Changes in Heat and Energy During Depressurization-Induced Natural Gas Hydrate Dissociation in Porous Media

Natural gas hydrates (shortened as hydrates) are expected to be a prospective alternative to traditional fossil energies. The main strategy of exploring hydrates is achieved by dissociating solid hydrates into gas and water with the depressurization method. However, we have little knowledge on the changes in heat and energy, which are implicit essences compared with explicit temperature. Thus, this study for the first time investigates the evolutionary patterns of heat and energy during hydrate dissociation, by fully coupled thermal–hydraulic–mechanical–chemical modelling. A novel numerical technique (physics-based constrained conditions) is proposed to guarantee the stability and precision of the numerical computation. The classic Masuda’s experiment is used as a case study. Results show that the cumulative conduction heat tends to increase first and then decrease during the dissociation of hydrate, while the cumulative advection heat has the tendency to increase monotonically. External heat sources increase the energy, while phase change has a reduction effect on the change in energy. The role of conduction heat is minor, but the contribution of advection heat is considerable for the change in energy. Additionally, two implications are given for lab-scale experiments and in situ engineering from the perspective of energy. Our findings provide new insights into the mechanism of hydrate dissociation and are beneficial to the real-world engineering of hydrate exploration in terms of cost evaluation.