Pilot-Scale Experimental Investigation of Multifield Coupling and Heterogeneity during Hydrate Dissociation

Natural gas hydrates are considered as a potential energy resource for the future. In this study, for the first time, the pilot-scale hydrate simulator (PHS), with an effective volume of 117.8 L, was applied to investigate the multifield coupling (decomposition-heat transfer-flow) and heterogeneity during hydrate dissociation using the newly added flow-field measurement system. The experimental method adopted in this study is the huff and puff in conjunction with depressurization (H&P-D). The experimental results show that the middle layer of the hydrate reservoir is the area where the hydrates are most likely to reform in the depressurization stage. Moreover, this layer has the highest pressure during the huff and puff production stage, which makes the production well in the middle layer contribute little to the natural gas production. Through the coupling of decomposition-heat transfer-flow, it was found that the hydrates far from the center of the lower layer of the hydrate reservoir are decomposed until the ninth cycle of huff and puff (H&P). It was determined from the analysis of the pressure field and heat transfer field that the distribution of the hydrates is not uniform and the decomposition is heterogeneous. The hydrates are most abundant in the lower layer and least abundant in the upper layer. The time for hydrate decomposition is longest in the lower layer and shortest in the upper layer. This experiment makes up for the lack of flow-field analysis of the hydrate decomposition process in previous studies, and these experimental findings provide theoretical support for the future exploitation of natural gas hydrates.

Automated summary

In this study, a pilot-scale hydrate simulator with an effective volume of 117.8 L was used for the first time to investigate multifield coupling and heterogeneity during hydrate dissociation. The results show that hydrate decomposition is heterogeneous, with the most abundant hydrates in the middle of the lower layer and the longest decomposition time in the lower layer.