天然气水合物孔底冷冻取样技术及冷冻方式

The research on a sampling technology for gas hydrates by borehole bottom freezing and its freezing method

针对现有天然气水合物保真取样技术的不足,提出了孔底冷冻保真取样技术.分析了孔底冷冻取样方法的几个特点,并基于干冰和液氮2种不同冷源的温压特性,分别对2种冷冻方式的天然气水合物孔底冷冻取样器进行了探讨.数值模拟了在孔深350 m处,钻取天然气水合物岩心并注入冷源后,在孔底冷冻岩心及提升岩心时岩心温度随时间变化的过程,并通过钻探取样试验获得冷冻岩心.结果表明:孔底冷冻取样方法可以实现在孔底冷冻岩心,满足天然气水合物保真取样的要求.

To overcome the shortcomings of truth-sampling technologies for gas hydrates, a truth-sampling technolo- gy based on borehole bottom freezing is proposed. Several major characteristics of the borehole bottom freezing meth- od are discussed in this paper. And taking the temperature-pressure characteristics of the two kinds of cold sources- dry ice and liquid nitrogen as the determination basis, the freezing methods of the two types of freezing core sam- plers （FCS） were studied separately, and the variation of the core temperatures along with the time were simulated during injecting the cold source and lifting the core when the gas hydrate core drilling operation was stopped at the hole＇s depth of 350 m, the freezing samples were achieved during the drilling experiment. The results showed that the sampling method for gas hydrates by use of hole bottom freezing could freeze the sample at the bottom of the hole, and it meets the demands for truth-sampling of gas hydrates.