Study On Creep Properties Of Methane Hydrate And Sediments

Natural gas hydrate is recognized as an important follow-up energy in the21st century, which has drawn much attention by more and more countries. However, the natural gas hydrate may dissociate when we explore the deposits, which may result in geological disasters such as submarine landslides and tsunamis. Currently many institutions have been researching the mechanical properties of methane hydrate, but there are few researches on the creep properties. Thus it is essential to determine creep properties of methane hydrate and sediments.In this dissertation, the main researches and conclusion are as follows:A series of creep tests were performed to study the creep properties of methane hydrate containing ice under different temperatures, confining pressures and axial stresses. The effect of temperature, confining pressure and axial stress on axial strain and creep rate were analyzed. The result shows that the axial strain and creep rate of methane hydrate containing ice increases with the increase of temperature and axial stress, while it decreases with the increase of confining pressure. The creep rate of methane hydrate containing ice changes linearly with the change of axial stress and confining pressure, while it changes non-linearly with the change of temperature, and the creep rate grow faster when the temperature was close to0℃.A series of creep tests were performed to study the creep properties of methane hydrate-bearing sediments under high-level stress, low-level stress and various stress. The effect of temperature, confining pressure and axial stress on axial strain and creep rate were analyzed. The result indicates that Φ60(porosity is60%) methane hydrate-bearing sediments show attenuation and some viscoelastic even they are destroyed, the temperature and confining pressure will change the creep curves a lot under high-level stress. The axial strain and creep rate of Φ60methane hydrate-bearing sediments increases with the increase of temperature and axial stress, while it decreases with the increase of confining pressure under low-level stress. Under variable stress conditions, the creep curves got into a new round of damping creep stage and isokinetic creep stage when the axial stress was changed, and the difference between it and constant axial stress curve became more and more.Based on the creep curves of methane hydrate containing ice and methane hydrate-bearing sediments, this paper proposes the axial strain-dependence curves of axial stress at various moments. The result indicates that the creep curves in this research show attenuation, which results in the attenuation of axial strain-dependence curves. The variable modulus decreases with the increase of time. The strengthen coefficient does not change with the increase of time. The strengthen coefficients of the methane hydrate containing ice are larger than the methane hydrate-bearing sediments’, but become smaller gradually as time increases. The strengthen coefficients of methane hydrate containing ice are larger than the methane hydrate-bearing sediments’.Various proportion of kaolin clay and methane hydrate were mixed together to get methane hydrate-bearing sediments with various porosity. The effect of porosity on the methane hydrate-bearing sediments was analyzed. It indicates that the axial strain and creep rate decrease with the increase of porosity.