Summary In mixed- to oil-wet reservoirs characterized by intense natural fracturing where the dominant displacement mechanism is gravity drainage, surfactant injection can lead to a shift in wettability and incremental oil production. In some cases, oil can also reimbibe back into the rock matrix after the oil saturation has been reduced upon initial exposure to surfactant, suggesting limited permanence in the wettability shift. The reimbibition phenomenon is investigated in this paper using Amott cells. Three cationic surfactants (C12-, C12–16-, C16-based) with interfacial tensions (IFT) between 0.18 and 0.95 mN/m were preselected to be evaluated. Current application of the C12-based surfactant in the Yates field is considered successful based on incremental oil recovery seen during the treatment. Silurian dolomite (SD) rock samples were flooded with Yates crude oil before being aged at 60°C for 6 weeks. For the imbibition tests, the aqueous surfactant solution was set as the external phase within the Amott cell, and the recovery of oil was recorded periodically. After the imbibition tests ended, the rock samples were placed in an inverse Amott cell with the Yates oil as the external phase. Baseline tests were first conducted to show that without a surfactant in the oil or brine, no imbibition occurred. With a surfactant concentration of 3,000 ppm, oil recovery at the end of the imbibition tests varied from 34 to 60% of the original oil volume in the core sample. During the reimbibition test, a large amount of oil was able to reimbibe into the rock, displacing the brine. Most of the displacement occurred within the first 2 weeks. The net oil recovery, taken as the final volume of oil recovered in the imbibition test minus the final volume of oil reimbibed into the rock, ranged from 0 to 18%. Given the possibility of surfactant dilution in field applications, another set of tests was conducted with 1,500 ppm. A reduction in oil recovery during imbibition was observed for all the tested surfactants. Partition coefficients were determined for each of the tested surfactants, and the ion-pair mechanism was used to explain the net oil recovery results. Lastly, the impact of rock permeability on reimbibition was investigated. Results show increasing permeability may lead to a linear response in oil reimbibition; therefore, minimizing the permeability range when selecting rock samples may be necessary when conducting the reimbibition test. The importance of oil reimbibition is demonstrated in the experimental study, and we make an argument for conducting both the imbibition and reimbibition tests to better evaluate surfactant efficacy. The improved understanding of wettability alteration should lead to advancements in chemical enhanced oil recovery (EOR) designs for field treatments.

中文翻译：

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耶茨油田原油复吸过程及其对采收率影响的调查

总结 在以强烈天然压裂为特征的混合至亲油油藏中，主要驱替机制是重力排水，注入表面活性剂可导致润湿性的转变和增加的石油产量。在某些情况下，油还可以在初次接触表面活性剂后油饱和度降低后重新吸收回岩石基质，这表明润湿性转变的持久性有限。本文使用 Amott 细胞研究了再吸收现象。三种阳离子表面活性剂（C12-、C12-16-、C16-基）的界面张力（IFT）在 0.18 和 0.95 mN/m 之间被预先选择进行评估。目前在 Yates 油田中 C12 基表面活性剂的应用被认为是成功的，基于在处理过程中看到的增量采油。志留系白云石 (SD) 岩石样品在 60°C 老化 6 周之前用 Yates 原油淹没。对于自吸试验，将表面活性剂水溶液设置为 Amott 池内的外相，并定期记录油的回收率。在自吸试验结束后，将岩石样品置于以耶茨油为外相的反阿莫特槽中。首先进行基线测试以表明在油或盐水中没有表面活性剂时，不会发生自吸。在表面活性剂浓度为 3,000 ppm 的情况下，自吸试验结束时的采油率在岩心样品中原始油体积的 34% 到 60% 之间变化。在复吸测试期间，大量油能够复吸到岩石中，置换了盐水。大部分移位发生在前两周内。净石油采收率，即在自吸试验中采收的最终石油体积减去再吸进岩石中的最终石油体积，范围为 0 至 18%。鉴于在现场应用中可能会稀释表面活性剂，我们使用 1,500 ppm 进行了另一组测试。对于所有测试的表面活性剂，观察到在自吸过程中采油率降低。确定了每种测试表面活性剂的分配系数，并使用离子对机制来解释净采油结果。最后，研究了岩石渗透率对再渗吸的影响。结果表明，增加渗透率可能会导致油再膨胀的线性响应；所以，在进行再膨胀测试时，可能需要在选择岩石样品时最小化渗透率范围。在实验研究中证明了油再吸收的重要性，我们提出了同时进行吸收和再吸收测试以更好地评估表面活性剂功效的论据。对润湿性改变的更好理解应该会导致用于现场处理的化学强化采油 (EOR) 设计的进步。