During the CO geological sequestration in saline aquifers, salt precipitation issues can diminish reservoir injectivity and significantly escalate injection costs. Variations in the gas supply during injection can lead to fluctuations in CO injection rates. These abrupt changes in injection parameters can affect the distribution of reservoir pressures and brine migration behavior, subsequently influencing salt precipitation dynamics. This study employs a designed micromodel with representative geological boundary conditions to investigate salt precipitation behavior under variable injection conditions, and the experimental conditions are at atmospheric pressure and 50 °C. The flow rates of the CO injection flow rates range from 0.5 mL/min to 4 mL/min. The findings reveal that under variable injection conditions, changes in gas injection rates can induce fluctuations in the reservoir solution, leading to the formation of “wet salt barriers” characterized by clustered salt growth near the inlet. This phenomenon significantly impairs injectivity. When sufficient supplemental solution is introduced, most of the previously precipitated salt is initially dissolved, eventually reaching a dynamic equilibrium that restricts further salt growth. However, under conditions of limited supplemental solution, salt precipitation predominates, and salt can proliferate, further impacting injectivity. This paper proposes a variable injection strategy to mitigate the impact of salt precipitation on injectivity. It recommends transitioning from low to high flow injection rates as early as possible to prevent the reflow of the solution near the injection interface, thereby minimizing salt accumulation and its adverse effects on injectivity.

中文翻译：

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可变注入操作条件下盐析行为及其对注入能力影响的实验研究

在咸水层中二氧化碳地质封存期间，盐沉淀问题会降低储层注入能力并显着增加注入成本。注入过程中气体供应的变化可能导致二氧化碳注入速率的波动。注入参数的突然变化会影响储层压力的分布和盐水运移行为，从而影响盐析动力学。本研究采用设计的具有代表性地质边界条件的微观模型来研究可变注入条件下的盐析行为，实验条件为大气压和50℃。 CO 注入流速范围为 0.5 mL/min 至 4 mL/min。研究结果表明，在不同的注入条件下，注气速率的变化会引起储层溶液的波动，导致形成以入口附近盐簇生长为特征的“湿盐屏障”。这种现象显着削弱了单射性。当引入足够的补充溶液时，大部分先前沉淀的盐最初被溶解，最终达到限制盐进一步生长的动态平衡。然而，在补充溶液有限的条件下，盐沉淀占主导地位，并且盐会扩散，进一步影响注入能力。本文提出了一种可变注入策略来减轻盐析出对注入能力的影响。建议尽早从低流量注入速率过渡到高流量注入速率，以防止注入界面附近的溶液回流，从而最大限度地减少盐积累及其对注入能力的不利影响。