Class 1 hydrate deposits are characterized by a free gas layer beneath the hydrate layer, which are considered as targets with great exploitation potential due to the superior thermodynamic conditions. Low-frequency electric heating technology is very effective in exploiting hydrate deposits because it can avoid the massive heat loss along wellbore in conventional hot water flooding. However, the effect of reservoir properties on gas recovery performance has not been well understood, which challenges the further application of this technology.
In order to reveal the production performance under different property parameters of hydrate layer and gas layer, the geological model of Class 1 hydrate deposits was established based on the data of Messoyakha hydrate field. Considering the current conduction, heat transfer, multiphase multicomponent flow, hydrate phase transition and chemical reaction process in hydrate-bearing porous media, the effects of sediment properties on the gas recovery behavior in the process of low-frequency electric-Joule-heating are studied by numerical simulation method.
The results show that there is no close positive correlation between cumulative gas production and hydrate saturation due to the reverse influence of hydrate resources and effective permeability. With the increase of hydrate saturation, the proportion of energy input by electric heating for hydrate decomposition increases, which improves the energy utilization efficiency. The high permeability of the hydrate layer can enhance the depressurization effect to obtain a higher cumulative gas production, but it reduces the energy utilization efficiency. The amount of gas released by hydrate decomposition increases with the increase of hydrate layer thickness, which can enhance gas production and energy efficiency. Hydrate deposits with high gas saturation show better production performance because of higher gas production rate and energy efficiency. The gas layer permeability has no significant influence on the gas production. When the permeability of gas layer is low, the gas production increases slightly with the increase of permeability, but the energy utilization efficiency is reduced. Hydrate deposits with thicker gas layer thickness show greater production potential, because the cumulative gas production increases approximately linearly with the increase of gas layer thickness, but the energy efficiency of electric heating is not sensitive to gas layer thickness.