【作者】 张文；

【导师】 赵峰华；

【作者基本信息】 中国矿业大学(北京) ， 矿产普查与勘探， 2019， 博士

【摘要】 氦气是一种战略性资源,因其化学惰性、低沸点、低密度的特性,不仅广泛应用在低温超导、工业生产和科学研究等领域,而且在核工业和航天方面有不可替代的应用。我国是贫氦国家,氦气主要依赖进口,受制于人,氦气资源安全形势严峻。本论文综合运用稀有气体地球化学、油气地球化学、油气地质学和矿物学等学科知识,使用稀有气体同位素质谱仪、激光荧光仪、紫外可见分光光度计、电感耦合等离子体发射光谱仪、电感耦合等离子体质谱仪和电子探针,以关中盆地地热田和柴北缘油气田为研究区,在明确研究区氦气富集情况和成因类型的基础上,分别从氦气的生成、释放和运聚三个方面系统研究了氦气成藏机理,总结出氦气成藏模式和富集条件。分析井口气氦气含量及同位素,明确研究区氦气富集情况和成因类型。关中盆地本次采集的地热伴生气中He含量为0.05-2.94%,高于其工业标准0.05-0.1%。柴北缘地区马北气田He含量(0.06-0.20%)高于工业标准,牛东气田(0.01-0.02%)低于标准,东坪气田氦含量变化较大(0.02-0.48%),部分区域达到标准。两个区域He同位素值均显示壳源氦气特征。调研世界富氦气藏的地质背景,揭示壳源氦气藏与花岗岩的关系,讨论花岗岩中氦气生成特征。关中盆地南缘露头花岗岩和银额盆地井下花岗岩均富铀钍,铀钍平均含量高于克拉克值,但各岩体中铀钍非均质性强,电子探针显示以铀钍独立矿物和铀钍类质同象矿物两种形态赋存。花岗岩可生成大量氦气,与关中盆地有关的花岗岩氦气生成量为142.76亿方,远高于根据地热流体估算的盆地内氦气资源量(21.30 亿方)。研究花岗岩中氦气释放机理,总结出花岗岩中氦气释放模式。采用真空破碎、加热熔融和分段加热三种方法提取稀有气体,结果表明:①花岗岩中仅部分氦气可保存在岩石中(1.5-17.4%),结合前人研究,认为花岗岩中氦气的释放比率高达80%。氩气相对于氦气更难从岩石中释放出去。②温度是影响花岗岩中氦气释放的首要因素。250℃下,花岗岩对4He无封闭能力,丢失90%4He仅需6.4天。铌钛铀矿中4He封闭温度为125℃,该温度下丢失90%的4He需要2.5百万年。结合其他副矿物的封闭温度,认为27-250℃(400-7800m)为He部分封存区,低于27℃(400m以浅)为He完全封闭区,高于250℃(>7800m)为He不封存区。③断裂可进一步将不受温度封存的He运移至地壳浅部的流体系统中成藏。分析关中盆地稀有气体分馏过程,建立地热田地下水运移和氦气运聚成藏模式。空气来源的稀有气体(ADGs,e.g.,20Ne,36Ar,84Kr,130Xe)模拟结果表明,该地区经历过开放系统中重油-水瑞利分馏,且Kr和Xe富集°华县2井附近存在游离气藏,4He通量高。关中盆地氦气成藏模式如下:①地下水补给,ADGs随之运移至地下;②壳源气体(4He,40Ar*等)从地壳岩石中释放出来并溶解到地下水中,该过程持续0.30-1.98Ma。③地下水经历油-水分馏阶段;④主要气体组分(N2和CH4)生成并加入到地下流体系统中。随着甲烷补给量的增大,依次形成高氦弱气水溶气藏、低氦强气水溶气藏和高氦游离气藏。讨论柴北缘地区稀有气体分馏模型,建立油气田油气充注和氦气运聚成藏模式。柴北缘地区经历了油水-气水的多阶段相分馏过程,马北地区多油少气,东坪地区变化大,总体少油多气,牛东地区的油气特征介于马北和东坪之间。根据分馏模型,明确了氦气随地下水进行运移,计算了分馏前地下水中的4He含量,建立了柴达木盆地的氦气成藏模式:①地下水补给;②氦气初次运移。地壳岩石中衰变产生氦气释放并保存在(微)孔隙或(微)裂隙中的地下水中,在马北、东坪和牛东分别持续1.84-2.78,1.07-2.11和0.31-0.49Ma。③氦气二次运移。当油气集中生成而大规模运移时,地下水先后与油相和气相接触,导致溶解度极低的氦气从地下水中脱溶进入气相,随烃类一起运移至气藏。④油气藏形成后氦气补给可忽略不计。提出氦气富集的三大有利条件:①富铀钍的花岗岩区及古老地台的新构造活动区可为氦气藏提供丰富的来源;②地下流体系统中存在游离天然气藏,气-水平衡使溶解度极低的氦气,不断脱溶进入气藏,而非随地下水运移而散失,因此水溶气脱溶形成的气藏极有可能富集氦气;③气藏中主要组分的补给量适中,减小对前期形成的高氦气相的稀释作用,所以“低品位”气藏更容易发现较高氦气含量,对该类气田可进行天然气和氦气的综合利用。更多还原

【Abstract】 Helium,a strategic resource,is not only widely used in low temperature superconducting,industrial production and scientific research,but also has irreplaceable applications in nuclear industry and aerospace due to its chemical inertness,extremely low boiling point and low density.China has little domestic helium and depends on imports,making the security of helium resource grim.This study takes the Guanzhong geothermal field and the North Qaidam oil and gas field as research areas,uses the knowledge of rare gas geochemistry,oil and gas geochemistry,oil and gas geology and mineralogy and adopts the methods of rare gas isotope mass spectrometer,laser fluorometer,ultraviolet visible spectrophotometer,ICP-OES(inductively coupled plasma optical emission spectrometer),ICP-MS(inductively coupled plasma mass spectrometer)and EPMA(electron probe micro-analyzer).The enrichment and genetic types of helium in Guanzhong and North Qaidam Basin were studied.The accumulation mechanism of helium xvas discussed systematically from the three aspects of helium production,release and migration.The accumulation model and favorable enrichment conditions of helium were summarized.This research analysed