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首页> 外文期刊>Environmental Science & Technology >Alterations of Fractures in Carbonate Rocks by CO_2-Acidified Brines
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Alterations of Fractures in Carbonate Rocks by CO_2-Acidified Brines

机译：CO_2-酸化卤水对碳酸盐岩裂缝的影响

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摘要

Fractures in geological formations may enable migration of environmentally relevant fluids, as in leakage of CO_2 through caprocks in geologic carbon sequestration. We investigated geochemically induced alterations of fracture geometry in Indiana Limestone specimens. Experiments were the first of their kind, with periodic high-resolution imaging using X-ray computed tomography (xCT) scanning while maintaining high pore pressure (100 bar). We studied two CO_2-acidified brines having the same pH (3.3) and comparable thermodynamic disequilibrium but different equilibrated pressures of CO_2 (P_(CO_2) values of 12 and 77 bar). High-P_(CO_2) brine has a faster calcite dissolution kinetic rate because of the accelerating effect of carbonic acid. Contrary to expectations, dissolution extents were comparable in the two experiments. However, progressive xCT images revealed extensive channelization for high P_(CO_2), explained by strong positive feedback between ongoing flow and reaction. The pronounced channel increasingly directed flow to a small region of the fracture, which explains why the overall dissolution was lower than expected. Despite this, flow simulations revealed large increases in permeability in the high-P_(CO_2) experiment. This study shows that the permeability evolution of dissolving fractures will be larger for faster-reacting fluids. The overall mechanism is not because more rock dissolves, as would be commonly assumed, but because of accelerated fracture channelization.
机译：地质构造中的裂缝可能使环境相关的流体迁移，例如地质碳固存中二氧化碳通过盖层泄漏的情况。我们调查了印第安纳州石灰岩标本中地球化学诱导的裂缝几何形状的变化。实验是第一个此类实验，使用X射线计算机断层扫描（xCT）扫描进行定期高分辨率成像，同时保持较高的孔隙压力（100 bar）。我们研究了两种具有相同pH（3.3）和可比较的热力学不平衡但具有不同平衡压力的CO_2（P_（CO_2）值为12和77 bar）的CO_2酸化盐水。高P_（CO_2）盐水由于碳酸的加速作用而具有更快的方解石溶解动力学速率。与预期相反，在两个实验中溶出度是可比较的。然而，渐进的xCT图像显示了高P_（CO_2）的广泛通道化，这可以通过正在进行的流动和反应之间强烈的正反馈来解释。明显的通道越来越多地将流量导向裂缝的一小部分，这解释了为什么总溶出度低于预期。尽管如此，流动模拟显示在高P_（CO_2）实验中渗透率大大增加。这项研究表明，对于反应速度更快的流体，溶解裂缝的渗透率演化会更大。总体机制并非如通常所认为的那样，是因为更多的岩石溶解了，而是由于加速了裂缝的通道化。

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  • 来源
    《Environmental Science & Technology》 |2015年第16期|10226-10234|共9页
  • 作者

    Hang Deng; Jeffrey P. Fitts; Dustin Crandall; Dustin McIntyre; Catherine A. Peters;

  • 作者单位

    Department of Civil and Environmental Engineering, Princeton University, Princeton, New Jersey 08544, United States;

    Department of Civil and Environmental Engineering, Princeton University, Princeton, New Jersey 08544, United States;

    National Energy Technology Laboratory, Morgantown, West Virginia 26507, United States;

    National Energy Technology Laboratory, Morgantown, West Virginia 26507, United States;

    Department of Civil and Environmental Engineering, Princeton University, Princeton, New Jersey 08544, United States;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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