An experimental analysis on the elastic mechanical parameters of weakly-consolidated non-diagenetic gas hydrate sediments

Abstract

Gas hydrate (hereinafter, ''hydrate'' for short) in the marine environment mostly lies in weakly consolidated sediments, so its undisturbed coring is difficult and costly. In view of this, it is necessary to understand the relationship between acoustic properties and elastic mechanical properties of hydrates through laboratory experiments. In this paper, samples of hydrate sediments were prepared indoors. Then, petrophysical experiments were carried out on these samples to measure the electric parameters and acoustic parameters of hydrate sediments. Finally, according to the theory of elasticity, the dynamic elastic mechanical parameters under three axial compressions, three particle sizes and three shale contents were calculated to analyze their effects on the dynamic elastic mechanical parameters of hydrate sediments under different conditions. And the following research results were obtained. First, when the hydrate saturation is in a certain range, it is in a proportional relationship with the elastic parameters of sediments. Second, when the hydrate saturation is constant, the dynamic Young's modulus of hydrate sediments increases, but the Poisson's ratio has little to do with the axial compression as particle sizes (0.125–1.180 mm) and axial compression increase and shale content decreases. Third, a model of the relationship between the elastic parameters and the shale content and axial compression is established. In conclusion, the dynamic elastic mechanical indexes of gas hydrate obtained from the acoustic logging methodology will solve the above difficulties and the research results provide a reference for calculating the mechanical properties of hydrate sediments by use of logging data. Keywords: Gas hydrate, Weakly consolidated sediment, Well logging data, Dynamic elastic mechanical parameters, Petrophysical acoustic wave, Particle size, Axial compression