Li Yujiang, Li Chuanxian, Zhao Zhiqi, Cai Wei, Xia Xue, Yao Bo, Sun Guangyu, Yang Fei
College of Pipeline and Civil Engineering, China University of Petroleum, Qingdao, Shandong 266580, People's Republic of China.
ACS Omega. 2022 Feb 22;7(9):8023-8035. doi: 10.1021/acsomega.1c07174. eCollection 2022 Mar 8.
In oil fields, the formation of water-in-waxy crude oil emulsion is inevitable. The dissolved/crystallized state wax can interact with asphaltenes and then greatly affect the emulsion stability. However, studies on this aspect are still insufficient. In this work, the effects of the test temperature (30 °C well above the wax appearance temperature (WAT) and 15 °C well below the WAT) and asphaltene concentration (0∼1.5 wt %) on the stability of the water-in-model waxy crude oil emulsions containing 10 wt % wax were systematically investigated. When the model crude oils contain no wax, the flowability of the oils is good and the asphaltene concentration has little influence on the oil rheology. Increasing the asphaltene concentration facilitates the adsorption of asphaltenes to the oil-water interface, thus reducing the interfacial tension and water droplet size while enhancing the interfacial dilatational modulus. The stability of the emulsions improves with the increase in the asphaltene concentration, but the emulsions are still unstable. When the model crude oils contain 10 wt % wax, the WAT slightly decreases from the initial 25 to 24 °C after the addition of asphaltenes. The oil rheology is greatly improved by the addition of 0.05 wt % asphaltenes. With the further increase of the asphaltene concentration, the improved rheological ability of the asphaltenes deteriorates rapidly. At the asphaltene concentration of 1.5 wt %, the oil rheology is dramatically aggravated. The stability of the emulsion containing 10 wt % wax is mainly controlled by two aspects: on the one hand, the dissolved-state wax (30 °C) could facilitate the adsorption of asphaltenes to the interface, further reduce the interfacial tension and the water droplet size, and enhance the interfacial dilatational modulus; on the other hand, the wax crystals precipitated in the oil phase (15 °C) can form a stronger network structure at relatively high asphaltene concentrations (0.5∼1.5 wt %) and then immobilize the water droplets. The above two aspects greatly improve the sedimentation and coalescence stabilities of the emulsions at 15 °C. In addition, we did not find persuasive evidence showing that the wax could crystallize around the water droplets and strengthen the oil-water interfacial films.
在油田中，含蜡原油形成水包油乳液是不可避免的。溶解/结晶态的蜡会与沥青质相互作用，进而极大地影响乳液的稳定性。然而，这方面的研究仍不充分。在本工作中，系统研究了测试温度（高于析蜡温度（WAT）30℃以及低于WAT 15℃）和沥青质浓度（0∼1.5 wt%）对含10 wt%蜡的模拟含蜡原油乳液稳定性的影响。当模拟原油不含蜡时，油的流动性良好，沥青质浓度对油的流变学影响较小。增加沥青质浓度有助于沥青质吸附到油水界面，从而降低界面张力和水滴尺寸，同时提高界面扩张模量。乳液的稳定性随沥青质浓度的增加而提高，但乳液仍然不稳定。当模拟原油含10 wt%蜡时，加入沥青质后WAT从初始的25℃略微降至24℃。加入0.05 wt%沥青质可使油的流变学得到极大改善。随着沥青质浓度的进一步增加，沥青质改善流变学的能力迅速恶化。在沥青质浓度为1.5 wt%时，油的流变学急剧恶化。含10 wt%蜡的乳液稳定性主要受两方面控制：一方面，溶解态蜡（30℃）可促进沥青质吸附到界面，进一步降低界面张力和水滴尺寸，并提高界面扩张模量；另一方面，在油相中沉淀的蜡晶体（15℃）在相对较高的沥青质浓度（0.5∼1.5 wt%）下可形成更强的网络结构，进而使水滴固定。上述两方面极大地提高了乳液在15℃时的沉降稳定性和聚并稳定性。此外，我们未找到有说服力的证据表明蜡会在水滴周围结晶并强化油水界面膜。
