Stress behavior of hydrate-bearing sands with changing temperature and hydrate saturation

Abstract

Since the natural gas hydrate (NGH) was confirmed to be widespread in deep-sea strata and permafrost regions, NGH research arouses great enthusiasm among scholars, and the commercial exploitation of NGH also arouses high expectations of the international community. However, from the perspective of safe exploitation, it is necessary to fully understand the mechanical properties of NGH before commercial exploitation. The geological survey shows an apparent temperature gradient in the hydrate reservoir, and the hydrate saturation varies with the reservoir location. Based on the above background, we conducted mechanical experiments on hydrate-bearing samples under different temperatures and hydrate saturation conditions in this work. The data showed that the samples' strength is positively correlated with hydrate saturation and negatively correlated with temperature. The compressibility of the sample is limited by the hydrate solid in the pores. Furthermore, the samples' dilatancy is negatively correlated with temperature and positively correlated with hydrate saturation. From the perspective of experimental phenomena, temperature and hydrate saturation have a coupling effect on the mechanical properties of the samples. With increasing temperature and decreasing hydrate saturation, the stress-strain behaviors of the samples change from softening to hardening. The above experimental results can be attributed to the effect of temperature and hydrate saturation on hydrate cementation structure in pore space. Moreover, the relationship between the stress-strain behaviors and these influencing factors was established. According to the above results, the existing constitutive model of hydrate-bearing samples can be improved. The accuracy of stability analysis of hydrate reservoirs can also be improved, which provides a theoretical basis for the safe exploitation of hydrate resources.