天然气中稀有气体浓度与同位素比值联测技术及应用

研制了天然气中稀有气体纯化富集的前处理装置，并与稀有气体同位素质谱仪联用，构建了气体样品中He、Ne、Ar、Kr、Xe浓度和同位素比值联测的分析系统，通过1次进样可得到5种稀有气体组分浓度和同位素比值的共计23个数据。稀有气体纯化效果可达99.9%，质谱分析He、Ne、Ar、Kr浓度的相对标准偏差小于10%，同位素比值分析的标准偏差普遍小于5%。将该方法用于分析塔里木盆地天然气样品，得到了丰富的地质地球化学信息，通过稀有气体分布特征进一步明确了塔河和雅克拉气田区域构造活动的差异，以及二者气源岩特性的不同。

Analysis of Concentration and Isotope Ratio of Noble Gases in Natural Gas

Natural gas contains a large amount of hydrocarbon gases but only trace amount of noble gases. To measure concentrations of noble gases in natural gas, the active gas components (CH₄, C₂⁺, CO₂, etc.) have to be previously removed. The device of noble gas analytical system was designed for the purification and enrichment of noble gases in natural gas, and their element and isotope ratio were analyzed by quadrupole mass spectrometry and isotopic mass spectrometry, respectively. Dynamic vacuum of this system was better than 1.0×10^-6 Pa. The natural gas was firstly introduced to the analytical system and then exposed to a Zr-Al purifying furnace (held at 350 ℃) for 20 min, during which the hydrocarbons, CO₂ and other active gases could be absorbed, aliquot of purified noble gases were transfered to the gas getters for the second purification (10 min), then ⁴He, ²²Ne, ⁴⁰Ar, ⁸⁴Kr, ¹³²Xe were measured by QMS. At last, separation of He+Ne, Ar and Kr+Xe were basically successful by temperature modulated cold finger, and then noble gases isotopic compositions could be measured. Because the noble gases concentration and isotopic ratio in air were well determined, the air could be employed as a standard sample to determine. The degree of purifying noble gases can reach to 99.9%. The relative standard deviation of He, Ne, Ar, Kr content measured by QMS is less than 10%, isotope ratio has a better accuracy generally less than 5%. Although noble gases are ubiquitous in natural gas, they are more accurate and sensitive than stable carbon isotopes for tracing hydrocarbon formation and evolution because of the chemical inertness and time-accumulating effect. However, isotope compositions of noble gases have only been previously used to study tectonic movements, the age of source rock, and terrestrial heat flow, concentration of noble gases, which is good at determining the geochronology of hydrocarbon accumulation, has not yet been published to our knowledge due to the restriction of analysis method. This analytical technique established for noble gases in natural gas could provide abundant geological and geochemical informations containing 23 data about concentration and isotope composition of He, Ne, Ar, Kr, Xe, which will be a powerful tool for studying the geochemistry of natural gas. Natural gas samples from six wells (T813-1H, T814-1H, T820(K), TP37, TP313H and YK17) of Tahe oil field and YAKELA gas field in Tarim Basin were collected and stored in stainless-steel cylinders. These samples were selected to measure concentration and isotope ratio of noble gases, and the results further clarified the regional tectonic activity differences between Tahe oil field and YAKELA gas field, and the differences on source rock characteristics.