An approach to the high efficient exploitation of nature gas hydrate and carbon sequestration via injecting CO2/H2 gas mixture with varying composition

The combined technology integrating CO2/H2 injection and CH4 production with in situ steam reformation of CH4 has provided a promising way to address green energy production and CO2 storage. However, how to break through the mutual constraints between CH4 recovery and CO2 storage remains a big challenge. Here, we explored changing the composition of the injected gas at different stages to simultaneously achieve high CO2 sequestration and high CH4 recovery. The experimental results exhibit the high-level CH4 recovery ratios of 83-89 %. Meanwhile, this variable composition gas injection mode presented good performance in CH4 con-centration of produced gas and gas injection-production ratio, and showed outstanding H2 utilization efficiency. All these mean that the variable composition gas injection has better economics than other gas injection modes. Further calculation results of hydrate saturation and solid shrinkage volume suggest that adopting fixed CO2- containing (55 %) gas can realize non-destructive hydrate mining with a final CH4 recovery of 58 %; while the varying gas composition is to first enhance gas recovery and then repair the sediments with a basic repair ratio of > 70 %. Thus, we were able to keep hydrate saturation in the reservoir within safe thresholds and repair the reservoir before the possible occurrence of wellbore and formation damages by changing the gas composition of the injected gas. Therefore, this approach is greatly promising for high-efficient and safe exploitation of gas hydrate.