Formation conditions of gas hydrates in permafrost of the Qilian Mountains, Northwest China.
Formation conditions of gas hydrates in permafrost of the Qilian Mountains, Northwest China.
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发表时间：
2006
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通讯作者：
Zhang Yong-qin
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作者：
Zhang Yong-qin
祁连山多年冻土面积约10万km2，年平均地表温度在-1.5 ~ -2.4℃之间，多年冻土厚度在50 ~ 139 m之间。祁连山地区侏罗系小含煤盆地分布广泛，含煤层气丰富。南祁连盆地是一个潜在的含油气盆地，区内有下石炭统丑牛沟组、下二叠统曹地沟组、中三叠统大家连组和上三叠统加勒德西组4套烃源岩，均具有较高的成烃潜力。木里煤田33孔多年冻土带内发现烃气连续逸出。当我们点燃井口时，逸出的气体燃烧起来。简单气样分析表明，甲烷含量高达38.07-75.9%。综合33孔天然气成分、年平均地表温度、多年冻土厚度及热梯度，认为33孔多年冻土主要具备天然气水合物形成的温压条件。计算表明，水合物稳定带可能出现在171 ~ 574 m区间，厚度为403 m。
Permafrost in the Qilian Mountains covers an area of about 100000 km2 with an annual mean ground surface temperature ranging from -1.5 to -2.4℃ and permafrost thickness ranging from 50 to 139 m. Small Jurassic coal-bearing basins are widespread in the Qilian Mountains, which contain abundant coal bed methane. The South Qilian basin is a potential petroleum-bearing basin, where there are four suites of hydrocarbon source rocks, namely, the Lower Carboniferous Chouniugou Formation, Lower Permian Caodigou Formation, Middle Triassic Dajialian Formation and Upper Triassic Galedesi Formation, which all have a high genetic potential. Continuous escape of hydrocarbon gases was found inside the permafrost interval at hole 33 in the Muli coal field. When we ignited the wellhead, the escaping gas burned. Simple gas sample analysis shows that it contains as high as 38.07-75.9% methane. Based on the gas composition, annual mean ground surface temperatures, permafrost thickness and thermal gradients of hole 33, the permafrost in the main has the temperature-pressure conditions for the formation of gas hydrates. Calculation indicates that the hydrate stability zone probably occurs in the 171-574 m interval with a thickness of 403 m.