Experimental Study on Mechanical Properties of Artificial Cores Saturated With Ice: An Analogical Simulation to Natural Gas Hydrate Bearing Sediments

Abstract

This work takes the natural gas hydrate (NGH) reservoir in the Shenhu area at the South China Sea as the target. Using the quartz sand, calcite grains, and illite powder as the main mineral composites, and Portland cement as the bonding material, the host skeleton with similar porosity and mechanical properties to the target reservoir were prepared. Ice was used to simulate natural gas hydrates for their high similarity in mechanical properties and distributions within porous host. The ice saturation in the host skeleton is quantitatively controlled by the quality method. As an analogical simulation, artificial samples with different ice saturations were tested by uniaxial compression measurements and the Brazilian tensile tests, aiming to reveal the mechanical behavior of NGH sediments. The results indicated that the plasticity of the artificial sample increases and its damage form transitions from brittleness to ductility as the ice saturation increases. The effects of free water and ice on the strength of saturated samples are quite different. The free water tends to reduce the strength of the sample due to illite hydration and change of internal friction. The bonding effect of ice tends to increase the strength of the sample, while the ice could also reduce the internal friction. When the ice saturation is larger than 30%, the compressive and tensile strengths of the sample increase with ice saturation, which could be regressed as y_c = 2.2628S + 0.8322, and y_t = 0.411S + 0.0273, respectively. The constitutive model was developed based on the equivalent medium theory and the D-P criterion, which could describe the experiment data well with deviations less than 10%.