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壳源氦来自地质体中铀钍等氦源元素的放射性衰变,其生成速度极其缓慢,不存在集中的生气高峰,相对常规油气为典型的弱源气。其常以甲烷或二氧化碳气藏的伴生气产出,因稀有性而低丰度(0.1vol%)即可成矿,且成藏与地下水关系密切。为研究其弱源成藏机理,总结了前人关于氦气、氮气和甲烷亨利系数和溶解度的研究成果,以渭河盆地为例,通过模拟计算探讨了亨利定律在氦气运移和成藏中的关键作用。根据亨利定律,稀溶液中气体溶解度受控于气体的分压和亨利系数。与载体气相比,氦气的亨利系数高,且高低温下相差较大,特别是在氦源岩和气藏中的分压差别显著,造成两处的溶解度差异显著,使以溶解态运移的弱源氦气能够脱溶成藏。综合分析认为:①氦气在深部氦源岩处分压大、温度高,能溶解于水而运出;②运移至浅部遇到天然气等载体气藏时,在气水界面,氦气分压极低而脱溶进入气藏,载体气则溶解进入水中,好似载体气将氦气从水中“置换”出来。这种作用使气藏附近形成溶解氦低浓度漏斗,水溶氦不断向气藏附近迁移而进入气藏,大大提高了氦气运聚系数;③氦气进入气藏后,由于盖层中氦气分压低而难溶于水,不易扩散,利于保存。研究结果明确了氦气在氦源岩“运得出”、遇气藏“脱得出”、进气藏“保得住”的高运聚系数富集机制,为氦气资源勘查提供了理论依据。
Shell-derived helium comes from radioactive decay of helium source elements such as uranium and thorium in geological bodies. Its generation rate is extremely slow, and there is no concentrated peak of gas concentration, which is typical of weak source gas. It is often associated with methane or carbon dioxide gas reservoir gas production due to its low abundance (0.1vol%) can be mineralized, and the accumulation of water and groundwater are closely related. In order to study the mechanism of weak source accumulation, the previous research results about the Henry coefficient and solubility of helium, nitrogen and methane were summarized. Taking Weihe basin as an example, the Henry’s law was discussed through the simulation calculation. The key role. According to Henry’s Law, the gas solubility in dilute solutions is governed by the partial pressure of gas and the Henry factor. Compared with the carrier gas, the helium has a high Henry’s coefficient and a large difference between high and low temperatures, especially in the partial pressures of helium source rocks and gas reservoirs, resulting in significant differences in solubility between the two, Weak source of helium can dissolve into reservoir. The comprehensive analysis shows that: (1) Helium gas has a high partial pressure of helium source rock at high temperature and can be dissolved in water and transported out; (2) when transported to a shallower gas carrier such as natural gas, Pressurized and desolventized into the gas reservoir, the carrier gas is dissolved into the water, as if the carrier gas expelled helium from the water. This action makes the formation of a low-concentration funnel with dissolved helium near the gas reservoir. The water-soluble helium continuously migrates into the gas reservoir near the gas reservoir and greatly increases the entrained coefficient of helium. ③ When helium enters the gas reservoir, Partial pressure is low and insoluble in water, not easy to spread, which will help save. The results of this study clearly indicate that the enrichment mechanism of helium in the high-temperature co-ordination coefficient of helium source rock, “transported out”, met the gas reservoir “get out ”, intake reservoir Exploration provides a theoretical basis.