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Experimental study of gravitational mixing of supercritical CO2
International Journal of Greenhouse Gas Control ( IF 3.9 ) Pub Date : 2018-02-25 , DOI: 10.1016/j.ijggc.2018.02.013
Dennis L. Newell , J. William Carey , Scott N. Backhaus , Peter Lichtner

CO2 injection into saline aquifers for sequestration will initially result in buoyant supercritical (sc)CO2 trapped beneath the caprock seal. During this period, there is risk of CO2 migration out of the reservoir along wellbore defects or fracture zones. Dissolution of the scCO2 plume into brine results in solubility trapping and reduces this risk, but based on diffusion alone, this mechanism could take thousands of years. Gravitational (density-induced) mixing of CO2-saturated brine is shown to significantly accelerate this process in computational studies, but few experimental efforts have confirmed the phenomenon. Here, constant-pressure, 3-dimensional bench-scale experiments used the mass of added water to quantify the mass transfer of scCO2 into water-saturated porous media at 40–90 °C and 20 MPa, with Rayleigh numbers from 2093 to 16256. Experiments exhibit a period of 7–35X enhancement in mass transfer rates over diffusion, interpreted as gravitational mixing. Convective CO2 flux ranges from 1.6 × 10−2 to 4.8 × 10−3 mol s−1 m−2 in the experiments. Results are used to benchmark a computational model using PFLOTRAN. Experiments show an early diffusive onset period that is shorter with rates much higher than predicted by models and observed in analog experiments. Both experiments and models show convective mixing periods and similar overall rates of CO2 mass transfer.



中文翻译:

超临界CO 2重力混合实验研究

将CO 2注入盐水层进行封存将首先导致浮力超临界(sc)CO 2被困在盖层密封之下。在此期间,存在CO 2沿井眼缺陷或裂缝带从储层中运出的风险。将scCO 2羽状物溶解到盐水中会导致溶解性捕获并降低这种风险,但是仅基于扩散,这种机制可能要花费数千年的时间。重力(密度引起的)CO 2混合在计算研究中,饱和盐水可以显着加速这一过程,但是很少有实验证明这一现象。在这里,恒压3维台式实验使用添加的水的质量来量化scCO 2在40–90°C和20 MPa下向水饱和的多孔介质中的质量转移,瑞利数为2093至16256实验表明,传质速率比扩散提高了7-35倍,这被解释为重力混合。对流CO 2通量范围为1.6×10 -2到4.8×10 -3 mol s -1  m -2在实验中。结果用于使用PFLOTRAN对计算模型进行基准测试。实验表明,早期扩散扩散期较短,发生率远高于模型预测和模拟实验中观察到的扩散期。实验和模型均显示了对流混合周期和相似的CO 2传质总速率。

更新日期:2018-02-25
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