The presence of asphaltenes and polar compounds in a crude oil plays a major role in dictating the type of wettability it displays with oil reservoir rocks. The main objective of this study was to investigate the effect of the asphaltenes structure and other polar compounds in altering rock wettability. Five, natural crude oil samples were used with varying asphaltene (6.4 to 11.6), total nitrogen (0.029 to 0.097) and sulfur (2.259 to 4.234) contents, all in mass%. Crude oil characterization showed the asphaltene samples to consist of condensed hydrocarbon and sulfur aromatic molecules with one or two sulfur atoms per molecule. The weight-average numbers of fused aromatic rings for hydrocarbon molecules were 6 to 7 and for sulfur-containing molecules was an average of 8 aromatic rings, where the aromatic systems were substituted with short alkyl chains of less than 20 carbon atoms. Based on mass spectral evidence, the average empirical molecular structures of the asphaltenes were constructed and they were all found to be relatively similar. Entrained maltene species with 2 to 5 aromatic rings with longer alkyl chains were also found. Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) was used to characterize each crudes’ asphaltenes fractions. Three rock samples with mineral compositions of 100% dolomite (D100), 100% calcite (C100), and 63% calcite + 37% dolomite (C63D37) were used. Variation of the contact angle with time was measured using brine, as the external phase, and the five crudes on the rock samples. The interfacial tension (IFT) between brine and the five crudes were also measured. Among the five crude types, the three rocks show the strongest wetting tendency when contacted by type V oil. These were 129.2°, 109.2°, and 135.1° for D100, C100 and C63D37, respectively. Interestingly, wettability was not linearly correlated with asphaltene contents for all crude types. Wettability varied with the rock sample, nitrogen and sulfur contents, and crude’s non-asphaltenic composition. As a result, there is no strong evidence suggesting that the content nor the structure of the asphaltenes alone has a large effect on altering rock wettability.

中文翻译：

---

碳酸盐岩润湿性影响因素研究

原油中沥青质和极性化合物的存在在决定其与油藏岩石的润湿性类型方面起着重要作用。本研究的主要目的是研究沥青质结构和其他极性化合物对改变岩石润湿性的影响。使用五个天然原油样品，其沥青质（6.4至11.6）、总氮（0.029至0.097）和硫（2.259至4.234）含量各不相同，均以质量%计。原油表征显示沥青质样品由缩合烃和硫芳族分子组成，每个分子具有一个或两个硫原子。烃分子的稠合芳环的重均数量为6至7个，含硫分子的重均芳环数量为8个，其中芳族体系被小于20个碳原子的短烷基链取代。根据质谱证据，构建了沥青质的平均经验分子结构，并且发现它们都相对相似。还发现了带有 2 至 5 个芳环和较长烷基链的夹带马丁烯物质。使用傅里叶变换离子回旋共振质谱 (FT-ICR MS) 来表征每种原油的沥青质馏分。使用矿物成分为 100% 白云石 (D100)、100% 方解石 (C100) 和 63% 方解石 + 37% 白云石 (C63D37) 的三种岩石样品。使用盐水作为外相和岩石样品上的五种原油来测量接触角随时间的变化。还测量了盐水和五种原油之间的界面张力（IFT）。在五种原油类型中，三种岩石在与V类油接触时表现出最强的润湿倾向。D100、C100 和 C63D37 的角度分别为 129.2°、109.2° 和 135.1°。有趣的是，润湿性与所有原油类型的沥青质含量并不线性相关。润湿性随岩石样品、氮和硫含量以及原油的非沥青质成分而变化。因此，没有强有力的证据表明沥青质的含量或结构单独对改变岩石润湿性有很大影响。