天然气水合物孔底冷冻取样方法的室内试验研究

本研究提出的天然气水合物孔底冷冻取样方法是利用外部冷源在孔底降低水合物岩心温度,采用主动式降温的方法降低水合物的临界分解压力,达到被动式降压来抑制水合物分解,获得水合物岩心的方法。首先,通过分析天然气水合物温压特性得出了孔底冷冻取样方法的可行性;然后,借助室内冷冻模拟试验确定了干冰为冷冻剂,酒精作为助冷催化剂和载冷剂的冷冻方式;最后,依据冷冻模拟试验得出的干冰法冷冻方式研制了FCS型天然气水合物孔底冷冻取样器样机,并进行了土层钻进冷冻取样试验,取得冷冻黄土岩心。本研究提出天然气水合物孔底冷冻取样思想,为天然气水合物取样器的设计提供了新的思路。

Laboratory Experimental Study on Sampling Method for Gas Hydrates by Hole Bottom Freezing/

Exploiting gas hydrate is based on the evaluation, and sample drilling is the most direct method. The sampling method for gas hydrate by hole bottom freezing is the way that the temperature of the gas hydrate core is decreased by cold source. Active cooling can reduce the critical dissociated pressure of gas hydrate to inhibit gas hydrate dissociating by passive decompression. The result of temperature decreasing is the same as pressure increasing to retain the core of gas hydrates. But it is easy to decrease temperature of core by external cold source at the well bottom. Firstly, the feasibility of freezing method for sampling gas hydrates is verified by the analysis on the temperature pressure property; secondly, dry ice is confirmed as coolant, alcohol as positive freezing catalyst and cooling medium by means of indoor freezing simulation; and finally, based on the above experiment, the prototype of FCS hole bottom freezing sampler for gas hydrates was developed. Freezing loess sample is achieved by freezing sample experiment. The research puts forward freezing method for sampling gas hydrates, and provides a new idea for the design of gas hydrates core sampler.