Meso-mechanism of weakening characteristics of interface between gas hydrate-bearing sand and mining well under cyclic shear
Rock formation with gas hydrate-bearing sands exhibits features of shallow burial,unformed rock and low strength.The weakening characteristic of the interface between gas hydrate-bearing sand and mining well under wave cyclic loading are significant and can directly affect the wellhead stability.In this study,the cyclic shear mechanical properties of the interface between gas hydrate-bearing sands and mining well were investigated based on a discrete element method(DEM).By setting the wellbore motion caused by wave cyclic loading,the macroscopic weakening mechanism of the interface was revealed from a mesoscopic perspective.The results show that the gas hydrate-bearing sand can cause a significant strength weakening and shear dilation at the interface between gas hydrate-bearing sands and mining well,and the higher the gas hydrate saturation,the more significant the weakening and shear dilation.The reason is that the near-wellbore gas hydrate-bearing sands can form a cementation failure zone under cyclic shear,where the cementation of most particles could be failed,while a few gas hydrate particles that might not failed to cement could form larger size clusters with neighboring particles,but these particles and clusters tumble and move complexly which cannot adequately transfer loads,resulting in strength weakening and shear dilation.Increase of both normal stress and shear amplitude can aggravate the cementation failure of the near-wellbore gas hy-drate particles,and the strength weakening phenomenon can be more severe.
interface between gas hydrate-bearing sand and mining wellcyclic shearinterface weakeningcementationdiscrete element method
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