedload traps were deployed in one creek to monitor sediment movement along the channel bottom. Inflow exceeded outflow during the study. As a result there was a net influx of suspended sediments into the marsh. Bedload material also moves with current direction, and it appears to move in response to barge induced outflow currents. Barges passing on the Gulf Intracoastal Waterway exert influence on water level, flow direction, and velocity within tidal creeks. Natural factors such as winds, tides, and freshwater input from upland runoff or river discharge also impact suspended and bedload sediments.Item Foolproof completions for high rate production wells(2009-05-15) Tosic, SlavkoOperators, especially those managing production from deepwater reservoirs, are striving to produce hydrocarbons at higher and higher rates without exposing the wells to completion failure risk. To avoid screen failures, recent studies have favored gravel pack (GP) and high rate water pack (HRWP) completions over high-permeability fracturing (HPF), known in the vernacular as a frac&pack (FP) for very high rate wells. While a properly designed GP completion may prevent sand production, it does not stop formation fines migration, and, over time, fines accumulation in the GP will lead to increasing completion skin. Although, and not always, the skin can be removed by acidizing, it is not practical to perform repeated acid treatments on deepwater wells, particularly those with subsea wellheads, and the alternative has been to subject the completion to increasingly high drawdown, accepting a high skin effect. A far better solution is to use a HPF completion. Of course the execution of a successful HPF is not a trivial exercise, and frequently, there is a steep learning curve for such a practice. This work explains the importance to HPF completions of the well trajectory through the interval to be hydraulically fractured, for production, not execution, reasons. A new model quantifies the effect of the well inclination on the connectivity between the fracture and the well via perforations. Guidelines based on the maximum target production rate, including forecasts of multiphase flow, are provided to size the HPF completion to avoid common completion failures that may result from high fluid rate and/or fines movement. Skin model will be developed for both vertical and deviated wells. Once the HPF is properly designed and executed, the operators should end up with a long term low skin good completion quality well. The well will be safely produced at the maximum flow rates, with no need for well surveillance and monitoring.