The interactions of crude oil with calcite surface are influenced by the Ca²⁺, Mg²⁺, and SO₄^2– ions in the aqueous solution in the context of wettability alteration and enhanced oil recovery; however, their effects are not well understood from the fundamental perspective. The force spectroscopy techniques that measure the attractive and repulsive forces between oil droplets and solid surfaces are crucial in developing this understanding. In this study, we investigated the effects of Ca²⁺, Mg²⁺, and SO₄^2– ions on calcite–oil interactions by immobilizing a droplet of crude oil to a tipless cantilever and used this “soft tip” to probe the calcite surface in different salt solutions with atomic force microscopy (AFM). The force behaviors at approach curves and the adhesion values at retract curves showed that the attractive calcite–oil interactions in the NaCl solution were enhanced by Mg²⁺ ions while the attractive interactions were mitigated by Ca²⁺ ions. In contrast, the calcite–oil interactions became repulsive in the presence of SO₄^2– ions with an observation of small adhesions in the Na₂SO₄ solution. The adhesion works were correlated to the “effective contact angles” to evaluate the effects of Ca²⁺, Mg²⁺, and SO₄^2– ions on calcite wettability. The results suggested that the Mg²⁺ ions made the calcite surface more oil-wet but the Ca²⁺ and SO₄^2– ions made the calcite surface more water-wet compared to indifferent ions.

中文翻译：

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通过“软尖端”原子力显微镜（AFM）探索Ca 2 ⁺，Mg ²⁺和SO ₄ ^2–对方解石-油相互作用的影响

在改变润湿性和提高采收率的情况下，水溶液中的Ca 2 ⁺，Mg ²⁺和SO ₄ ^2–离子影响原油与方解石表面的相互作用。但是，从基本的角度来看，它们的作用还不是很清楚。力谱技术可测量油滴与固体表面之间的吸引力和排斥力，对于发展这种理解至关重要。在这项研究中，我们研究了Ca 2 ⁺，Mg ²⁺和SO ₄ ^2–通过将一滴原油固定在无尖头的悬臂上，使方解石与油之间的相互作用产生离子，并通过原子力显微镜（AFM）使用该“软尖头”在不同盐溶液中探查方解石表面。接近曲线处的力行为和缩回曲线处的附着力值表明，Mg ²⁺离子增强了NaCl溶液中的方解石-油之间的吸引力，而Ca ²⁺离子则减少了吸引力。相反，在存在SO ₄ ^2–离子的情况下，方解石与油的相互作用变得排斥，并且观察到Na ₂ SO _4中的粘附力很小。解。粘附作用与“有效接触角”相关，以评估Ca 2 ⁺，Mg ²⁺和SO ₄ ^2–离子对方解石可湿性的影响。结果表明，与普通离子相比，Mg ²⁺离子使方解石表面更油润湿，而Ca ²⁺和SO ₄ ^2–离子使方解石表面更水润湿。