人工隔板在海域层系天然气水合物藏降压开采中的适应性分析

Due to the existence of "pressure funnels" formed in reservoirs during depressurization production of marine natural gas hydrate (hereinafter referred to as hydrate) reservoir, a large amount of pore water flows into the wellbore from adjacent layers, resulting in wellbore flooding and consequently hindering the production of hydrate reservoir. Therefore, based on the geological characteristics of hydrate reservoirs in Shenhu sea area of the South China Sea, this paper simulates the 5-year continuous depressurization production process of the marine stratified hydrate reservoir with an artificial barrier by considering the three-phase coexistence system of hydrate, free water and free gas simultaneously. In addition, the wellhead gas/water production characteristics, the pressure/temperature field and the spatial distribution characteristics of hydrate/free water saturation are investigated, and the influence laws of the artificial barrier's radius on the depressurization production performance of hydrate reservoir are analyzed. And the following research results are obtained. First, the wellhead water production rate and cumulative water production in the case of artificial barriers are lower than those without artificial barriers, and especially when the upper and lower barriers (30 m) are laid at the same time, the 5-year cumulative water production at wellhead can be reduced by about 20.88%. Second, the laying of upper and lower barriers can be superimposed in the wellhead cumulative gas increase or water decrease, which means that artificial barriers have a positive effect on the depressurization production of hydrate reservoirs. Third, when the upper and lower barriers are laid simultaneously, the vertical pressure propagation in the sedimentary layer near the laying area can be hindered effectively, and the radial pressure propagation in the sedimentary layer is more uniform in the whole production period. The hydrate dissociation near the end of the barrier is significantly faster than that in the case without barrier, and the layering of the barrier can reduce the effective inflow area of free water near the wellbore. Fourth, as the laying radius of the upper and lower barriers increases from 0 m to 60 m, the 5-year cumulative water production at the wellhead decreases significantly, the composite water cut at the wellhead decreases from 13.45% to 7.8%, and the hydrate dissociation rate increases from 3.84% to 6.32%. In conclusion, the laying of artificial barrier is conducive to the depressurization production of marine stratified hydrate reservoir, but it is still not enough to achieve commercial development only by using artificial barrier combined with depressurization production technologies.