Suchergebnisse

The injection of supercritical carbon dioxide (CO2) in deep saline aquifers leads to the formation of a CO2 rich phase plume that tends to float over the resident brine. As pressure builds up, CO2 density will increase because of its high compressibility. Current analytical solutions do not account for CO2 compressibility and consider a volumetric injection rate that is uniformly distributed along the whole thickness of the aquifer, which is unrealistic. Furthermore, the slope of the CO2 pressure with respect to the logarithm of distance obtained from these solutions differs from that of numerical solutions. We develop a semianalytical solution for the CO2 plume geometry and fluid pressure evolution, accounting for CO2 compressibility and buoyancy effects in the injection well, so CO2 is not uniformly injected along the aquifer thickness. We formulate the problem in terms of a CO2 potential that facilitates solution in horizontal layers, with which we discretize the aquifer. Capillary pressure is considered at the interface between the CO2 rich phase and the aqueous phase. When a prescribed CO2 mass flow rate is injected, CO2 advances initially through the top portion of the aquifer. As CO2 is being injected, the CO2 plume advances not only laterally, but also vertically downwards. However, the CO2 plume does not necessarily occupy the whole thickness of the aquifer. We found that even in the cases in which the CO2 plume reaches the bottom of the aquifer, most of the injected CO2 enters the aquifer through the layers at the top. Both CO2 plume position and fluid pressure compare well with numerical simulations. This solution permits quick evaluations of the CO2 plume position and fluid pressure distribution when injecting supercritical CO2 in a deep saline aquifer. © 2013 Springer Science+Business Media Dordrecht. ; This work has been funded by Fundación Ciudad de la Energía (Spanish Government) (www.ciuden.es) and 35 by the European Union through the "European Energy Programme for Recovery" and the Compostilla OXYCFB300 project. We also want to acknowledge the financial support received from the 'MUSTANG' (www.co2mustang.eu) and 'PANACEA' (www.panacea-co2.org) projects (from the European Community's Seventh Framework Programme FP7/2007-2013 under grant agreements nº 227286 and nº 282900, respectively). ; Peer Reviewed

Accurate wind speed estimates at turbine hub height are critical for wind farm operational purposes, such as forecasting and grid operation, but also for wind energy assessments at regional scales. Power law models have widely been used for vertical wind speed profiles due to their simplicity and suitability for many applications over diverse geographic regions. The power law requires estimation of a wind shear coefficient, α, linking the surface wind speed to winds at higher altitudes. Prior studies have mostly adopted simplified models for α, ranging from a single constant, to a site-specific constant in time value. In this work we (i) develop a new model for α which is able to capture hourly variability across a range of geographic/topographic features; (ii) quantify its improved skill compared to prior studies; and (iii) demonstrate implications for wind energy estimates over a large geographical area. To achieve this we use long-term high-resolution simulations by the Weather Research and Forecasting model, as well as met-mast and radiosonde observations of vertical profiles of wind speed and other atmospheric properties. The study focuses on Saudi Arabia, an emerging country with ambitious renewable energy plans, and is part of a bigger effort supported by the Saudi Arabian government to characterize wind energy resources over the country. Results from this study indicate that the proposed model outperforms prior formulations of α, with a domain average reduction of the wind speed RMSE of 23–33%. Further, we show how these improved estimates impact assessments of wind energy potential and associated wind farm siting. ; This publication is based upon work supported by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No: OSR-CRG 7 2018-3742.2. The authors thank the King Abdullah City for Atomic and Renewable Energy (K.A.CARE) for providing the wind speed observational data. HRES-ECMWF operational analysis data were downloaded from the ECMWF data portal (https://www.ecmwf.int/en/forecasts/datasets/set-i.) through the KAUST ECMWF licence.