The calculation of hydrocarbon-generating temperature — Theory and practice

How to quantitatively evaluate the maturity of crude oils is still an open question. Mango discovered a remarkable compositional invariance of four isoheptane ratios in crude oils, and proposed a steady-state catalytic model for the origin of light hydrocarbons. According to this model, 2,4/2,3 dimethylpentane ratio is a pure temperature parameter. Bement, Mango et al. established the functional equation between the two parameters--light hydrocarbon temperature and burial temperature and applied it to the calculation of hydrocarbon-generating temperature, which provided a new choice for the study of oil maturity. In this paper, the Mango＇s parameters for hydrocarbons from the Tazhong area were calculated, the average K1 value is 1.06, which is in good consistency with the Mango＇s proposal that the K1 value is relatively stable. Calculated with the functional formula of hydrocarbon-generating temperature, the hydrocarbon-generating temperatures are with the range of 120-129℃, and the converted vitrinite reflectance （Ro） varies from 0.88% to 0.90%. This is well consistent with the maturity characteristics of neohopanes. The results have verified the reliability of this method.     

甲基二苯并噻吩分布指数（MDBI）作为烃源岩成熟度标尺的探讨

选择库车坳陷和雅布赖盆地两个烃源岩热演化系列,在GC/MS分析的基础上探讨了二苯并噻吩类成熟度参数,如MDR4、MDR23、MDR、MDR’等的热演化特征,首次提出利用甲基二苯并噻吩分布指数(MDBI)作为研究区有效的新型成熟度标尺。结果表明,在成熟至高成熟阶段MDR4和MDR23主要受热力作用控制,在研究区应用效果良好;MDR在较高热演化阶段变化速率显著增加,而且适合于Ⅱ2和Ⅲ型有机质。甲基二苯并噻吩分布指数与其他有效参数,如Ro、tmax和MPI等之间的相关系数矩阵进一步证实,在Ro=0.67%～1.22%范围内,MDBI能够准确提供烃源岩热演化历史方面的信息。该指数的提出还有望为原油热成熟度的判识提供一个新的途径。     

从塔里木盆地看中国海相生油问题

塔里木盆地厚达 5～ 7km的海相寒武、奥陶系 ,可划分出下、中寒武统和中、上奥陶统两套工业性烃源岩。油源对比证实 :盆地目前保存下来的海相成因工业性油藏 ,主要来源于中上奥陶统泥灰岩。正是因为塔里木盆地比四川、鄂尔多斯盆地多了一套中等成熟的中上奥陶统油源岩 ,所以能够找到海相油田。笔者认为 :海相工业性烃源岩不必很厚 ,但w (TOC)应≥0 .5% ,碳酸盐岩要含泥质 ;海相源岩往往并不发育在凹陷中心 ,而发育在 4种有利沉积相带上 ;碳酸盐岩具有“双重母质”的特点 ,浮游藻类偏油 ,底栖藻类偏气。海相源岩的形成模式有“保存模式”和“生产力模式”两种 ,分别对应于塔里木寒武系和中上奥陶统烃源岩。塔里木古生代克拉通早期活动、晚期稳定、持续降温的演化史 ,有利于海相油气的多期成藏和晚期保存。     

江汉盆地西南缘原油中含硫化合物的分布特征及其地球化学意义

对江汉盆地西南缘12个原油样品中含硫化合物分布特征的研究表明,原油中二苯并噻吩系列化合物和苯并萘并噻吩系列化合物分别占芳烃总量的4.61%～9.79%和0.27%～1.32%,与烃源岩中含硫化合物的含量一致,反映原油中含硫化合物的含量与沉积环境有关.原油含硫化合物的内组成表明,咸水环境有利于二甲基二苯并噻吩和三甲基二苯并噻吩系列化合物的相对富集.4-甲基二苯并噻吩/1-甲基二苯并噻吩峰面积比值(MDR)在低成熟阶段(Ro＜0.7%)的变化范围较小,当成熟度进一步增加时,因热稳定性较差的1-甲基二苯并噻吩向其他化合物转化的速度加快,相对丰度降低,而4-甲基二苯并噻吩的相对丰度增加,致使MDR值随成熟度的增加而很快增大.同时,DR值受到沉积条件的影响,可能指示沉积环境的咸水化程度.2 3-甲基二苯并噻吩/二苯并噻吩峰面积比值与4-甲基二苯并噻吩/二苯并噻吩峰面积比值之间表现为正相关,说明2 3-甲基二苯并噻吩与4-甲基二苯并噻吩的形成机理相似,同样受沉积环境和成熟度的影响.     

