Dual-objective enhancement of CO2 injection and hydrate conversion for CO2 solid sequestration in submarine sediments via penicillin G sodium solution pre-injection

CO2 hydrate provides an important way for the long-term stable CO2 geological sequestration considering CO2 has potential self-sealing ability in submarine hydrate stable zone. However, the insufficient displacement efficiency of pore water and hydrate conversion rate pose significant challenges to ensuring long term CO2 injection and hydrate sequestration under shallow burial sediments. Here, to enhance CO2 injection into water-saturated sediments and hydrate conversion, we report a novel self-emulsification injection approach via penicillin G sodium solution pre-injection, which enables the rapid dispersion of injected CO2 into the pore water as micro- and nano-sized CO2 droplets in submarine sediments. The effects of liquid CO2 injection rate, flow distance, sediment particle size, and reagent dosage on droplet dispersion were quantitatively analyzed. On this basis, we further tested its complex behaviors of displacement flow and hydrate formation. The results indicate that compared to conventional liquid CO2 injection, self-emulsification injection effectively reduces injection pressure by 25 %–49 % and achieves the CO2 storage density up to 181 kg/m3, indicating that this method is more suitable for rapid and large-scale CO2 injection on the seabed. Moreover, the sufficiently small CO2 microdroplets generated by self-emulsification flow almost eliminate the interphase hydrate membrane effect, thereby increasing the CO2 hydration rate to over 70 %. This provides a guarantee for the effective establishment of CO2 hydrate sealing cap in shallow seabed sediments. Given its comprehensive excellent performance, the self-emulsification injection technology is expected to significantly advance the hydrated CO2 sequestration.