Collini Harry, Jackson Matthew D
Novel Reservoir Modelling and Simulation Group, Department of Earth Science and Engineering, Imperial College London, UK; Now at BP International Centre for Business and Technology, Sunbury-on-Thames, Middlesex, UK.
Novel Reservoir Modelling and Simulation Group, Department of Earth Science and Engineering, Imperial College London, UK.
Adv Colloid Interface Sci. 2023 Oct;320:102962. doi: 10.1016/j.cis.2023.102962. Epub 2023 Jul 18.
Despite the broad range of interest and applications, controls on the surface charge of crude oil in aqueous solution remain poorly understood. The primary data source to understand the surface charge on crude oil comprises measurements of zeta potential on individual drops or emulsions obtained using the electrophoretic method (EPM). Here we (i) collate and review previous measurements of zeta potential on crude oil, (ii) compare and contrast the results, and (iii) report new measurements of zeta potential on crude oil wetting films and layers relevant to oil-saturated porous media, obtained using the streaming potential method (SPM). Results show that the zeta potential depends on electrolyte pH and the concentration of divalent ions Ca and Mg. Lower pH and higher concentration of these divalent ions yields more positive zeta potential. The isoelectric point (IEP) in simple NaCl electrolytes lies in the pH range 3-5. The IEP in simple CaCl and MgCl electrolytes can be expressed as pCa or pMg, respectively, and lies in the range 0-1. Close to the IEP, the zeta potential varies linearly with pH, pCa or pMg, suggesting simple Nernstian behaviour of the crude oil surface. The sensitivity of the zeta potential to pH, pCa and pMg decreases with increasing total ionic strength. The impact of pH, pCa and pMg on zeta potential varies significantly across different crude oils and differs from non-polar hydrocarbons. The potential for other multivalent ions to modify crude oil zeta potential has not been tested. Data for crude oil wetting films and layers, obtained using the SPM and strongly oil-wet porous substrates in which the solid surfaces are coated with the crude oil of interest, are comparable to those obtained using emulsions and the EPM, suggesting that the controls on zeta potential on crude oil are the same irrespective of whether the oil forms droplets or wetting layers. The literature data reviewed here, along with new measured data, provide important insight into the effect of pH, and the concentration of divalent ions, on the zeta potential of crude oil in aqueous solution. They demonstrate relationships between ion concentration and zeta potential that are observed irrespective of crude oil composition. They also show that the crude oil composition plays a role, yet no consistent trends are observed between zeta potential and commonly measured bulk oil properties, possibly because bulk properties do not reflect the concentrations of interfacially active species in crude oil that may impact the development of surface charge. Moreover, data are extremely scarce for complex, high ionic strength electrolytes or at elevated temperature. The data reviewed and reported here have broad relevance to many engineering and industrial activities involving crude oil.
尽管原油在水溶液中的表面电荷具有广泛的研究兴趣和应用，但人们对其表面电荷的控制仍知之甚少。了解原油表面电荷的主要数据来源包括使用电泳法（EPM）对单个液滴或乳液的zeta电位进行测量。在此，我们（i）整理并回顾先前对原油zeta电位的测量结果，（ii）比较和对比这些结果，（iii）报告使用流动电位法（SPM）对与油饱和多孔介质相关的原油润湿膜和层的zeta电位进行的新测量结果。结果表明，zeta电位取决于电解质pH值以及二价离子Ca和Mg的浓度。较低的pH值和较高浓度的这些二价离子会产生更正的zeta电位。在简单的NaCl电解质中，等电点（IEP）位于pH值3 - 5的范围内。在简单的CaCl和MgCl电解质中，IEP可分别表示为pCa或pMg，且位于0 - 1的范围内。接近IEP时，zeta电位随pH值、pCa或pMg呈线性变化，表明原油表面具有简单的能斯特行为。zeta电位对pH值、pCa和pMg 的敏感性随总离子强度的增加而降低。pH值、pCa和pMg对zeta电位的影响在不同原油之间存在显著差异，并且与非极性烃类不同。其他多价离子对原油zeta电位的影响尚未得到测试。使用SPM并结合强亲油多孔基质（其中固体表面涂有所关注的原油）获得的原油润湿膜和层的数据，与使用乳液和EPM获得的数据具有可比性，这表明无论油形成液滴还是润湿层，对原油zeta电位的控制都是相同的。这里回顾的文献数据以及新的测量数据，为pH值和二价离子浓度对水溶液中原油zeta电位的影响提供了重要见解。它们展示了离子浓度与zeta电位之间的关系，这种关系与原油组成无关。它们还表明原油组成起到了一定作用，但在zeta电位与通常测量的原油整体性质之间未观察到一致的趋势，这可能是因为整体性质不能反映原油中可能影响表面电荷形成的界面活性物质的浓度。此外，对于复杂的高离子强度电解质或在高温下的数据极其稀少。这里回顾和报告的数据与许多涉及原油的工程和工业活动具有广泛的相关性。