德南洼陷下第三系低熟油灶的油气运移分配

德南洼陷沙三段（Es3)油灶的低熟度大大降低了德南洼陷的勘探成功率，泥岩压实曲线推测和油气显示资料表明，Es3低熟油灶的油气初次运移主要指向沙四段（Es4)储层，射线追踪法和探井油气显示资料表明德南洼陷油气再次运移分配主要受运移路线，距油灶的远近等因素影响，运移优选通道是近油灶的灰岩裂缝，综合研究认为该区的有利勘探层位是Es4，有利圈闭位于近油灶的两个Ⅰ类油气运移分配单元内，以灰岩中的砂层夹层为主要目标。     

东营凹陷原油、储层吸附烃全扫描荧光特征与应用

应用全扫描荧光分析(TSF、QGF-E)技术对东营凹陷沙河街组40个原油、15个储层包裹烃、39个储层砂吸附烃的三维荧光特征进行了定性与定量分析。分析表明,原油与包裹烃的TSF指纹特征总体相似,均为单峰型,指示油气成因具有内在的联系。观察到不同原油TSF强度峰宽与最高值有异,低成熟度样品往往具有较高的TSF强度及较宽的峰。进一步分析表明,原油TSF最高强度、TSF定量参数R1[270nm(Em360nm/Em320nm)]、R2[260nm(Em360nm/Em320nm)]与生物标志物成熟度参数C29甾烷ααα20S/(S+R)、Ts/(Tm+Ts)等有较好的线性正相关性,反映TSF荧光指纹特征及其定量参数可作为一种温标用于热成熟度分析。应用TSF技术确认东营凹陷中央隆起带原油成熟度具有自西南向东北逐渐降低的变化规律,其反映了油源与油气充注方面的重要信息。对东营凹陷牛庄洼陷两口井的储层砂的QGF-E分析表明,颗粒样品所在层段的烃类含量普遍较高,反映致密薄层砂、微裂缝等可能为该洼陷岩性油气藏重要的隐蔽型油气运移通道。TSF、QGF-E技术在油气族群、储层含油气性、油气运移路径与油层识别等方面具有广泛的应用前景。     

羌塘盆地马牙山沥青脉地球化学特征及其指示意义

本文以沥青抽提物的饱和烃色谱—质谱分析为基础,结合野外露头剖面沉积相分析,剖析了羌塘盆地马牙山沥青的地球化学特征,探讨了其沉积环境、成熟度和油源。测试结果表明：马牙山沥青的正构烷烃不具备明显的奇偶优势,(nC21+nC22)/(nC28+nC29)值较高,Pr/Ph、Pr/nC17值明显较低,C27、C28、C29规则甾烷呈不对称“V”字形分布,4—甲基甾烷普遍存在,Ts/Tm、C29ββ/(αα+ββ)、C2920S/(S+R)等热成熟度构型转化参数比值较低。饱和烃色谱质谱特征表明,沥青母源岩以海相水生生物输入为主,有机质处于低成熟演化阶段,有机母质形成于一定盐度的还原环境。油源对比显示,中侏罗统夏里组烃源岩与马牙山沥青的正构烷烃、甾烷、萜烷等生物标志化合物分布特征具有很好的对比性,反应了二者具有较强的亲缘关系。     

Geochemical Characterizations of Source and Depositional Environment of Hydrocarbons in the Lake Albert Rift Basin

Despite the upsurge in hydrocarbon exploration in the Lake Albert Rift Basin(LARB)over the past three decades,systematic characterization of hydrocarbon compositions remains lacking,leading to uncertainties in source rock and oil generation determination.We characterized crude oil compositions and oil sand samples in the northern and southern subbasins of LARB.The relative abundance of normal and branched linear alkanes,hopanes,steranes,and aromatic hydrocarbon suggest that northern and southern hydrocarbons were deposited in anoxic to suboxic lacustrine environments and share similar biological source compositions(i.e.,a mixture of plants and aquatic algae and bacteria).Relative to southern samples,northern samples show more negative δ¹³C values for oils,saturates and aromatics,indicating longer migration paths,and exhibit higher MPI-1,DNR-1 and 4-/1-MDBT ratios,indicating higher maturity.Between the two possible sets of source rocks(upper Miocene and Jurassic strata),the positive δ¹³C values of saturated hydrocarbons(average=-20.5‰)suggest that the upper Miocene lacustrine shale is the most likely candidate.Oleanane index(<5% in our samples)does not exclude either source rock possibility,and C₂₈/C₂₉ regular sterane(average=0.63)may be biased by high terrestrial inputs in a lacustrine setting.Together,our data show that northern and southern oils originate from the same source rocks but different oil kitchens.Given the similar geochemical characteristics of southern and northern oils,previous exploration successes in the northern subbasin likely suggest similar potential in the southern sector,while other elements influencing exploration success must be also evaluated.