【摘要】 准噶尔盆地玛湖凹陷是区内重要的富烃凹陷,其二叠系风城组作为主力烃源岩层系,被广泛认为是页岩油勘探的关键“甜点”目标。相较于研究程度较高的玛湖凹陷中心及其北部斜坡区,西南部斜坡区(玛南)地区处于湖盆边缘相带,其烃源岩品质、有机质赋存状态及古环境演化特征具有特殊性,但目前相关成因机理认识尚不清晰。基于此,以玛南地区12口井33个泥页岩样品为研究对象,综合利用有机岩石学、有机地球化学与碳同位素分析等方法开展了系统测试,包括总有机碳(TOC)含量与总硫(TS)含量测定、岩石热解实验、镜质体反射率(R_o)测定、氯仿沥青“A”抽提、饱和烃与芳香烃气相色谱-质谱(GC-MS)分析以及全岩抽提物与族组分碳同位素组成测定,系统评价了其地球化学特征与成烃潜力。研究结果发现,玛南地区风城组烃源岩有机质丰度总体达到好—极好级别,但受陆源碎屑稀释及搬运影响,有机质类型以Ⅱ—Ⅲ型混合为主,与玛湖凹陷北部地区典型的Ⅰ—Ⅱ型有机质存在显著差异;样品整体处于成熟生油高峰阶段(R_o>0.8%),在详细探讨并剔除高成熟度对生烃母质参数(如姥植比、β-胡萝卜烷、扩展三环萜烷比值等)改造作用的基础上,多指标综合判识证实有机质主要来源于藻类、细菌等低等水生生物,陆源高等植物输入较为有限;沉积环境方面,该区主要形成于咸化湖盆边缘斜坡环境,受内源化学沉淀与外源陆源碎屑注入的双重控制,水体呈现弱还原、高盐度特征。研究明确了玛南地区风城组烃源岩作为湖盆边缘相咸化混积岩页岩油富集区的物质基础,揭示了其与凹陷中心及北部沉积环境的差异性,为拓展准噶尔盆地页岩油勘探空间提供了理论依据。更多还原

【Abstract】 [Objective] The Mahu Sag,a pivotal,hydrocarbon-rich depression within the Junggar Basin,hosts the Permian Fengcheng Formation,a primary source rock interval widely regarded as a key " sweet spot" target for shale oil exploration.Unlike the well-studied depocenter and northern slope of the Mahu Sag,the Southern Mahu Sag represents a marginal lacustrine facies.Although possessing distinct source rock quality,organic matter(OM) occurrence,and paleoenvironmental evolution,the underlying genetic mechanisms remain poorly constrained.[Methods] To address this,this study integrates organic petrology,molecular geochemistry,and stable carbon isotope analyses on 33 mudstone and shale samples from 12 wells in the Southern Mahu Sag.Systematic tests were conducted to comprehensively evaluate the geochemical characteristics and hydrocarbon generation potential.These included determination of the total organic carbon(TOC) and total sulfur(TS) content,Rock-Eval pyrolysis,measurement of vitrinite reflectance(R_o),chloroform bitumen "A" extraction,gas chromatography-mass spectrometry(GC-MS) of saturated and aromatic hydrocarbons,and analysis of the carbon isotope compositions of extracts and fractions.[Results] The results indicate that the OM abundance of the Fengcheng Formation source rocks in the Southern Mahu area generally reaches good to "excellent" levels.However,affected by the dilution of terrigenous detritus and transport effects,the OM is predominantly mixed Type Ⅱ-Ⅲ kerogen,contrasting significantly with the Type Ⅰ-Ⅱ OM typically found in the Northern Mahu area.The samples are generally within the peak oil-generation window(R_o>0.8%).[Conclusions] After rigorously assessing and calibrating the thermal maturity effects on source-related parameters(e.g.,Pr/Ph,β-carotane,and ETR),multi-proxy analysis confirms that the OM mainly originates from lower aquatic organisms,such as algae and bacteria,with limited input from higher terrestrial plants.Regarding the depositional environment,the study area primarily evolved in a saline lacustrine slope setting,characterized by dual control of endogenous chemical precipitation and exogenous terrigenous detrital input.The water column exhibited weak reducing and high-salinity conditions.[Significance] This study(i) elucidates the material basis of the Fengcheng Formation source rocks as a "saline mixed sedimentary" shale oil enrichment zone in a marginal facies,(ii)reveals the depositional heterogeneity compared to the sag center and northern slope,and(iii) provides a theoretical foundation for expanding shale oil exploration in the Junggar Basin.更多还原