Study on the Influencing Factors of Reservoir Sand Production and Permeability during Hydrate Depressurization Exploitation

Sand production in the reservoir is a key issue restricting the safe exploitation of natural gas hydrate, and reservoir permeability is a key parameter affecting the production capacity of hydrate exploitation. The effects of particle size distribution of reservoir, hydrate saturation, depressurization amplitude and pore size of sand prevention layer on reservoir sand production and permeability during hydrate depressurization exploitation were investigated by laboratory model tests. The correlation between the reservoir sand production and change in reservoir permeability was analyzed. The results show that: (1) Factors influencing reservoir sand production: the lower the clay content, the larger the depressurization amplitude, and the greater the pore size of sand prevention layer were, the larger the amount of reservoir sand production. With the same pore size of sand prevention layer, the amount of reservoir sand production has approximately a linear relationship with the average flow rate of water. (2) Factors influencing reservoir permeability: the reservoir permeability generally increased with time, and finally gradually tended to a stable value. The greater the hydrate saturation, and the greater the clay content were, the smaller the initial value of permeability. The greater the depressurization amplitude, and the larger the pore size of sand prevention layer were, the greater the ratio of final value to initial value of permeability. (3) The correlation between the sand production and variation in permeability: with the same hydrate saturation, the more the amount of reservoir sand production was, the relatively greater the increase amount of reservoir permeability. With the same hydrate saturation and particle size distribution of reservoir, the more the amount of reservoir sand production was, the relatively greater the increase rate of reservoir permeability.