济阳拗陷非烃类气藏(CO_2、He)的成因探讨

GENESIS OF THE NON HYDROCARBON GAS RESERVOIR(CO 2、He) IN JIYANG DEPRESSION

济阳坳陷是在古生代克拉通背景上形成的陆内拉张盆地；坳陷内的非烃类气藏分布于高青—平南深断裂中南段和阳信次级凹陷西北缘及商店火山岩穹隆构造内。ＣＯ２含量为６８．８５～９８．５９％，Ｈｅ含量为（８４～８４７）×１０－６，ＣＯ２与Ｈｅ呈弱的正相关。ＣＯ２的δ１３Ｃ值为－６．３０‰～－３．３５‰，表明ＣＯ２为无机成因。３Ｈｅ／Ｈｅ的比值为（２．８０～５．２２）×１０－６，表明Ｈｅ来源于地壳和地幔。研究表明非烃类气藏中的ＣＯ２主要为来自地球深部的幔源ＣＯ２。

Jiyang depression is a land pull apart basin.It underwent Europe Asia plate、Kula Pacific plate and Indian Plate cross acted based on Palaeozoic Era craton from Trisaaic period.The non hydrocarbon gas pool and mainly distributes in the middle south of Gaoqin Pingnan deep fault and the West North of Yangxin secondary depression and the Shang Dian igneous rock dome structrue in Jiyang depression.CO 2 content is 68.85～98.58%and He content is (84～847)×10 6 ;all component content has great variation.CO 2 content has negative correlation with CH 4 content,and weak positive correlation with He content.The δ 13 C values of CO 2 are 6.30‰～ 3.35‰ in Jiyang depression non hydrocarbon gas pool.It is consistent with δ 13 C principal frequency of abiogenic CO 2 ( 6‰- 3‰)in our country, showing that the CO 2 in the gas pool is inorganic.The δ 13 C principal frequency of CO 2 is 4.76‰～ 4.32‰.The consistence with the δ 13 C values of mantle derived and magmatic CO 2 , shows that the CO 2 originated fron the earth deep.The 3He/ 4He values are (2.80～5.22)×10 6 ,i.e.,R/Ra are 2.00 3.73.It shows that He in the gas pool is the mixture of crust derived He and mantle derived He.The mantle derived He is 19.89%￣37.34% in the total He.The principal frequencies of 3He/ 4He values are (3.55～4.49)×10 6 ,i.e.,R/Ra are 2.54～3.18.It is close to the 3He/ 4He member values of magma.It shows the He in the gas pool comes from the earth deep.The gas bearing reservoirs of different depth have different 3He/ 4He values in the same natural gas well.The 3He/ 4He values in the deep are much more than those in the lower,e.g.Hua 17 well;it shows that He comes fron the earth deep ,reflecting the characters of mantle outgassing .The 40 Ar/ 36 Ar values are 317 1791.The principal frequencies are 770￣1791.The gas bearing reservoirs of different depth have different 40 Ar/ 36 Ar value in the deep is much more than that in the lower,e.g.Hua 17well;it shows that Ar comes from the earth deep,reflecting the characters of mantle outgassing.