the helium content and isotopic ratios of wellhead gas samples and determined tlie enrichment and genetic types of helium in the study area.The helium contents in associated gas collected from geothermal wells in Guanzhong Basin are 0.05-2.94%,which are higher than the helium industrial standard of 0.05-0.1%.In the North Qaidam area,the helium contents in the Mabei gas field(0.06-0.20%)are higher than the industrial standard,those in the Niudong gas field(0.01-0.02%)are lower than the standard,and those in Dongping gas field varies greatly(0.02-0.48%)and part of them reach tlie standard.The helium isotopic values suggest that helium in the two regions is both derived from the crust.On the base of the investigation of the geological settings of the global helium-rich gas reservoirs,the relationship between the crust-derived helium reservoirs and the granite bodies were revealed.Therefore,this study discussed the characteristics of helium generation in granite.The outcropped granite in the southern margin of the Guanzhong Basin and the underground granite in the Yin’e Basin are rich in uranium and thorium.The average contents of uranium and thorium are higher than the Clark values,but they are highly heterogeneous in granite.The electron probe shows that there are two occurrence states for U and Th in granite:U-Th independent minerals and U-Th isomorphic minerals.Granite can generate a large amount of helium.The amount of helium generated from granites related to the Guanzhong Basin is 14.276 billion square meters,which is much higher than the amount of helium gas estimated from the geothermal fluids in the basin(2.130 billion square meters).The release mechanism of helium in granite was studied and the release mode of helium in granite was summarized.Three kinds of gas release methods,namely vacuum crushing,melting and step-wise heating,were used to release noble gases in our studies,the results are as follows:1)Only a portion of the helium in the granite can be closed in the rock(1.5-17.4%).Combined with previous studies,the release ratio of helium in granite is as high as 80%.Argon is more difficult to release out of rocks than helium.2)Temperature is the primary factor controlling the release of helium in granite.At 250℃,granite has no retention ability for 4He and the loss of 90%of 4He takes only 6.4 days.The 4He closure temperature of betafite is 125℃.At this temperature,it takes 2.5 million years to lose 90%of the 4He.Combined with the 4He closure temperature of other secondary minerals,it is concluded that 27-250℃(400-7800m),below 27℃(shallow than 400m)and above 250℃(deeper than 7800m)are the He complete,partial and none retention zone respectively.3)The fracture can further migrate the free He,which is not closed in minerals by temperature,into the fluid system of the shallow strata.The noble gas fractionation process in the Guanzhong Basin was discussed and the groundwater evolution and helium migration and accumulation mode in the geothermal field was established.The modelling results of air-derived noble gases(ADGs,e.g.,20Ne,36Ar,84Kr,130Xe)indicate that the heavy