天然气水合物降压分解过程的数值模拟

Numerical Simulation of the Decomposition of Natural Gas Hydrates by Depressurization

刘建军 邵祖亮 郑永香

LIUJianjun SHAOZuliang ZHENGYongxiang

"油气藏地质及开发工程"国家重点实验室·西南石油大学, 四川 成都 610500 西南石油大学地球科学与技术学院, 四川 成都 610500

State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China School of Geoscience and Technology, Southwest Petroleum University, Chengdu, Sichuan 610500, China

天然气水合物分解是一个复杂的相变传热传质过程。在考虑热传导、热对流、气液两相渗流和水合物分解动力学等因素的情况下，建立了天然气水合物降压分解的三维数学模型。应用数值模拟的方法，分析了井底压力、水合物初始饱和度和储层绝对渗透率对分解的影响。结果表明，井底压力越小，水合物分解越快，储层温度和压力下降也越快；水合物的初始饱和度较大时，前期分解速度较快，后期分解速度变慢，过高的初始饱和度反而会抑制水合物的分解；渗透率对产气量影响不大，但当渗透率过低时，采用降压法开采的生产效率较低，可以考虑降压法与其他方法结合使用。

Natural gas hydrate decomposition is a complicated process involving heat and mass transfer and phase transitions. We established a three-dimensional mathematical model for the gas hydrate decomposition by depressurization taking factors such as heat conduction, heat convection, gas-liquid two-phase flow, and hydrate decomposition kinetics into consideration. The effects of the bottom hole pressure, initial hydrate saturation, and absolute permeability of the reservoir on the decomposition results were analyzed using numerical simulation. The results showed that the lower the bottom hole pressure is, the faster are the gas production rate and the reservoir temperature and pressure decrease. When the initial saturation of the gas hydrate is relatively large, the decomposition rate of the early stage is faster, but that of the later stage is slower. When it is too high, it will inhibit the decomposition of the gas hydrate. The absolute permeability has little impact on the gas production; however, when the permeability is too low, the production efficiency will be lower. Therefore, a combination of the depressurization method and other methods can be used.

10.11885/j.issn.1674-5086.2016.06.09.01