Experimental and Numerical Study of Methane Hydrate Growth in Sand Sediments: Effect of Geometry and Water Saturation

Abstract

Natural gas hydrates represent a vast energy resource, yet their formation in fine-grained sediments remains poorly constrained. Here, CH4 hydrate growth in a quartz sand column with distinct geometries, solid versus hollow, was measured at an initial pressure of 6 MPa and temperatures ranging from 274.15 to 278.15 K. The results showed that the CH4 consumption rates in the hollow sand column were significantly higher than those in the solid column and reached equilibrium within approximately 30 min. A terminal ratio of water saturation to hydrate saturation Sw/Sh was found to be around 0.6 for initial water saturations above 40%, indicating that a fixed fraction of pore water was kinetically inaccessible as hydrate shells encapsulated water films. In addition, an increase in temperature did not reduce the total amount of hydrate formation but prolonged the formation process. On the basis of these facts, a numerical model incorporating macro-scale front propagation and micro-scale water film encapsulation was developed, which reproduced experimental observations with deviations below 7.4%. Simulations demonstrated that dual-front advancement in the hollow geometry promoted uniform hydrate distribution, whereas thermal resistance in the solid pillar induced a localized temperature rise and reduced hydrate conversion. Geometry-dependent heat transfer, capillary-driven fluid redistribution, and progressive loss of reactive interfacial areas were collectively suggested to govern hydrate growth, providing a predictive framework for resource assessment and production strategies in heterogeneous sedimentary environments.