煤系氦气富集机理与资源潜力-以鄂尔多斯盆地东缘为例

Accumulation mechanisms and resource potential of helium in coal measures:A case study of the eastern margin of the Ordos Basin

【背景】氦气因其化学性质稳定、导热性能好等优势,被广泛应用于国防、军工、航空、航天等高科技领域,具有不可替代的作用。目前我国氦气主要源于进口,对外依存度高,氦气资源安全问题突出。前人对氦气的研究主要集中在常规天然气,对煤系氦气的关注较少。【目的和方法】为了明确煤系中氦气资源分布及资源潜力,对鄂尔多斯盆地东缘(鄂东缘)煤系气进行取样分析,系统研究氦气分布规律及其控制因素。并结合沁水盆地煤层气中氦气测试结果,对比这两大盆地煤系中氦气富集机理,深入研究煤系中氦气资源潜力。【结果和结论】结果表明:鄂东缘韩城和大宁–吉县深部煤层气中氦气含量高于中浅部煤层气,其中,韩城深部和中浅部煤层中氦气平均体积分数分别为0.0428%和0.0130%,大宁–吉县深部和中浅部煤层中氦气平均体积分数分别为0.0307%和0.0121%;煤系致密气和深部煤层气中氦气含量相当,其中,韩城和大宁–吉县致密气中氦气平均体积分数分别为0.0467%和0.0355%,但都属于贫氦煤层气;三交北区块煤系气中氦气含量较高,平均0.0930%,近一半的井可以达到富氦煤系气标准。鄂东缘煤系中原位自生氦气极少,主要来源于深部基底岩石、铝土岩和紫金山岩体,氦源岩的分布决定了煤系中氦气的分布。鄂东缘断裂系统是深部氦源和紫金山岩体中氦气的有利运移通道,断裂系统的发育强度和位置是氦气运移、聚集的关键,有效的盖层和封闭的水体环境是氦气保存的必要条件。沁水盆地原位自生氦气较少,成藏后期剧烈构造抬升是煤层氦气散失近90%的主要原因。深部煤层气和煤系致密气中氦气浓度相对较低,但是资源量巨大,应加大煤系氦气资源勘查力度。同时,应加强对贫氦–含氦煤系天然气的提氦技术攻关,有效利用煤系天然气中的低浓度氦气,以保障国家的氦气资源安全。

Background Helium,with advantages such as stable chemical properties and high thermal conductivity,has been extensively applied in high-tech sectors like national defense,military,aviation,and aerospace,playing an irreplaceable role.Presently,helium in China is primarily imported from other countries,manifesting a high degree of dependence on foreign trade,suggesting a prominent issue concerning helium resource security.Previous studies on helium principally focus on conventional natural gas,rendering helium in coal measures relatively under-studied.Objective and Methods To determine the distribution and potential of helium resources in coal measures,this study analyzed the coal-measure gas sampled from the eastern margin of the Ordos Basin,systematically investigating the distribution patterns of helium and its controlling factors.In combination with the helium test results of coalbed methane(CBM)in the Qinshui Basin,this study compared the helium accumulation mechanisms of coal measures in the Ordos and Qinshui basins and delved into the helium resource potential in the coal measures.Results and Conclusions The results indicate that deep CBM exhibits higher helium content than moderately shallow CBM in the Hancheng and Daning-Jixian blocks along the eastern margin of the Ordos Basin.Specifically,the helium in deep and moderately shallow coal seams in the Hancheng block exhibits average volumetric fractions of 0.0428%and 0.0130%,respectively;the corresponding values of the Daning-Jixian block are 0.0307%and 0.0121%,respectively.The tight gas in coal measures and the deep CBM manifest similar helium content.The helium in the tight gas of the Hancheng and Daning-Jixian blocks displays average volumetric fractions of 0.0467%and 0.0355%,respectively,suggesting helium-deficient CBM.Contrastingly,the coal-measure gas in the Sanjiaobei block displays relatively high helium content(average volumetric fraction:0.0930%),with nearly half of the gas wells reaching the criterion for helium-rich coal-measure gas.The coal measures along the eastern margin of the Ordos Basin bear minimal content of in-situ authigenic helium,which originates primarily from deep basement rocks,bauxites,and the Zijinshan pluton.The distribution of helium source rocks determines the distribution of helium in the coal measures.The fault system along the eastern margin of the Ordos Basin provides favorable migration pathways for helium in the deep helium sources and the Zijinshan pluton.The development intensity and location of the fault system play a crucial role in helium migration and accumulation.Meanwhile,effective cap rocks and the closed water environments are essential for helium preservation.Besides,the Qinshui Basin shows a relatively low content of in-situ authigenic helium,and the significant tectonic uplift in the late stage of helium accumulation is the primary cause of the loss of nearly 90%helium in coal seams.Despite relatively low helium content,tight gas in the coal measures and the deep CBM demonstrate considerable helium resources,thus warranting more endeavors to helium resource exploration in coal measures.Moreover,it is necessary to put more effort into tackling technological challenges in helium recovery from helium-deficient to helium-bearing coal-measure gas.The purpose is to effectively utilize the low-content helium in coal-measure gas in order to ensure China’s helium resource security.