EXPERIMENTAL STUDY ON GAS HYDRATE SYSTEM STATE EVOLVING DURING DEPRESSURIZATION
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摘要: 天然气水合物是一种重要的潜在替代能源,降压法是现阶段水合物开采的首选方法。水合物降压开采涉及传热、多相渗流、分解相变和储层变形等多个相互影响的物理效应,深入理解其在降压开采过程中的演化规律,对于促进水合物开采效率、实现商业化开发具有重要的指导意义。本文基于一维实验模拟系统,开展了水合物降压开采储层多物理场演化模拟实验,在非均匀温度条件下采用过量气法合成水合物,分析了水合物非均匀性分布特征,探讨了降压过程中样品孔隙压力和温度的演化规律,对比了产气过程与传热演化过程的对应关系。结果表明:水合物合成后温度分布呈两侧高中间低的抛物线形状,水合物分布具有中间多而两侧无的非均匀性特征,且温度回升具有由两侧向中间发展的特点;降压分解产气过程与传热演化过程具有良好的对应性,稳态产气阶段由传热效应控制。控制降压模式、以对流换热替代热传导等方式有益于提升水合物开采产气效率。Abstract: Natural gas hydrate has been treated as a potential energy resource for decades. Depressurization is currently the most promising method for hydrate production. However, its efficiency is far from the commercial need. Hydrate production involves heat transfer, multi-phase seepage, phase transition, and reservoir deformation. A thorough understanding of how multiple physical processes evolve during depressurization is of great significance for efficiency enhancement of hydrate production. An experiment was carried out to simulate depressurization induced evolution of the multiple physical processes. Methane hydrate was formed by using the gas excess method under a heterogeneous temperature condition. Evolutions of pore pressures and temperatures were analyzed. A comparison between gas production process and heat transfer process was discussed. Main conclusions are drawn as follow: temperature distribution is parabola-like after hydrate formation, which has higher temperatures in two sides of the sample. In addition, hydrate distribution is inhomogeneous. Pore pressures decrease completely from the outlet to the inlet, and temperatures increase from the two sides into the middle part. The gas production process related to the heat transfer process well, and the stable stage for gas production is controlled by the heat transfer process. It is a feasible way to replace heat conduction by heat convection or choose a slow depressurization strategy to enhance production efficiency for the commercial need.
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Key words:
- Gas hydrate /
- Depressurization /
- Hydrate saturation /
- Seepage /
- Heat transfer
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表 1 样品三相饱和度求解参数
Table 1. Parameters for calculating hydrate, water, and methane saturations within the sample
参数名称 取值 总进气量Vg*(标准状态SL) 76.7 总进水量mw*/g 500 孔隙度ϕ/% 39.9 样品总体积V/cm3 2826.0 水合物相平衡区域体积V2/cm3 1893.4 左侧水合物非稳定区域体积V1/cm3 310.9 右侧水合物非稳定区域体积V3/cm3 621.7 水合物密度ρh/g·cm-3 0.91* 孔隙水密度ρw/g·cm-3 1 水合物摩尔质量Mh/g·mol-1 119.5* 孔隙水摩尔质量Mw/g·mol-1 18 水合物数Nh 5.75* 气体常数R/J·mol-1·K-1 8.31 气体摩尔体积VSL/SL·mol-1 22.4 孔隙压力Pg1,Pg2,Pg3/MPa 3.54 水合物相平衡区域温度T2/℃ 式(1)且0.11≤x≤0.78 左侧水合物非稳定区域温度T1/℃ 式(1)且0<x<0.11 右侧水合物非稳定区域温度T3/℃ 式(1)且0.78<x≤1 *数值来源于(业渝光等,2011) -
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