A model-based study of the evolution of gravel layer permeability under the synergistic blockage effect of sand particle transport and secondary hydrate formation

When using gravel-packed completions to exploit hydrates, the synergistic blockage of gravel filling layer by sand and hydrate often arises. In this paper, we completed two kinds of permeability measurement experiments: experiments with different volume proportions of sand particles and experiments with different hydrate saturations in the pores of gravel filling layer. The variation in the permeability of a gravel filling layer under the simultaneous blockage due to small sand particles invasion and hydrate formation was studied experimentally. Based on the different assembly forms of spherical particles and classic permeability theory models, this paper first established an experimental model of the permeability of gravel filling layer formed by the secondary formation of hydrates under different sand volume proportions. Second, this paper analyzed the permeability measurement data. A modified permeability model based on the synergistic blockage mechanism of sand and hydrate in the gravel filling layer was obtained. Finally, this study revealed the permeability evolution of the gravel filling layer under sand intrusion and hydrate formation. The experimental data and permeability theory model results supported the following conclusions: (1) The assumption of sand particles gathering in clusters in the pores has a similar impact on permeability as the formation of hydrates at the center of the pores, resulting in an exponential decrease in permeability as the proportion of sand particles increases. (2) Based on the changes in the surface areas of pores in a gravel filling layer during the processes of sand intrusion and hydrate growth, a theoretical model of the relative permeability of gravel filling layer was established. (3) Analyzing the permeability measurement experimental data revealed that the presence of small sand particles in the experiment was more conducive to the formation of hydrates, and a high saturation of hydrates may have formed in some areas, leading to more serious blockages in the gravel filling layer. This study validated the effectiveness of the theoretical model of relative permeability through permeability measurement experiments and explored the mechanism of cooperative sand and hydrate plugging, providing a theoretical basis for the safe and efficient exploitation of hydrate reservoirs.