An equivalent state method for submarine spread modeling subject to hydrate dissociation

Spreading is one of the key factors shaping the ridge-and-trough submarine morphology. There is a certain spatial correlation between submarine spreading and the occurrence of methane hydrate, yet the mechanism is not well understood and numerical evidence of this process is insufficient. This study presents a numerical study on hydrate-induced submarine spreading. A novel scheme is developed to couple the thermal dissociation analysis of hydrate and large deformation analysis of spreading, in which an equivalent state method based on the theory of unsaturated soil strength is proposed to guarantee the physical continuity in phase pressures and phase saturations. A two-layer continental slope example in the South China Sea is used to investigate the key features of hydrate-induced submarine spreading. Three typical stages are identified: the initiation of spreading after hydrate dissociation, the propagation of basal shear band towards the downslope, and the formation of ridges and troughs. The simulated results are comparable to the field observations of submarine morphology in the presence of shallow hydrate reservoirs. The onset of spreading is primarily dominated by the length and continuity of hydrate layer, followed by its depth. This study reveals a potential mechanism on how the dissociated hydrate induces submarine spreading, which is beneficial for risk assessment of deep-sea infrastructures.