► Increasing injectivity of saline aquifers affects CO2 long-term storage. ► Vertical hydraulic fractures decrease long-term trapping of CO2 in aquifers. ► Fraction of long-term trapped CO2 is a ...function of stimulated aquifer’s stress regime. ► Non-Darcy flow inside the fracture decreases injectivity of stimulated saline aquifers. ► Water injection into stimulated saline aquifer improves residual trapping of CO2.
Stimulation techniques, primarily as hydraulic fracturing, can contribute to improve practical storage capacity of low-permeable saline aquifers by increasing injectivity. Since the shape of the CO2 plume in the injection period can affect its subsequent migration, impact of hydraulic fracturing on post-injection plume migration should be investigated to assess CO2 long-term trapping in stimulated saline aquifers. Compositional reservoir simulation results, based on a case study of Rose Run sandstone aquifer in Ohio River Valley, show the important role of methods for increasing near wellbore injectivity on CO2 plume dynamics. Significant tradeoff between enhancing injectivity and long-term trapping of carbon dioxide in hydraulically fractured saline aquifers in normal faulting regime is proven by analysis of parameters controlling CO2 storage in saline aquifers such as gravity number. In addition, we discuss effects of the aquifer stress regime, fracture properties, and injection of water on immobilization of CO2 by residual and solubility trapping inside the stimulated saline aquifers. Finally, we show that non-Darcy flow effects inside the fracture could reduce injectivity of the stimulated saline aquifer by causing additional pressure drop inside the fracture.
Conditions have been studied for the determination of Sn by coupling of hydride generation and graphite furnace atomic absorption spectrometry. Sequestering and in situ concentration of Sn hydride in ...the graphite furnace requires just a single application of a long-term stable trapping reagent for automated analyses. In a systematic study it is shown that effective trapping of stannane is possible on graphite tubes or platforms coated with a carbide-forming element such as Zr, Nb, Ta, or W at trapping temperatures of 500 to 600°C. Trapping temperatures should not be higher than 600°C (the “critical temperature”) because otherwise at temperatures higher than 700°C errors in absorbance values could occur by an adsorptive “carry-over effect”. Signal stability and reproducibility are tested over more than 400 complete trapping and atomization cycles, and a precision of 2% is observed. Narrow peaks are obtained for all coatings except for Nb- and Ta-coated platforms where double peaks occur. Ir- or Pd/Ir-coated surfaces allow trapping of stannane at lower temperatures but the signal stability (especially in the case of Pd/Ir coating) is lower than with the carbide-forming element coatings. The highest sensitivity is found for Zr- and W-coated tubes with a characteristic mass of about 17 and 20 pg, respectively, and the calibration curves are linear up to 2 ng Sn on Zr-treated tubes (peak height) and 4 ng on Zr-coated platforms (integrated absorbance) using the 286.3 nm line. The detection limit is 25 pg for a 1 ml sample volume, and the reagent blank is still significant with the purest available chemicals. The method is tested by determination of Sn in low alloy steel samples.
