Numerical simulation of gas production from hydrate-bearing sediments in the Shenhu area by depressurising: The effect of burden permeability

Natural gas hydrates have been investigated as a potential resource for commercially producing gas since the 1990s. Based on the latest available data for the Shenhu area of the South China Sea (SH7), a practical two-dimensional model has been constructed to investigate the gas production potential and the distributions of different physical properties in alternating formations by selecting a proper perforated interval favouring borehole stability and gas production. The effects of overburden and underburden permeability on gas production are intensively discussed. The simulation results indicate that the initial hydrate dissociation mainly occurs among the upper gas hydrate bearing-sediments (GHBS) with a high permeability but that in the later period, it is mainly distributed among the bottom low permeability GHBS. In addition, an obvious hydrate re-formation can be observed in the middle GHBS, and the dilution effect in the bottom low permeability GHBS is stronger than that in the upper space with high permeability. A comparative study showed that the GHBS in the Shenhu area with only one permeable burden (overburden or underburden) is not the most promising target for depressurisation.