一种冻土区天然气水合物地球化学勘查新技术——惰性气体氦氖分析

开发不受沼泽微生物影响的地球化学勘查技术是提高中纬度冻土区天然气水合物探井预测成功率的重要课题之一。本文选择在祁连山聚乎更天然气水合物已知区进行惰性气体勘查技术实验,研究了氦氖的测试方法,实验区为高寒沼泽景观,面积150km~2,采样密度2点/km~2,采样深度60cm,采集土壤顶空气样品300件和DK-3井岩芯样品400件,应用色谱反吹技术对顶空气样品进行了惰性气体氦氖的分析。结合地质和地球化学勘查成果进行了综合解释,认为惰性气体异常与天然气水合物矿藏关系密切,与烃类异常浓度范围一致,为顶部异常模式。实验区天然气水合物矿藏11个水合物发现井有10个位于He、Ne异常内,1个井位于异常外。分析了天然气水合物岩芯顶空气轻烃和氦氖指标的垂向分布特征,提出了天然气水合物矿藏上方土壤惰性气体的地气迁移机理。研究区近地表氦氖异常源于深部水合物矿藏和断裂构造,不受沼泽微生物的影响,是冻土区天然气水合物勘查的一种有效技术。

A new tool for natural gas hydrate exploration in permafrost regions:analysis of inert gas helium neon

The development of geochemical exploration technologies unaffected by marsh microorganisms isone of the important issues to improve the prediction and exploration for natural gas hydrates in mid- latitude permafrost areas. The potential of inert gases as a new tool for the investigation of gas hydrates in permafrost areas using He and Ne test methods was investigated in this paper. The study area with a size of 150 km2 is located in the alpine arctic swamp landscape of the Qilian Mountains. The sampling density and depth are 2 points/km2 and 60 cm, respectively. In total, 300 headspace gas samples and 400 core samples were collected and the chromatographic backflush technique was used to analyze the inert gases (helium and neon) in the headspace gas samples. Combined with the comprehensive interpretation of geological and geochemical exploration, our study indicates that the anomalies of inert gases have close relationship to natural gas hydrate reservoir, and are within the range of hydrocarbon anomalous concentration, suggesting an atop anomalous mode. Ten of the 11 gas hydrate wells discovered in the experimental area of Juhugeng are located within the anomalious area of He and Ne; only one well is outside of the anomalous area. This study analyzed the vertical distribution pattern of light hydrocarbon, helium, and neon in the headspace gas of hydrate drilling. We propose a geogas migration mechanism of inert gases in the soil above the natural gas hydrate deposits. The He and Ne anomalies near the ground surface of the Muli coalfield in the Qilian Mountains, derived from the deep hydrate deposits and fault structure, are not affected by marsh microorganisms; they are the effective tools for natural gas hydrate exploration in permafrost areas.