Experimental study on the CH4/CO2 replacement in the sand-clay systems with a high water content

Abstract

The CH4/CO2 replacement has been viewed as a promising method for mining natural gas hydrates (NGHs), which combines CH4 extraction with CO2 geological storage. In this study, the CH4/CO2 replacement in the sand-clay systems with a high water-cut was investigated where the effects of temperature, pressure, water content, additives, clay type and content on the CH4 replacement percentage (ηCH4), CO2 storage efficiency (ηCO2), replacement ratio (ηCH4/CO2) and consumption of free water were systematically studied. The results showed that the replacement temperature and pressure played an important role in CH4 extraction and CO2 storage. The CH4 replacement percentage increased as water content increased, and the highest value reached 62.65% at the water content of 84.75 wt%. The presence of NaCl and sodium dodecyl sulfate (SDS) improved the replacement efficiency compared to the pure water system. It was found that kaolinite clay had little effect on the CH4 replacement percentage and CO2 storage efficiency, while the free water consumption increased as its content increased. Montmorillonite showed a promoting effect on CH4 extraction but presented an inhibitory effect on CO2 storage, and the highest replacement ratio achieved 0.6060 at its mass fraction of 33.3 wt%. This study could provide important insights into the CH4 extraction and CO2 storage by CH4/CO2 replacement.