Wettability alteration of carbonate rocks at reservoir conditions by novel poly(ethylene oxide) gemini surfactants

1. Some of the locally synthesized cationic gemini surfactants have strong WA performance on oil-wet limestone cores; 2. Spacer structure and unsaturation have significant impact on gemini surfactants’ WA performance; When the spacers have similar structures, higher unsaturation led to higher negative effect on WA performance; 3. Difference counter-ion types also led to different WA performance; 4. There exists a critical concentration. As the concentration increased, the extent of WA increased and then stabilized or reduced at that critical concentration (around 0.05 wt% for GS3). 5. Temperature increase from 20°C to 80°C didn’t cause significant difference in WA performance of GS8. This result ensures the efficacy of GS8 under reservoir temperature. 6. CaCl2 and MgCl2 have negative effect on the WA performance of gemini surfactant GS3; SO4 has positive effect on the WA performance; Increased salinity impaired the WA performance.