多孔介质中天然气水合物生成的主要影响因素

Major factors influencing the formation of natural gas hydrates in porous media

目前有关天然气水合物(以下简称水合物)的研究主要集中在物理化学性质考察和开采(分解)方法探索方面。在进行后者的研究过程中,地层渗流过程的物理模拟至关重要,但目前借助于石油开采研究中广泛应用的填砂管等多孔介质对水合物进行动态过程的研究却鲜有报道。为此,利用河砂填砂管在岩心驱替装置上进行了甲烷水合物生成过程的物理模拟,考察了地层温度、甲烷压力及地层模型性质参数等对水合物生成过程的影响。结果表明:(1)利用冰融水作为地层模型的束缚水可显著提升甲烷水合物的生成速率;(2)多孔介质条件下过程驱动力(即实验压力或温度偏离水合物相平衡对应值的程度)对甲烷水合物的生成起着决定性作用;(3)当甲烷压力高于水合物相平衡压力1.4倍以上,或者实验温度低于相平衡温度3℃以下时,甲烷水合物生成诱导期几乎不随温压条件的变化而变化;(4)渗透率、含水饱和度、润湿性等参数对实验中甲烷水合物的生成率不构成明显影响。

Current researches related to natural gas hydrate mainly focus on its physical and chemical properties, as well as the approach to the production （decomposition） of hydrates. Physical modeling of the seepage process in hydrate deposits is critical to the study on the exploitation or decomposition of hydrates. However, investigation of the dynamic hydrate process by virtue of porous medialike sandpacked tubes which are widely used in petroleum production research is rarely reported in literatures. In this paper, physical modeling of methane hydrate generation process was conducted using river sandpacked tubes in the core flooding apparatus. During the simulation, the influences of parameters such as reservoir temperature, methane pressure and reservoir model properties on the process of hydrate generation were investigated. The following results are revealed. First, the use of ice-melted water as the boundwater in the reservoir model can significantly enhance the rate of methane hydrate generation. Second, the process driving force in porous media （i.e., extents to which the experimental pressure or temperature deviating those corresponding to the hydrate phase equilibrium） plays a key role in the generation of methane hydrates. Third, the induction period of methane hydrate generation almost does not change with temperature or pressure when the methane pressure is above 1.4 folds of the hydrate phase equilibrium pressure or the laboratory temperature is lower than the phase equilibrium temperature by 3℃ or more. Fourth, the parameters such as permeability, water saturation and wettability don＇t have much influence on the formation of methane hydrates.