Study On Hydrate Morphology And Adhesion Characteristics On Mineral Rock Surface

Natural gas hydrates are ubiquitous in the world,and are mainly concentrated in the extremely cold permafrost zones,the polar continental shelf,the gravel of the continental slope,the bottom of the deep sea,and the fracture pores of the sediments at the bottom of the deep lake.It has a huge amount of resources and it’s an environmentally friendly renewable energy source with the most development value.At present,most scholars use sand-filled tubes and cement cores to simulate the formation environment to explore the growth process of hydrates.However,these studies can not be visualized and can not directly reflect the nucleation and growth process of hydrates.In addition,the analysis of the adhesion mechanical properties of natural gas hydrates on rock mineral surfaces can accurately evaluate and effectively control the influence of hydrates in the sedimentary layer,which is an important link in the hydrate mining process.In this paper,the hydrate formation device in the visible microscopic pore structure of hydration reaction under normal pressure was constructed.The growth morphology and formation law of cyclopentane hydrate were observed experimentally,and the influencing factors of hydrate formation rate were explored.In addition,the experimental device for hydrate wall adhesion test under liquid and gas phases was constructed.The effects of factors such as subcooling,hydrate formation time,rock wall microstructure and rock mineral types on adhesion were investigated,and theoretical results were analyzed.Finally,a critical flow velocity model was constructed to analyze the critical flow velocity of the fluid when the hydrate was driven away and the CFD technology was used to simulate the phenomenon of fluid pushing hydrates.The relationship between the hydrate adhesion strength and the critical flow velocity of the fluid was analyzed by simulation,and the influence of the change of the thickness and length of the hydrate layer on the critical flow velocity of the fluid was explored.The results show that the hydrate is formed at the interface of the two phases first,gradually covering the water film,and then extending laterally until a thin crystal shell is formed,which grows laterally thicker and finally growing in a cluster shape toward the cyclopentane.The greater the curvature of the water film,the more the amount of hydrate formed by the reaction at this point,the thicker the hydrate accumulation.Larger subcooling and a certain amount of surfactant can accelerate the growth rate of hydrate,and the growth rate of hydrate shows a trend of slowing down gradually.In addition,increasing the formation time of hydrate,increasing the degree of subcooling during hydration reaction,more obvious wall microstructure and better wettability can increase the adhesion between hydrate and rock wall.For thinner hydrate layers grown on the wall,the cross-section and the hydrostatic force are less affected,so a larger critical velocity of the fluid is required to drive away than the thicker hydrate layer.When the hydrate layer is longer,the contact area with the wall surface increases,and it has stronger adhesion.Therefore,the critical flow velocity of the fluid increases as the length of the hydrate layer increases.