Gas-hydrate saturation and porosity are the most crucial reservoir parameters for gas-hydrate resource assessment. Numerous academics have put forward elastic and electrical petrophysical models for calculating the saturation and porosity of gas-hydrate. However, owing to the limitations of a single petrophysical model, the estimation of gas-hydrate saturation and porosity using single elastic or electrical measurement data appears to be inconsistent and uncertain. In this study, the sonic wave velocity, density and resistivity well log data are combined with a Bayesian linear inversion method for the simultaneous estimation of gas-hydrate saturation and porosity. The sonic wave velocity, density and resistivity data of the Shenhu area in the South China Sea are used to estimate the gas-hydrate saturation and porosity. To validate the accuracy of this method, the estimation results are compared with the saturation obtained from pore water chemistry and porosity obtained from density logs. The well log data examples show that the joint estimation method not only provides a rapid estimation of the gas-hydrate reservoir parameters but also improves the accuracy of results and determines their uncertainty.

The natural gas hydrate has been regarded as an important future green energy. Significant progress on the hydrate exploitation has been made, but some challenges are still remaining. In order to enhance the hydrate exploitation efficiency, a significant understanding of the effective thermal conductivity (ETC) of the hydrate-bearing sediment has become essential, since it directly controls the heat and mass transfer behaviors, and thereby determines the stability of hydrate reservoir and production rate. In this study, the effective thermal conductivities of various hydrate-bearing sediments were in-situ measured and studied. The impacts of temperature, particle size and type of sediment were investigated. The effective thermal conductivities of the quartz sand sediments before and after hydrate formation were in-situ measured. The results show the weak negative correlation of effective thermal conductivity of the quartz sand sediment on the temperature before and after the hydrate formation. The effective thermal conductivity of the hydrate-bearing sediment decreases with the increase of particle size of the sediment. The dominant effect of the type of porous medium on the characteristics of the effective thermal conductivity of hydrate-bearing sediment was highlighted. The results indicate that both the effective thermal conductivities of hydrate-bearing quartz sand sediment and hydrate-bearing silicon carbide sediment are weakly negatively correlated with temperature, but the effective thermal conductivity of hydrate-bearing clay sediment is weakly positively dependent on the temperature. In addition, the values of the effective thermal conductivities of various hydrate-bearing sediments are in the order of hydrate-bearing silicon carbide sediment > hydrate-bearing quartz sand sediment > hydrate-bearing clay sediment. These findings could suggest that the intrinsic thermal conductivity of porous medium could control the characteristics of effective thermal conductivity of hydrate-bearing sediment.