CO2 hydrate caps can effectively reduce the leakage risk from subsea CO2 sequestration. TBAB (tetrabutylammonium bromide) affects temperature and pressure required for the CO2 hydrate formation, which improves hydrate cap application. This study analyzes hydrate formation and decomposition characteristics in TBAB + CO2 system under different initial pressures and TBAB concentrations. The results show that the addition of TBAB effectively expand CO2 hydrate stable area and prevent CO2 leakage. 5 wt% TBAB not only provides crystal nucleus for hydrate formation and shortens the induction period, but also increases CO2 hydrate cap temperature to 290.3 K. The hydrate decomposition process in TBAB system is divided into CO2 ·nCO2 and TBAB·26H2O·nCO2 decomposition stage. Comparing with hydrate decomposition process in pure water system, it is found that TBAB mainly affects the second stage of hydrate decomposition process. In 5 wt% TBAB system, the hydrate decomposition process was affected by TBAB after more than 68 % hydrate decomposition. It is found that the hydrate decomposition rate with TBAB is almost 1/7 of that without TBAB. This study provides experimental support for expanding the application of CO2 hydrate caps, and provides a basis for determining the geological storage area of CO2 in sediments.

Formation and decomposition characteristics of CO2+TBAB hydrate for a safer CO2 storage