Experimental study on natural gas hydrate exploitation: Optimization of methane recovery, carbon dioxide storage and deposit structure preservation

Aim of this work is locating how CO2 replacement into methane hydrate deposits may be performed, in order to increase both methane recovered and carbon dioxide stored quantities. The experimental section deals with the study of natural gas hydrate formation process and replacement of methane, contained into water cages, with carbon dioxide. In particular, the formation of methane hydrate is analyzed to understand the parameters that most influence the replacement process. A total of 10 tests were carried out in a laboratory scale reactor. Test 1–8 were performed adopting thermal stimulation as replacement technique, while in Test 9 and Test 10 depressurization was used. Results obtained have led to the conclusion that the rate of methane hydrate formation positively influences the percentage of CO2 stored, while the initial saturation of the sand pores has a negative effect. The presence of hydrate agglomerates hinders the gas transition preventing the replacement process. Finally, a greater quantity of CO2 hydrate, both via replacement process and via new hydrate formation, is related to a higher deposit structure preservation. As emerges from the experimental tests, the adopted replacement strategy influences the experimental relationships.