Numerical simulation on gas production from hydrate reservoir at the 1st offshore test site in the eastern Nankai Trough

• A model matching the 1st offshore hydrate production test was built.
• The long-term production simulations were performed based on the short-time data.
• The significance of sediment-hosted hydrates below the bottom hole was reported.
• Effect of completion interval on gas recovery from hydrate deposit was fully studied.

According to the available geological data of hydrate reservoir at the 1st offshore production site in the Eastern Nankai Trough in 2013, a simulation model matching the production test scheme was established to investigate a relatively long-term production performance and the effect of perforated interval on gas production by comparing the short simulation results and the field test data (6 days). The verification results indicate that the simulated gas production rate is consistent with the measured field value but a certain deviation of corresponding water production rates occurs. The relatively long-term simulation performed reveal that both gas released rate in the sediment and gas production rate in the well increase before complete dissociation of hydrates between bottom hole and underburden. After that, they convert to decreasing and the water production rate increases sharply. Meanwhile, the slight secondary hydrates are observed in the dissociation front. Additionally, the sensitivity analysis of completion interval indicates that the perforated interval design for candidate hydrate reservoir like this site should avoid the low-permeability hydrate layer and take the lower hydrate layers as the water blocking zones when using depressurization method, and that the optimum completion interval should be determined by together considering the production period and the expected production rate.