Specificity and Synergy at the Oil–Brine Interface: New Insights from Experiments and Molecular Dynamics Simulations,Energy & Fuels

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Specificity and Synergy at the Oil–Brine Interface: New Insights from Experiments and Molecular Dynamics Simulations
Energy & Fuels ( IF 5.2 ) Pub Date : 2021-08-30 , DOI: 10.1021/acs.energyfuels.1c02133
Safwat Abdel-Azeim ₁ , Sivabalan Sakthivel ₁ , Tarek A. Kandiel ₂ , Mazen Y. Kanj ₁

Affiliation

The interfacial tension (IFT) between oil and brine is a key parameter affecting the enhanced oil recovery process. Despite the several theoretical and experimental investigations on the oil–brine system, the salinity effect on the IFT of oil–brine is still not fully understood. There is a contradiction in the literature rather than consistency. In the present study, we combine molecular dynamics (MD) simulations with the pendant drop method to investigate the molecular interactions at the oil–brine interface to better understand the salinity–IFT relationship. Herein, we are taking into account the complex composition of both crude oil and brine and the pH and total acid number. Different salinity conditions have been considered ranging from deionized water to connate (formation) water. We also consider the effects of individual brines of the main alkali salts (i.e., NaCl, MgCl₂, and CaCl₂) that are common in carbonate reservoirs. The specificity and synergy of the molecular interactions are observed via the confrontation of the results of the mixed brines (seawater and formation water) with those of the individual brines. We observed a significant impact of the divalent cations on the oil–brine interfacial tension. Due to the specificity of the organic acid–Ca²⁺ type of interaction and the synergy between the different ions, complete encapsulation of the Ca²⁺ ions has been observed within the formation water brine. This induces the depletion of the organic acids at the interface and thus increases the IFT. Such ionic encapsulation has not been observed in the individual brines because the cation–anion (Cl^–) and the cation–water interactions are strong enough to prevent the cation–acid encapsulation. The interplay between the electrostatic interactions and the cations’ dehydration-free energies is the main parameter that controls their specificity and synergy, affecting the oil–brine interfacial properties. This work provides important details on the ionic interactions influencing the interfacial properties between crude hydrocarbons and brine.

中文翻译：

油-盐水界面的特异性和协同作用：来自实验和分子动力学模拟的新见解

油和盐水之间的界面张力 (IFT) 是影响提高采收率过程的关键参数。尽管对油-卤水系统进行了一些理论和实验研究，但盐度对油-卤水 IFT 的影响仍未完全了解。文献中存在矛盾而不是一致性。在本研究中，我们将分子动力学 (MD) 模拟与悬滴法相结合，研究油-盐水界面的分子相互作用，以更好地了解盐度-IFT 关系。在此，我们考虑了原油和盐水的复杂成分以及 pH 值和总酸值。考虑了从去离子水到原生水（地层水）的不同盐度条件。₂和 CaCl ₂ )，这在碳酸盐岩储层中很常见。通过将混合卤水（海水和地层水）的结果与单个卤水的结果进行对比，可以观察到分子相互作用的特异性和协同作用。我们观察到二价阳离子对油-盐水界面张力的显着影响。由于有机酸-Ca ²⁺类型相互作用的特异性以及不同离子之间的协同作用，在地层水卤水中观察到Ca ²⁺离子的完全包封。这会导致界面处有机酸的消耗，从而增加 IFT。在单独的盐水中没有观察到这种离子包封，因为阳离子 - 阴离子（Cl^– ) 并且阳离子-水相互作用足够强以防止阳离子-酸包封。静电相互作用和阳离子的无脱水能之间的相互作用是控制它们的特异性和协同作用的主要参数，影响油-盐水界面性质。这项工作提供了关于影响粗烃和盐水之间界面性质的离子相互作用的重要细节。

更新日期：2021-09-16

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