Theoretical analysis of effective thermal conductivity for clayey hydrate-bearing sediments during hydrate dissociation and reformation processes

In general, apart from hydrate dissociation, the hydrate reformation phenomenon may occur during the natural gas hydrate (NGH) exploitations, which increases the risk of blockage accidents and should be further understood and controlled. Since the effective thermal conductivity (ETC) of the hydrate-bearing sediment (HBS) is a critical parameter controlling the heat transfer process and significantly affecting hydrate dissociation and reformation processes, it should be precisely predicted for enhancing the safe, efficient, and stable NGH exploitations. Thus, in this work, a novel analytical ETC model of HBS is proposed not only to quantitatively characterize various mechanisms during hydrate dissociation and reformation processes, but also to accurately determine ETC under effective stress conditions. The ETC predictions of the proposed model are validated against available experimental ETC data under various conditions, enhancing the reasonability of this model. And effects of several crucial parameters on ETC are deeply investigated. Results show that, with the increasing effective stress (axial stress and radial stress), ETC of HBS increases. And ETC increases in the early stage of hydrate dissociation, however, as the hydrate dissociation continues, the ETC of HBS decreases. Additionally, during hydrate reformation process, ETC of HBS shows a negative relation with the hydrate saturation under excess water condition and shows a positive relation under excess gas condition. Notably, the proposed model can offer insights into heat transfer characteristics under various NGH exploitation conditions, helping optimize the extraction plans.