天然气水合物下伏游离气垂直单井开发数学模型及其应用

天然气水合物下伏游离气是水合物系统天然气资源的重要组成部分，具有巨大的开发利用价值。通过构建水合物下伏游离气藏垂直单井开发的数学模型，用有限元节点上的气体密度和密度增量来计算天然气开发中气藏压力变化和井孔气体产能。利用Dako试验气田的产能记录对模型进行了验证，反映了其良好的可靠性。模型显示气体产能与气藏压力、气体饱和度以及采气时间都有很好的正相关，而气体累计产量与采气时间呈近似线性关系，降低井孔流体输出压力有利于提高产能。模拟计算表明布莱克海台水合物下伏游离气藏具有很高的开发价值，对于平均气体饱和度为20％的气藏，计算的单井产气率为46％，69 m厚的气层10 a可产天然气9.6×10⁴ t。

A numerical model for vertical single well production from free gas zone beneath the hydrate layer: Case history of the Blake Ridge

The free gas zone beneath the hydrate layer is an important part of methane gas hydrate resources with a big potential of recovery and exploitation. This paper built up a numerical model for vertical single well production from free gas zone beneath hydrates, in which the reservoir pressure and well productivity at any node of finite element were explicated by gas density and density increment at the point. We used the production data of the Deko trial gas reservoir in the U. S. A. to test this model and found out a good reliability supporting this model. The computation showed that gas production ability had positive correlation with reservoir pressure, gas saturation and exploiting time, and the accumulative gas production had almost linear relation with the time span. The numerical computation also demonstrated that the gas reservoir beneath the hydrates at the Blake Ridge was of great development value by an example of a gas reservoir with the thickness of 69 m under the hydrate layer which was estimated to produce 96 thousand tons of gas accumulatively in ten years in the case of gas saturation of 20% on average and the calculated gas production rate of a single well being 46%.