Spontaneous Deformation of Oil Clusters Induced by Dual Surfactants for Oil Recovery: Dynamic Study from Hele-Shaw Cell to Wettability-Altered Micromodel
Crude oil often contains long-chain fatty acid components. The fatty acid usually exists as a dissociative anionic surfactant in the oil phase. This study introduced a novel cationic surfactant to absorb the in situ anionic surfactant. Thus, a dual surfactant system was formed, and surfactant aggregates were produced near the water–oil interface. Due to the viscoelastic and fragile aggregates, spontaneous oil deformation and splitting were discovered as a novel mechanism for chemical enhanced oil recovery (EOR). First, we used a water phase doped with stearyltrimethylammonium chloride to displace the heavy oil with palmitic acid in the Hele-Shaw cell. The fingering patterns were observed in the water flooding (WF) and chemical flooding (CF) systems under different flow rates. After that, the experiments were transferred to the wettability-altered micromodel to simulate real oil recovery applications. The Hele-Shaw cell experiments show that viscous fingering was intensive at a low flow rate whereas it was significantly suppressed at a high flow rate in the CF system. The micromodel experiments show that oil recovery is higher in the CF system than in the WF system. The spontaneous cocurrent and counter-current oil blebbing was observed in the dynamic CF process. As the blebbing developed to a certain degree, the oil phase split into tiny droplets that could easily pass through the pore spaces. Additionally, the wettability was also altered from oil-wet to water-wet. As a result, oil recovery was improved significantly. The residual oil was classified into cluster, ganglia, and singlet based on the circularity and Euler number. We found the large clusters dominated in the WF system, whereas the small size of ganglia and singlets were the main forms in the CF system. The new chemical used can be applied for large-scale industrial EOR fields due to its good performance and low cost.
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