Physical And Mechanical Properties Research On Natural Gas Hydrate Bearing Sediments

In the increasingly serious energy crisis of the 21st century, natural gas hydrate is recognized as an important development prospect with good follow-up of energy, Natural gas hydrate is a kind of new clean energy with high efficiency and huge amounts deposits. Natural gas hydrate distributes mainly in the marine continental margin sediments and permafrost environments, the former account for about 90% of the number have been found. Currently, commercial exploitation of gas hydrates has been included in the agenda of many countries. Ensuring the stability of the borehole is the key to the success of drilling in the gas hydrate sediments and the going on wheels of the whole exploration plan, Physical and mechanical properties of gas hydrate studies is the basic to study about the well bore stabilityThe development of triaxial compression apparatus for gas hydrate sediment can carry out triaxial test and acoustic test, which is the biggest advantage of the system. Coated sand in the laboratory was sintered into the host specimen, and then synthesized of different saturation methane hydrate bearing sediments by using the in situ method. A series of triaxial shear tests were carried out on artificial methane hydrate bearing sediments with different methane hydrate saturation and confining pressure. The preliminary results show that with the increasing of confining pressure and methane hydrate saturation, the peak strength was enhanced, with the increasing of saturation cohesion also increased, but modulus of elasticity and poisson ratio have not remarkable changed, according to the experimental result we build the mathematical model to the peak strength of different methane hydrate saturation and confining pressure; according to the experimental results we also established the strength failure criteria of hydrate sediment layer, which can lay foundations for the sequential studies of hydrate layer's well bore stability. For comparison experiments, a series of ice,tetrahydrofuran(THF) hydrate sediment triaxial tests were carried out according to the experimental methods of methane hydrate bearing sediments, founding that the mechanical properties of ice,THF hydrate and methane hydrate bearing sediments were not very different.In this paper, acoustic wave tests were did under different confining pressure for different saturation of methane hydrate bearing sediments,THF hydrate sediments and ice bearing sediments, which were synthesized in situ. According to elasticity theory, using the measured ultrasonic wave velocity, we calculated the dynamic elastic mechanical parameters of the samples. The results show that: P waves and S waves increased with the confining pressure and saturation increasing, the dynamic elastic modulus increased with the confining pressure and saturation increasing. The experimental data and conclusions of this paper will give some supports in the exploration of hydrate bearing sediments and the evaluation of resources.