Impacts of Smart Waters on Calcite–Crude Oil Interactions Quantified by “Soft Tip” Atomic Force Microscopy (AFM) and Surface Complexation Modeling (SCM)

The interactions of calcite surface
with crude oil are influenced by the ionic chemistry of the injection
water in “smart water” flooding; however, the molecular
evidence of their influences is missing in the current studies. To
address this issue, we measured the calcite–oil interactions
in four kinds of smart waters by driving a droplet of crude oil (“soft
tip”) toward and away from the calcite surface using atomic
force microscopy (AFM). The force behaviors showed that the calcite–oil
interactions were repulsive in smart waters containing low concentrations
of Ca2+ ions, such as seawater (SW) and seawater with one-fourth
of Ca2+ concentration (SWCa), which have produced extremely
weak adhesions and works of adhesion in these two brines. In contrast,
the force curves showed “jump-in” behavior in seawater
with four times increased SO42– concentration (SWSO) or Mg2+ concentration decreased to one-fourth (SWMg) compared to SW, which
has produced extremely large adhesions and works of adhesion. The
underlying reasons for calcite–oil interactions in response
to different smart waters were investigated by the method of surface
complexation modeling (SCM), which combined a charge-distribution
multisite ion complexation (CD-MUSIC) model and a basic Stern model
(BSM) to describe the complex electrochemical reactions of calcite,
smart water, and crude oil. The adhesion energies were calculated
based on the surface complexations, which showed good agreements with
the AFM force results. The SCM results suggested that the weak calcite–oil
interactions in SW and SWCa solutions can be attributed to the mitigation
of cation (Ca2+) bridging interactions owing to a deficiency
in surface Ca2+ ions. The strong calcite–oil interactions
in SWSO and SWMg solutions are caused by a dramatic increase of cation
(Ca2+) bridging interactions due to an excess of surface
Ca2+ ions. Overall, the attractions of calcite surface
with crude oil follow the order SWCa < SW ≪ SWMg < SWSO,
which infers that the oil molecules may be easily displaced from the
calcite surface with smart waters containing low concentrations of
Ca2+ and SO42– ions but high concentrations of Mg2+ ions.

碳酸钙表面与原油之间的相互作用受“智能水”注水过程中的注入水离子化学性质的影响；然而，目前的研究中缺乏对其影响作用分子层面的证据。为解决此问题，本研究通过原子力显微镜（AFM）技术，驱动原油滴（“软尖端”）向碳酸钙表面靠近和远离，测量了四种智能水中碳酸钙-油相互作用。力行为学分析表明，在含有低浓度钙离子（Ca2+）的智能水中，如海水（SW）和四分之一钙离子浓度的海水（SWCa），碳酸钙-油相互作用表现为排斥性，这两种盐水中产生了极其微弱的粘附力和粘附功。相比之下，与SW相比，当海水中硫酸根离子（SO42–）浓度增加四倍（SWSO）或镁离子（Mg2+）浓度降低至四分之一（SWMg）时，力曲线表现出“跳跃”行为，这两种盐水中产生了极其巨大的粘附力和粘附功。通过表面络合模型（SCM）方法，探究了碳酸钙-油相互作用在不同智能水中的内在原因，该方法结合了电荷分布多站点离子络合（CD-MUSIC）模型和基本斯特恩模型（BSM），以描述碳酸钙、智能水和原油的复杂电化学反应。基于表面络合计算得到的粘附能，与AFM力测量结果吻合良好。SCM结果表明，SW和SWCa溶液中碳酸钙-油弱相互作用可归因于表面钙离子缺乏导致阳离子（Ca2+）桥接相互作用减弱。SWSO和SWMg溶液中碳酸钙-油强相互作用则是由表面钙离子过剩导致的阳离子（Ca2+）桥接相互作用显著增加所致。总体而言，碳酸钙表面与原油的吸引力顺序为SWCa < SW ≪ SWMg < SWSO，这表明在含有低浓度Ca2+和SO42–离子但高浓度Mg2+离子的智能水中，油分子可能更容易从碳酸钙表面被移除。