# Formation Kinetics and Morphology Characteristics of Natural Gas Hydrates in Sandstone Fractures
## 4 Conclusions  
This study conducted in situ experiments on the formation, dissociation, and secondary formation of CH\({}_{4}\) hydrates in sandstone fractures. It analyzed the effects of fracture width, shape, roughness, and other factors on the hydrate induction time, total formation duration, gas consumption, as well as on kinetic and morphological characteristics of hydrate formation, and explored the influence of factors related to dissociation and hydrate reformation. The specific conclusions are as follows:  
1. In Type I fractures, under 3 mm fracture width conditions, the hydrate induction time is longer than those under the other two fracture width conditions, with a larger gas consumption of \(3.82\times 10^{-1}\) mol. However, the differences in gas consumption among the three types of fractures are not significant. Hydrates preferentially form on the fracture wall and gradually expand to both the left and right side walls of the fracture. 2. Compared to Type I fractures, in Type X fractures, the hydrate induction time is shorter, and the final formation quantity is larger. Under the condition of a 3 mm fracture width, the induction time decreases by 88.68%. Gas diffuses into the fracture from  
Figure 20: CH\({}_{4}\) consumption curves during hydrate formation in fractures of different widths. multiple directions, leading to a multidirectional centripetal expansion of hydrates in the Type X fractures. * An increase in fracture roughness promotes hydrate nucleation at surface protrusions but inhibits the final quantity of hydrates. In Type I fractures, rough walls significantly shorten the induction time, whereas in Type X fractures, rough walls extend the induction period. * The dissociation of hydrates typically expands from the fracture wall inward, accompanied by a wavy surface topography. Gas production is affected by the fracture width, with the highest observed in the 3 mm fractures, reaching 0.34 mol. * Due to the memory effect, the induction time for hydrate reformation is significantly shorter than that for primary formation, and the formation rate is faster. However, the volume of hydrate reformation is lower than that of primary formation. Therefore, during hydrate extraction, it is crucial to carefully control the temperature and pressure conditions, as well as the dissociation rate, to avoid a rapid decrease in pressure, which may lead to hydrate reformation. In addition to sandy sediments, silty-clayey deposits in submarine fault zones also commonly contain natural gas hydrates. The hydrophilicity, expansibility, and charge properties of silty-clayey zones may influence the growth process and morphology of hydrates in fractures, which could differ from those in sandstone fractures. Future research on the growth of hydrates in silty-clayey fracture zones will be carried out. Furthermore, the diffusion characteristics, solubility, and formation rates of various gases may have distinct effects on the formation and dissociation of hydrates. Future research should further explore other gases, such as CO\({}_{2}\) and hydrogen (H\({}_{2}\)), to advance progress in fields like CO\({}_{2}\) sequestration and H\({}_{2}\) energy development. Similarly, the examination of the impact of fracture orientation on the growth dynamics and morphology of hydrates warrants further investigation [55; 56]. Conceptualization, T.L. ; Methodology, C.M., J.W. and T.L. ; Formal analysis, J.P., T.H. and A.W. ; Writing--original draft, C.M. and X.H. ; Writing--review & editing, H.S., J.W. and T.L. ; Supervision, X.H., H.S. and T.H. ; Funding acquisition, X.H. and H.S. All authors have read and agreed to the published version of the manuscript. This study was supported by the Graduate Innovation Program of China University of Mining and Technology (Grant No. 2025 WLJCRCZL057) and the Postgraduate Research & Practice Innovation Program of Jiangsu Province (Grant No. SJCX25_1377). Not applicable. The original contributions presented in this study are included in the article.