Deep limestone aquifers are potential CO2 storage sites, but CO2-saturated brine reacts with the carbonate rock, changing its transport and storage properties. This study provided a preliminary investigation of the optimal injection rate of CO2-saturated brine in carbonate rocks. Indiana limestone cores were subjected to CO2-saturated brine injection at varied rates using an HPHT coreflooding setup with X-ray CT monitoring. The samples were characterized pre- and post-treatment in terms of porosity and pore size distribution using a gas porosimeter and NMR T2 measurements. Moreover, the reaction was evaluated by measuring the aqueous effluent calcium ions concentration as a function of throughput using ICP-OES analysis. A high-resolution micro-CT scan was used to capture the dissolution post-treatments and characterize the wormhole's size and patterns. Results showed that the wormholes broke through to the sample exit face after injecting 160, 48, and 36 pore volumes at 0.5, 1, and 2 cm3/min, respectively thereby revealing the importance of injection velocity. The ICP-OES analysis revealed that a larger dissolution rate was achieved at 2 cm3/min, which explained the fast wormhole propagation. An increase in rock porosity and the pore-size distributions was observed after coreflooding on all samples with minimum precipitation, as concluded from the NMR T2 relaxation time. A universal optimum Damköhler number can be obtained that enables calculating the optimum injection rate of CO2-saturated brine at different rock and fluid conditions. We speculated that the optimum Damköhler number could be different from the value of 0.29 proposed by Fredd and Fogler (1998). This study provides a preliminary understanding of the optimal CO2-saturated brine injection velocity that has an application for CO2 storage, water alternating gas (WAG) operations, and acid stimulation of carbonate formations.

中文翻译：

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考虑虫洞传播效率的碳酸盐中 CO2 饱和盐水反应性运移的原位研究


深层石灰岩含水层是潜在的 CO2 储存场所，但 CO2 饱和的盐水会与碳酸盐岩发生反应，改变其运输和储存特性。本研究初步研究了碳酸盐岩中 CO2 饱和盐水的最佳注入速率。使用带有 X 射线 CT 监测的 HPHT 岩心驱装置，以不同速率对印第安纳州石灰石岩芯进行 CO2 饱和盐水注入。使用气体孔隙度计和 NMR T2 测量，根据孔隙率和孔径分布对样品进行处理前后的表征。此外，通过使用 ICP-OES 分析测量水流出物钙离子浓度与通量的函数关系来评估反应。高分辨率显微 CT 扫描用于捕获处理后的溶解并表征虫洞的大小和模式。结果表明，在分别以 0.5、1 和 2 cm3/min 的速度进样 160、48 和 36 个孔体积后，虫孔突破到样品出口面，从而揭示了进样速度的重要性。ICP-OES 分析显示，在 2 cm3/min 时实现了更大的溶出速率，这解释了虫洞的快速传播。从 NMR T2 弛豫时间得出结论，在所有降水最少的样品上，岩心驱后观察到岩石孔隙度和孔径分布增加。可以获得一个通用的最优 Damköhler 数，该数可以计算不同岩石和流体条件下 CO2 饱和盐水的最佳注入速率。我们推测最佳 Damköhler 数可能与 Fredd 和 Fogler （1998） 提出的 0.29 值不同。 本研究初步了解了最佳 CO2 饱和盐水注入速度，该速度可用于 CO2 储存、水交替气体 （WAG） 操作和碳酸盐形成的酸增产。