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

CO2 2 hydrate caps can effectively reduce the leakage risk from subsea CO2 2 sequestration. TBAB (tetrabutylammonium bromide) affects temperature and pressure required for the CO2 2 hydrate formation, which improves hydrate cap application. This study analyzes hydrate formation and decomposition characteristics in TBAB + CO2 2 system under different initial pressures and TBAB concentrations. The results show that the addition of TBAB effectively expand CO2 2 hydrate stable area and prevent CO2 2 leakage. 5 wt% TBAB not only provides crystal nucleus for hydrate formation and shortens the induction period, but also increases CO2 2 hydrate cap temperature to 290.3 K. The hydrate decomposition process in TBAB system is divided into CO2 2 center dot nCO2 2 and TBAB center dot 26H2O center dot nCO2 2 O center dot nCO 2 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 2 hydrate caps, and provides a basis for determining the geological storage area of CO2 2 in sediments.