Qu Haolin, Khishvand Mahdi, Piri Mohammad
Department of Petroleum Engineering, University of Wyoming, Laramie, Wyoming 82071-2000, United States.
Langmuir. 2023 Mar 21;39(11):3837-3852. doi: 10.1021/acs.langmuir.2c01765. Epub 2023 Mar 12.
This study uses in situ experimental investigation techniques to probe the synergistic effects of aqueous phase viscoelasticity and reduced interfacial tension on nonwetting phase displacement efficiency in natural porous media. Specifically, it examines the efficacy of viscoelastic surfactant (VES) solutions in enhancing oil recovery and investigates the pore-scale displacement mechanisms and VES-oil interactions. To this end, we first performed an extensive rheological characterization to select two VES solutions from multiple CTAB/NaNO (CTN) and Cocobetaine/SDS/NaCl (CSN) mixtures. The selected aqueous solutions were then used in unsteady-state imbibition experiments conducted on miniature, water-wet Prairie Shell carbonate core samples. The experiments were performed utilizing a high-pressure, high-temperature two-phase core-flooding apparatus integrated with a high-resolution X-ray imaging system to acquire pore-scale fluid occupancy maps during the displacements. The results indicate that the injection of the selected CSN and CTN solutions into the carbonate samples under capillary-dominated flow regimes boosts the oil recovery by 12 and 2%, respectively, compared to those of the base waterflood. The VES solutions lowered the oil-water interfacial tension and exerted significant shear forces at the entrance of pores. The shear forces could exceed the threshold surface free energy required to deform oil globules, and consequently, large oil clusters were fragmented into smaller blobs and eventually produced from the pore space. The higher oil recovery by CSN flooding was attributed to its stronger viscoelastic properties. The VES injection under the viscous-dominated flow regime intensified the frequency of oil globule fragmentation. As a result, residual oil saturation values were sharply reduced in the rock samples from 44 to 55% during the capillary-dominated flows to approximately 8%. The above-mentioned observations were also verified using morphological analysis of residual oil clusters. The impacts of VES flooding on the pore-scale oil configuration and the fragmentation of large oil clusters were particularly evident at higher VES flow rates.
本研究采用原位实验研究技术，探究水相粘弹性和降低的界面张力对天然多孔介质中非润湿相驱替效率的协同作用。具体而言，研究了粘弹性表面活性剂（VES）溶液在提高原油采收率方面的效果，并研究了孔隙尺度的驱替机制以及VES与油之间的相互作用。为此，我们首先进行了广泛的流变学表征，从多种十六烷基三甲基溴化铵/硝酸钠（CTN）和椰油酰胺甜菜碱/十二烷基硫酸钠/氯化钠（CSN）混合物中选择了两种VES溶液。然后，将所选的水溶液用于在小型水湿草原贝壳碳酸盐岩心样品上进行的非稳态渗吸实验。实验使用高压、高温两相岩心驱替装置与高分辨率X射线成像系统相结合进行，以获取驱替过程中的孔隙尺度流体占有率图。结果表明，在毛细管主导的流动状态下，将所选的CSN和CTN溶液注入碳酸盐岩样品中，与基础水驱相比，原油采收率分别提高了12%和2%。VES溶液降低了油水界面张力，并在孔隙入口处施加了显著的剪切力。这些剪切力可能超过使油滴变形所需的表面自由能阈值，因此，大的油团被破碎成较小的油滴，最终从孔隙空间中产出。CSN驱替采收率较高归因于其较强的粘弹性。在粘性主导的流动状态下注入VES增加了油滴破碎的频率。结果，在毛细管主导的流动过程中，岩石样品中的残余油饱和度值从44%至55%急剧降低至约为8%。上述观察结果也通过对残余油团的形态分析得到了验证。在较高的VES流速下，VES驱替对孔隙尺度油的形态和大油团破碎的影响尤为明显。
