准噶尔盆地东部古生界深层天然气轻烃地球化学特征

Geochemical characteristics of light hydrocarbons associated with deep natural gas in the Paleozoic of the eastern Junggar Basin

自2020年准噶尔盆地东部(准东)阜康凹陷东斜坡区风险探井——康探1井在二叠系储层连获油气高产以来,中国石油加强了对该区域古生界深层油气的勘探。为进一步探究准东埋深超过4 500 m的深层天然气勘探潜力,对准东地区阜康凹陷、北三台凸起和东道海子凹陷的9个古生界深层天然气样品中的C1—C7系列烃类进行气体和轻烃组分及单体烃稳定碳同位素组成实验分析,研究了其成因类型、成熟度和可能的次生改造作用。结果表明:研究区天然气可分为3类:第一类为二叠系芦草沟组咸水湖相烃源岩生成的油型气;第二类为石炭系煤系烃源岩生成的煤型气;第三类为上述2种来源天然气的混源。研究区天然气整体进入成熟—高成熟阶段,庚烷值和异庚烷值分别为16.74%~32.59%和1.46~2.60,等效镜质体反射率为1.12%~1.57%。研究区天然气未遭受水洗、蒸发分馏和生物降解等次生改造作用,具备较好的天然气保存条件,说明自康探1井重大突破后,该区域古生界深层有望成为准噶尔盆地东部天然气勘探的重要接替区。

Since 2020,when the Kangtan 1 risk well in the east slope area of the Fukang Depression in the east⁃ern part of the Junggar Basin obtained successive high oil and gas production in the Permian reservoir,PetroChi⁃na has strengthened its exploration of deep Paleozoic hydrocarbons in the area,and in order to further explore the potential of deep natural gas exploration in the eastern Junggar Basin with a burial depth of more than 4500 m,the C1-C7 series hydrocarbons in nine Paleozoic deep natural gas samples from the Fukang Depression,the Bei⁃santai Bulge and the Dongdaohaizi Depression in the Junggar Basin were analyzed for gas and light hydrocarbon composition and stable carbon isotope composition of the individual hydrocarbons.The type of genesis,maturi⁃ty,and possible secondary modification were investigated.The results show that the natural gas in the study ar⁃ea can be categorized into three types:the first type is oil-type gas generated from the saline lake-phase hydro⁃carbon source rocks of the Permian Lucaogou Formation;the second type is coal-type gas generated from the Carboniferous coal-phase hydrocarbon source rocks;and the third type is the mixed source of natural gas from the above two sources.The natural gas in the study area is in the mature to high maturity stage,with heptane and isoheptane values of 16.74%-32.59%and 1.46-2.60 respectively,and equivalent vitrinite reflectance of 1.12%-1.57%.The natural gas in the study area has not suffered from secondary modification effects such as water washing,evaporation fractionation,and biodegradation,and has been in a good preservation condition,indicating that since the significant breakthrough of Well Kangtan 1,the deeper layers of the Paleozoic in this ar⁃ea are expected to become an important successor area for natural gas exploration in the eastern Junggar Basin.