Evolution Law of Gas Hydrate Microstructure and Morphological Characteristics during Gas Hydrate Formation and Dissociation Process in Sand Sediments Combined with Micro-CT Observation

Abstract

The morphological and microstructural characteristics of gas hydrates within pores exert significant influence on the petrophysical properties of gas hydrate-bearing sediments; however, the evolution of these properties throughout hydrate formation and dissociation remains ambiguous. The dynamic pore-scale process of gas hydrate formation and dissociation in incompletely water-saturated sediments was visualized by X-ray micro-computed tomography (X-ray micro-CT). The shape factor, volume, surface area, Euler characteristics, and fractal dimensions of individual gas hydrate clusters were chosen to describe the evolution of microstructure and morphology during the formation and dissociation of the hydrates within the sediments. The results show that the topological parameters of individual hydrate clusters change obviously during the process of hydrate formation and dissociation. It is speculated that the isolated gas hydrate clusters in the pores decompose earlier in the initial stage of the experiment, and when the gas hydrate saturation is lower than the critical threshold, the dissociation of the interpore gas hydrate framework connected by the pore throat is dominant.