内蒙古西乌旗地区MXD-1井下二叠统寿山沟组细碎屑岩有机地球化学特征

Organic geochemistry of fine-grained clastic sedimentary rocks of the Lower Permian Shoushangou Formation from MXD-1 Well,in Xi Ujimqin Banner,Inner Mongolia

下二叠统寿山沟组被视为二连盆地及其外围古生界重要的生烃层位,但是针对该套地层的有机地球化学研究程度较低,前期采集的样品多出露地表受风化作用影响严重,井下岩芯样品的有机地球化学研究还鲜有报道。本文以西乌旗地区MXD-1井下二叠统寿山沟组岩芯样品为主要研究对象,通过分析有机质丰度、有机质成熟度、有机质类型并结合有机分子地球化学特征,深入探讨了寿山沟组细碎屑岩油气资源潜力和古环境意义。研究结果表明:(1)MXD-1井寿山沟组细碎屑岩总有机碳含量(TOC)介于0.26%~0.63%之间,平均值为0.41%;生烃潜量(S1+S2)介于0~0.81‰之间,平均值为0.04‰;镜质体反射率(Ro)介于3.85%~4.36%之间,平均值为4.10%;腐泥组、壳质组、镜质组和惰质组的相对含量分别为66%、18%、16%;(2)m/z 217质量色谱图上规则甾烷相对峰高呈"L"型,甾烷C27—C28—C29判别图中C27甾烷具有明显优势;(3)Pr/Ph值分布在0.49~1.23之间,平均值为0.61;伽马蜡烷指数为0.11~1.22,平均值为0.37;C23-三环萜烷的相对含量为0.24~1.40,平均值为0.73。结合已有的区域地质调查成果分析后认为:研究区寿山沟组细碎屑岩主体沉积于半深海环境,水体盐度较高、还原性强;有机物源具有陆生和水生双重补给,有机质主体属于Ⅱ1型;所分析的样品有机质丰度较低、成熟度较高,但是从沉积环境和有机质类型的角度判识,西乌旗地区寿山沟组细碎屑岩在油气勘查工作中是不容忽视的烃源岩,下一步研究工作需重点关注优质烃源岩的形成机理和有利分布区。

The Shoushangou Formation of Lower Permian is regarded as an important hydrocarbon generation Formation in Erlian(Erenhot)Basin and its peripheral Paleozoic.However,the organic geochemistry of the Formation is relatively low.Most of the samples have been exposed,and the surface weathering has a serious impact on it.In this paper,the core samples of Shoushangou Formation from MXD-1 Well were taken as the main research objects.By analyzing the organic matter abundance,maturity of organic matter,type of organic and combining with the characteristics of molecular organic geochemistry,the oil and gas resource potential and paleoenvironment significance of Shoushangou Formation were deeply discussed.The results showed that:(1)The organic carbon content of fine clastic rocks in Shoushangou Formation from MXD-1 Well was between 0.26%and 0.63%,with an average value of 0.41%;Hydrocarbon potential(S1+S2)was between 0 and 0.8‰,with an average value of 0.04‰;Vitrinite reflectance(Ro)ranged from 3.85%to 4.36%,with an average value of 4.10%;The relative contents of sapropelinite,exinite,vitrinite and inertinite were 66%,18%and 16%,respectively;(2)The relative peak height of sterane mass chromatogram(m/z 217)is"L"type,and C27sterane in C27—C28—C29discrimination diagram has obvious advantages;(3)Pr/Ph ranged from 0.49 to 1.23,with an average value of 0.61;Gammacerane index was 0.11~1.22,with an average value of 0.37;The relative content of C23-tricyclic terpenes ranged from 0.24 to 1.40,with an average value of 0.73;Based on the analysis of the existing regional geological survey results,it is concluded that:Shoushangou Formation is deposited in the bathyal environment,with high salinity and stong reductionability.Source of oaganic matter has a dual supply of terrestrial and aquatic,organic matter subject belongs toⅡ1;The analyzed samples have lower abundance of organic matter and higher maturity,but from the perspective of sedimentary environment and organic matter type,the fine clastic rocks of Shoushangou Formation in Xiujimqin area are the source rocks that can not be ignored in oil and gas exploration and the next research work should focus on the formation mechanism and favorable distribution area of high-quality source rocks.