深源物质参与湖相烃源岩生烃作用的初步研究*——以准噶尔盆地吉木萨尔凹陷二叠系黑色岩系为例

新疆北部地区二叠系芦草沟组的黑色岩系是重要的生烃岩系。在准噶尔盆地吉木萨尔凹陷,该套岩系主要分布于3000~3500 m,并可分出3100~3170 m和3250~3370 m这2个致密油层段。两层段黑色岩系的岩性以凝灰岩、沉凝灰岩、凝灰质泥晶白云岩为主,夹丰富的纹层状、透镜状沥青质和藻类。黑色岩系中不仅发育火山喷发的深源碳酸质凝灰物质,而且夹有丰富的热液喷流的深源物质,它们多与泥晶微生物白云岩呈互层状,共同组成了具良好生烃能力的特殊烃源岩系。黑色岩系样品的热解分析表明,其中的游离烃S₁含量较高(最高8.17 mg/g,平均1.56 mg/g),裂解烃S₂含量也高(3.3~76.2 mg/g);总有机碳TOC为1.4%~7.9%,生烃潜量PI也为高值(0.02~0.51,平均为0.16),总体指示有机质丰度高、生烃潜能好。生物标志物C₂₈和C₂₉甾烷的含量大于C₂₇,呈反“L”型,表明有机质类型以藻类和高等植物为主;高成熟度甾烷参数C₂₉20S/(20S+20R)和C₂₉ββ/(αα+ββ)在深源物质丰富的致密油层中较高(平均0.48和0.31),而在深源物质少的层位中较低(平均为0.37和0.26)。上述2个层段的地化参数在纵向上的分布特征与镜质组反射率R_O的分布规律(2个致密油层段中深源物质多时R_O呈现异常高值)相吻合。综合分析认为,频繁的火山喷发物质和热液喷流的深源物质参与了该区湖相沉积烃源岩的生烃作用过程。

A preliminary study on the relationship between deep-sourced materials and hydrocarbon generation in lacustrine source rocks: An example from the Permian black rock series in Jimusar sag,Junggar Basin

The black rock series of the Permian Lucaogou Formation are an important hydrocarbon source rocks in northern Xinjiang. In Jimusar Sag,this suite of rock series is mainly distributed at a depth of 3000-3500 m,and it can be divided into two tight oil reservoirs of 3100~3170 m and 3250~3370 m. The lithology of the two black rock series is mainly tuff,tuffite and tuff micritic dolomite,with rich lamellar,lenticular asphaltene and algae. Further study showed that the black rock series not only developed tuff deep source materials,but also contained abundant hydrothermal deep source materials,most of which were interbedded with microbial dolomite and formed a set of special hydrocarbon source rocks with good hydrocarbon generation ability. Pyrolysis analysis of black rock series samples shows that the free hydrocarbon S₁ content is high(the highest is 8.17 mg/g,and 1.56 mg/g on average),and the cracked hydrocarbon S₂ content is also high(3.3~76.2 mg/g). TOC is 1.4%~7.9%,and the potential hydrocarbon generation is also high(0.02~0.51,0.16 on average),indicating high abundance of organic matter and good hydrocarbon generation potential. The content of sterane in biomarkers C₂₈ and C₂₉ is greater than that in C₂₇,showing an inverse “L” type,indicating that algae and higher plants were the main types of organic matter. The maturity parameters C₂₉ 20S/(20S+20R)and C₂₉ ββ/(αα+ββ)are high in the deep source materials rich layers(mean 0.48 and 0.31),and low in the deep source materials few layers(mean 0.37 and 0.26). In the two tight oil reservoirs,R_O value is high when tuff material is abundant. Comprehensive analyses indicate that frequent volcanic eruptions and the deep source materials from hydrothermal are involved in hydrocarbon generation of lacustrine sedimentary source rocks.