oil-water Rayleigh fractionation in open systems occurred in this region.There is a free gas reservoir near the Huaxian 2 well,where the 4He flux is high.The helium accumulation mode in the Guanzhong Basin is as follows.1)Groundwater were recharged and the dissolved ADGs were transported to the underground.2)Crust-derived gases(4He,40Ar*,etc.)were released from the crustal rocks and dissolved into the groundwater and the process lasts 0.30-1.98 Ma.3)After the hydrocarbon generation,groundwater underwent oil-water equilibrium.4)Major gas components(N2 and CH4)entered into the underground fluid system.With the increase of methane supplementary amount,there different helium reservoirs were formed in the Guanzhong Basin,namely,high helium-weak gas dissolved gas reservoirs,low helium-strong gas dissolved gas reservoirs,high helium free gas reservoir.The noble gas fractionation model in the North Qaidam Basin was discussed and the hydrocarbon charging and helium migration and accumulation model in oil and gas field was established.The North Qaidam area experienced a multi-stage phase fractionation process of oil-water and gas-water equilibrium.The Mabei area has the highest amount of oil and the Dongping area has the highest quantity of gas generally.The oil and gas characteristics of Niudong area are between Mabei and Dongping.According to the results of the fractionation model,the 4He content in the groundwater before oil-gas-Water fractionation was calculated,and the helium accumulation model in the Qaidam Basin was established.1)Groundwater recharge.2)Primary migration of helium.Helium generated by radiogenic decay of U and Th in the crust released and migrated into groundwater preserved in(micro)pores or(micro)fractures,which lasts 1.84-2.78,1.07-2.11 and 0.31-0.49Ma in Mabei,Dongping and Niudong respectively.3)Secondary migration of helium.When oil and gas are generated and migrated in a large scale,the groundwater would be in contact with the oil phase and the gas phase,resulting in the exsolution of helium,which has an extremely low solubility in water,out of groundwater.Helium would migrate along with the hydrocarbons and move into the gas reservoir.4)After the formation of oil and gas reservoirs,the supply of helium is negligible.Three favourable conditions for helium enrichment are proposed.1)The uranium-rich granitoid body and the neotectonic activity zone of the ancient platform can provide a rich source for helium.2)Free gas phase exists in the underground fluid system.Gas-water equilibrium makes helium gas continuously degassed into gas phase rather than migrate elsewhere,so the gas reservoir formed by the exsolution of water-soluble gas is very likely to be enriched in helium.3)The supplement of the major gas components in the gas reservoir is moderate.Otherwise,the gas formed in the later sage would dilute the gas with high helium content formed in the earlier stage.Therefore,it is more prone to find high helium content in a "low grade" gas reservoir,and comprehensive utilization of natural gas and helium gas can be carried out for this type of gas field.更多还原