Insights into multistep depressurization of CH4/CO2 mixed hydrates in unconsolidated sediments

Natural gas hydrates (NGH) are potential energy resource and distributed in unconsolidated marine sediments. CH4–CO2 swapping combined with depressurization is a promising method for simultaneously enhancing CH4 recovery CO2 storage NGH. This was previously studied on CH4/CO2 mixed consolidated sediments but no such studies available In this study, we investigated dissociation characteristics of using slow multistep depressurization. were formed sandpack. The effects molar ratio (CH4-rich CO2-rich) hydrate, residual water saturation (9.2% to 31.7%) reservoir temperature (−3.3 °C 2.2 °C) production efficiencies mainly investigated, the results compared those bulk literatures. showed that preferably encaged hydrate than phenomenon most apparent CH4-rich recommended be exploited by Higher unbeneficial recovery, while lower value not conducive hydrate. Temperature below or above freezing point decided ice formation affected yield retention mass transfer. primarily dependent degree higher percent at depletion pressure. maximum increment concertation (6.5 mol%) highest efficiency (88.2%) achieved optimum 17.7% 0 °C. addition, key factor controlling performances, provided larger contact area among gas, mobile water. work could useful future NGH exploitation after injection into