亨利定律与壳源氦气弱源成藏——以渭河盆地为例  

Henry's Law and accumulation of crust-derived helium:A case from Weihe Basin,China

作　　者：李玉宏[1,2] 张文[2] 王利[3] 赵峰华[2] 韩伟[1] 陈高潮[1] Li Yu-hong Zhang Wen Wang Lia Zhao Feng-hua Han Wei Chen Gao-chao(Xi ＇an Center ,China Geological Survey ,Xi ＇an 710054 ,China College of Geoscience and Surveying Engineering ,China University of Mining and Technology ,Beijing 100083 ,China Resources Evaluation Department ,China Geological Survey ,Beijing 100037 ,China)

机构地区：[1]中国地质调查局西安地质调查中心,陕西西安710054 [2]中国矿业大学(北京)地球科学与测绘工程学院,北京100083 [3]中国地质调查局资源评价部,北京100037

出　　处：《天然气地球科学》2017年第4期495-501,共7页Natural Gas Geoscience

基　　金：国家自然科学基金面上项目(编号:41572131);中国地质调查局矿产资源调查评价项目(编号:121201011000150014)联合资助

摘　　要：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。Crust-derived helium is generated from the radioactive decay of uranium,thorium and other helium-derived elements in geological bodies.Compared with conventional natural gas,helium is a typical weak source gas as a result of extremely slow generation rate and absence of generation peak.It is associated with methane or carbon dioxide reservoirs frequently and related to groundwater closely.Helium can reach the industry standard with 0.1% in volume fraction.In order to study the accumulation mechanism of helium,the previous results on Henry’s coefficient and solubility of helium,nitrogen and methane are summarized and the key roles of Henry’s Law in the helium migration,accumulation and preservation are discussed by simulating calculation in Weihe Basin.According to the Law,the gas solubility in dilute solution is controlled by the gas partial pressure and Henry coefficient.Compared with the carrier gases,the Henry constant of helium is high,with striking difference in low and high temperature and the helium partial pressure is greatly different in helium source rocks and gas reservoirs,resulting in the great differences of helium solubility in the two places.The accumulation progresses are as follows.Firstly,helium can dissolve into water and migrate out of helium source rocks due to the high partial pressure and high temperature,causing high solubility.Secondly,when water soluble helium is transported to the shallow gas reservoir,it is prone to be out of solution and into reservoir due to the extremely low partial pressure and low temperature.Meanwhile part of carrier gas dissolves into water,as if the helium is “replaced” out.Furthermore,the low concentration funnel of dissolved helium is formed near the gas reservoir and other dissolved helium continues to migrate towards the gas reservoir,which greatly improves the helium accumulation coefficient.Finally,when entering the gas reservoir,helium is difficult to dissolve into water of cap layers due to the low partial pressure,resulting in the preservation

关 键 词：氦气 成藏 亨利定律 渭河盆地 

分 类 号：TE132[石油与天然气工程—油气勘探]