Convection-conduction heat transfer and seepage in hydrate-bearing sandy sediments under hot fluid injection: A thermo-hydro-chemical perspective

In this study, a gas-saturated hydrate sample was synthesized within sand sediment, and thermal stimulation via a central injection well induced hydrate dissociation. Heat transfer and seepage characteristics of hydrate-bearing sandy sediments were examined during fluid injection. A heat transfer model was established to analyze convective heat transfer and hydrate saturation distribution at various regions of the sediment. The results indicate that the seepage of injected fluid in the sediment was non-uniform, with slower vertical flow, leading to the formation of a liquid layer at the top. Thermal stimulation led to rapid near-wellbore temperature rises from strong convective heat transfer during the early injection stages, with the exception of hot brine injection. The temperature distribution at the top edge of the sediment remained largely uniform, while heat conduction led to a limited temperature rise at the bottom edge. Convective heat transfer intensity increased with higher injection temperatures near the wellbore, with seawater injection outperforming pure water injection, and the heat transfer mechanisms near the wellbore alternating between convection and conduction. Hydrate dissociation advanced radially, peaking in the middle sediment region; warm seawater and higher injection temperatures notably enhanced dissociation, especially near the wellbore and edges.