Rock-physics modeling for the elastic properties of gas hydrate-bearing sediments under varying fluid saturation and temperature

Abstract

The microscale physical properties of gas hydrate-bearing sediments (HBSs) are significant for understanding their macroscale elastic responses and further facilitating seismic exploration. Several models have been developed to investigate the microscale properties of gas HBSs, whereas most of them place emphasis on the construction of the rock frame, ignoring the influence of mixing patterns of pore fluids. Based on laboratory observations, we have developed a rock-physics model that integrates the spatial distribution of gas hydrate, water, and free gas in pores; in addition, this model considers the variable stress-strain relationship of the pore fluids depending on hydrate saturation. We also attempt to incorporate the effect of temperature on the elastic properties of gas HBSs through theoretical modeling. Our approach of handling hydrate-gas spatial relationship reasonably delineates the velocity trends, ensuring that prediction results are congruent with field data. Moreover, the variable stress-strain relationship of the pore fluids allows for the achievement of better simulation results than those by conventional iso-stress and iso-strain fluid mixing schemes. Integrating the factors tied to hydrate dissociation and hydrate moduli reduction during heating processes enables the prediction of a declining trend in the velocity-temperature relation, which is congruent with laboratory-measured data. This model provides an alternative approach to predict the elastic properties of gas HBSs and can reasonably explain the effects of fluid saturation and temperature.