含水合物沉积物相对渗透率研究进展

    Research advances in gas-water relative permeability of hydrate-bearing sediments

    • 摘要: 气-水相对渗透率是天然气水合物现场试采的关键参数。如何测量和评估储层相对渗透率是提高产气效率、实现天然气水合物产业化需要解决的基础问题。从含水合物沉积物相对渗透率的实验测试、数值模拟和模型建立3个方面,总结了含水合物沉积物相对渗透率的研究进展,研究发现,现有含水合物沉积物实验测试大多采用非稳态法,相对渗透率曲线图显示:在同一含水饱和度下,水合物饱和度越大,水的相对渗透率越小,气的相对渗透率变化规律较为复杂;水合物饱和度的变化改变了沉积物的孔隙空间结构,进而影响气-水相对渗透率。数值模拟大多利用孔隙网络模型或持水曲线进行相对渗透率计算,探索水合物生长习性、孔隙赋存特征,并揭示颗粒尺寸、水合物饱和度、润湿性、表面张力等不同因素对气-水相对渗透率的影响差异。梳理多种相对渗透率模型,发现新近提出的考虑毛细作用和孔径分布的含水合物介质相对渗透率模型在模拟含水合物沉积物中的多相流以及解释水合物饱和度的变化方面具有优势。建议下一步克服该模型计算成本较高的缺陷,实现含水合物沉积物多相流物理精确建模。

       

      Abstract: Gas-water relative permeability is a key parameter in the trial production of natural gas hydrate. Measurement and evaluation of the parameter of the hydrate reservoir is essential for enhancing gas production efficiency and realizing the industrialization of natural gas hydrate production. This paper provides a review on the research progress in the relative permeability of hydrate-bearing sediments. It is summarized from three aspects, i.e. experimental measurement, numerical simulation, and model establishment. It is found that the unsteady-state method is widely employed in the permeability measurements for hydrate-bearing sediment. The relative permeability curve suggests that higher hydrate saturation will cause lower water relative permeability at a given water saturation, but the variation of gas relative permeability is complicated; the pore-structure of the sediment changes along with the hydrate saturation, which further results in the changes of gas-water relative permeability. Numerical simulation mostly calculates relative permeability with a pore network model or a water retention curve to explore hydrate growth habits and pore-filling characteristics and the effect of various factors such as particle size, hydrate saturation, wettability, and interface tension and their influence on gas-water relative permeability. A newly developed relative permeability model for hydrate-bearing media considering the influences of the capillarity and pore-size distribution (referred to as RPHCP) is introduced in this work, which shows obvious advantages in simulating the multi-phase flow of hydrate-bearing sediments and explaining the changes of hydrate saturation compared to other models. RPHCP model is recommended to overcome the defect of the high cost of computation of RPHCP model to achieve precise modeling of multiphase flow in hydrate-bearing sediments.

       

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