Study On Mechanical Properties And Influencing Factors Of Sand Containing Tetrahydrofuran Hydrate

In recent years,natural gas hydrate(NGH),has becomed the new replaceable energy with attracted much attention,and many countries have listed NGH as the national strategy.China also has made NGH as one of the key development directions,and launched two rounds of field trials on NGH exploitation in Shenhu area of South China Sea.With the process of NGH exploration and exploitation,destroy the gas hydrate equilibrium will cause the NGH decomposition and change the mechanical structure of the original hydrate-bearing sediment,which may lead to a series of problems such as well kick,blowout,reservoir deformation,large sand production and wellbore collapse.Meanwhile,there is meaningful to research the mechanical properties in hydrate-bearing sediments.For the tetrahydrofuran hydrate(THF),there is a remarkable resemblance between it and natural gas hydrate.The tetrahydrofuran solution can be miscible with water at any ratio,which forms the THF only at atmospheric pressure and 0 ? 4 ?,and the THF can be evenly distributed in the samples.Consequently,it is mainly used to research the mechanical property in the hydrate-bearing sediments.Firstly,according to the synthetic method on THF,this paper analyzes and verifies the problems as the temperature control during these tudies,the presence with THF in the samples,and the unfreezing time of THF samples.Then,according to the research on the THF samples,the influencing factors,which are THF saturation,sample particle diameter and distribution state of THF,are determined as the research targets.The test results mainly include:(1)For sediment samples containing cemented tetrahydrofuran hydrate,it is confirmed that the increase of the THF saturation and the particle size will lead to the increase of the yield strength,peak strength,initial elastic modulus and secant modulus;(2)For sediment samples containing cemented tetrahydrofuran hydrate,the internal friction angle of the sample has little relation with the THF saturation,but increases with the increase of the particle size.The cohesion of the sample increases with the increase of the THF saturation,but has little relation with the particle size;(3)For THF samples with different particle size and hydrate saturation,when the saturation of samples is low,the sample strength is dominated by sediment particles,and for sediment particles with smaller particle size,the greater the sample strength is;when the saturation of samples is high,the sample strength is dominated by hydrate saturation,and for larger sediment particles,the greater the sample strength is;(4)For sediment samples containing non-cemented tetrahydrofuran hydrate,it is slow rise with broken line in the initial stage of compression,and the peak strength of the sample is significantly lower than that of the sample with cemented hydrate.The effect of the THF saturation on the cohesion of the sample is small,but the internal friction angle of the sample increases with the increase of the THF saturation.