Biosurfactant as an Enhancer of Geologic Carbon Storage: Microbial Modification of Interfacial Tension and Contact Angle in Carbon dioxide/Water/Quartz Systems

摘要

Injecting and storing of carbon dioxide (CO_(2)) in deep geologic formations is considered as one of the promising approaches for geologic carbon storage. Microbial wettability alteration of injected CO_(2)is expected to occur naturally by microorganisms indigenous to the geologic formation or microorganisms intentionally introduced to increase CO_(2)storage capacity in the target reservoirs. The question as to the extent of microbial CO_(2)wettability alteration under reservoir conditions still warrants further investigation. This study investigated the effect of a lipopeptide biosurfactant—surfactin, on interfacial tension (IFT) reduction and contact angle alteration in CO_(2)/water/quartz systems under a laboratory setup simulating in situ reservoir conditions. The temporal shifts in the IFT and the contact angle among CO_(2), brine, and quartz were monitored for different CO_(2)phases (3 MPa, 30°C for gaseous CO_(2); 10 MPa, 28°C for liquid CO_(2); 10 MPa, 37°C for supercritical CO_(2)) upon cultivation of Bacillus subtilis strain ATCC6633 with induced surfactin secretion activity. Due to the secreted surfactin, the IFT between CO_(2)and brine decreased: from 49.5 to 30 mN/m, by ～39% for gaseous CO_(2); from 28.5 to 13 mN/m, by 54% for liquid CO_(2); and from 32.5 to 18.5 mN/m, by ～43% for supercritical CO_(2), respectively. The contact angle of a CO_(2)droplet on a quartz disk in brine increased: from 20.5° to 23.2°, by 1.16 times for gaseous CO_(2); from 18.4° to 61.8°, by 3.36 times for liquid CO_(2); and from 35.5° to 47.7°, by 1.34 times for supercritical CO_(2), respectively. With the microbially altered CO_(2)wettability, improvement in sweep efficiency of injected and displaced CO_(2)was evaluated using 2-D pore network model simulations; again the increment in sweep efficiency was the greatest in liquid CO_(2)phase due to the largest reduction in capillary factor. This result provides novel insights as to the role of naturally occurring biosurfactants in CO_(2)storage and suggests that biostimulation of biosurfactant production may be a feasible technique for enhancement of CO_(2)storage capacity.