Construction and performance evaluation of novel compound oil displacement system for enhanced oil recovery

Conventional methods of flooding leave behind a significant amount of oil films that adhere to the rock surfaces. Developing novel compound oil displacement system to achieve efficient oil film peeling and migration is of great significance for further enhanced oil recovery. Herein, a novel compound oil displacement system was developed through optimization experiments using a binary surfactant mixture composed of SDBS and BS-18, along with a wetting regulator known as CAS. The minimum interfacial tension attained of compound oil displacement system was 0.0042 mN/m, indicating an ultra-low level. Meanwhile, the compound system could alter the rock surface wettability from oleophilic to strong hydrophilic, with the underwater oil contact angle substantially increasing from 18 degrees to 123.1 degrees. The compound system demonstrated remarkable stability at high water salinity (60000 ppm) and high temperature (90 degrees C). The surface strong hydrophilicity contributed to the excellent oil film peeling performance of compound system, leading to an 89.14% reduction in the oil film area within 12 h. The superior ability in interfacial tension reduction and wettability alteration of the compound system facilitated the "peeling off" and "migrating out" process of the residual oil film, and impressive enhanced oil recovery of 18.68% was achieved compared to that of the surfactant mixture SDBS/BS-18 (7.23%) and wetting regulator CAS (7.64%). It is believed that the outcomes of this work provide valuable insights into the design and optimization of effective oil displacement systems for residual oil development.