Numerical evaluation on the effect of horizontal-well systems on the long-term gas hydrate production behavior at the second Shenhu test site

Abstract In 2019–2020, the second natural gas hydrate field trial was successfully performed in the Shenhu Area of the South China Sea by using a horizontal well, however, the long-term production performance is unclear and needs intensive surveys. In this work, a multilayered hydrate reservoir model was constructed to replicate the short-term test result on the basis of the field data obtained at this site for the first time. Then, the long-term gas hydrate production behaviors at this site by using the single-horizontal-well and dual-horizontal-well systems were investigated, and the production strategy of thermal stimulation was proposed to examine the effects of the injection parameters of the hot water on the enhanced gas recovery. From the analysis of the simulation results, it can be known that due to the extremely low permeabilities of the whole reservoir (2.38–6.8 mD), the 10-yr average gas production rates (7.71 × 102–2.88 × 103 m3/d) could only reach 1/10 of the level obtained in the second Shenhu field trial (2.87 × 104 m3/d), which indicated that none of the above methods were quite suitable for future commercial gas production at this site. Therefore, it is recommended that permeability enhancement should be implemented in advance to improve the reservoir permeability before the actual long-term gas production.