有机岩石学研究有机质类型和成熟度的改进

作者对我国两个盆地的43个干酪根和煤包体样品进行了有机岩石学研究。用透射光、反射光和荧光相结合的方法进行了显微组份定量,测定了荧光光谱和镜质体反射率,并建立了荧光参数与镜质体反射率的关系图版。结果表明,通常所用的类型指数划分干酪根类型的方法存在很大的缺陷。无定形为主的干酪根可以属于任何一种化学类型,它的富氢程度取决于其来源及沉积和早期成岩环境,荧光方法可以有效地区分富氢和贫氢无定形,建立干酪根的光学分类与元素分析的关系;另外一些干酪根样品的镜质体反射率异常低(系吸附效应的结果),不能反映有机质成熟度,荧光参数可以弥补R°的不足,建立荧光参数与R°的关系图版,用荧光参数推测镜质体反射率值。      

库车坳陷煤生物标志物组成随成熟度的变化特征

对塔里木盆地库车坳陷三叠系和侏罗系的11个岩心与露头煤样的地球化学分析表明，煤的生物标志物组成随演化程度的增加而有规律的变化：成熟早期（镜质组反射率Ro／1．0％）煤的生物标志物组成反映了沉积环境和生源的特征；成熟晚期（1．10％＜Ro＜1．30％）煤的生物标志物特征受成熟度的控制作用十分明显，生物标志物参数随Ro的增大而增加或减小；高－过成熟阶段（Ro＞1．30％)所有煤样的生物标志物组成已基本趋于一致，而且和湖相泥岩的生物标志物特征相似，该阶段的生物标志物参数不能用来进行油源对比。     

煤系烃源岩热模拟演化过程的地球化学参数特征――以准噶尔盆地侏罗系煤系烃源岩为例

在准噶尔盆地侏罗系煤系烃源岩热模拟实验研究中 ,经过对原样和不同温度点热模拟残余物进行可溶有机质抽提和族组成分析、残渣干酪根处理、Ro 值测定和 TOC测定 ,并对部分样品系列进行色谱和质谱分析后发现 ,煤系烃源岩在不同热演化阶段表现出的地质地球化学特征具有相当大的差异。低演化阶段和热降解阶段天然气的形成是不同热力学条件和成气母质化学反应的结果。在低演化阶段 ,源岩镜质组反射率增长幅度并不太大 ,通常 Ro<0 .7%。原始可溶有机质和热模拟残余可溶有机质的分析结果表明 ,烃类气主要来源于原始可溶有机质的脱基团作用和大分子沥青质及干酪根边缘烃 (极性组分 )的热降解。在有机质热降解―热裂解阶段 ,烃源岩经地质埋深增温 ,热演化进程相对加快、镜质组反射率迅速递增、Ro 值从 0 .5 5 %～ 0 .70 %迅速增大到 1 .40 %～1 .70 % ,可见热动力作用足以破坏干酪根结构烃并将其降解形成油气。该阶段是干酪根经热降解大量排烃的阶段 ,其地球化学参数特征主要表现为干酪根结构烃热降解产物的特征。     

中国南方海相烃源岩生烃过程动力学研究

利用Rock-Eval 6热解仪和Optkin动力学软件对中国南方不同类型海相烃源岩和浮游藻进行了生烃动力学分析。研究表明,海相烃源岩的生烃平均活化能表现为EAⅠEAⅡ1EAⅡ2EAⅢ,在干酪根转化率10%~90%的有效生烃期间,生烃活化能跨度ΔE呈ΔEⅢΔEⅡ2ΔEⅡ1ΔEⅠ,最大生烃速率呈VmⅠVmⅡ1VmⅡ2VmⅢ;浮游藻生烃活化能很低,可在未熟—低熟期大量生成重质油。结合热模拟实验和模拟残样动力学分析认为,海相烃源岩的生烃动力学过程可以分为4个阶段:重质油形成阶段,Ro值在0.3%~0.6%,生烃平均活化能在220 kJ/mol左右,小于250 kJ/mol;正常原油形成阶段,Ro值在0.6%~1.2%,生烃平均活化能在250~270 kJ/mol左右;凝析油和天然气生成阶段,Ro值大于1.2%,生烃平均活化能大于270kJ/mol;干酪根生气死亡线,Ro值大于4.21%,生烃平均活化能大于320 kJ/mol。图4表4参19     

超压地层中镜质组反射率的计算

已有的研究表明,超压可以抑制镜质组的热演化、增加反应活化能。在EASY%R0模型的基础上,通过超压调节化学动力学反应活化能,建立了超压条件下镜质组热演化的化学动力学模型Pa％R0,并根据黄骅坳陷歧北洼陷受超压抑制和未受超压抑制的R0实测资料,确定了有关模拟参数。歧北洼陷港深48井明显超压(压力系数1．2～1．6),用Pa％R0模型所预测的有机质成熟度和生烃时间与用EASY%R0模型预测的明显不同,超压对R0的抑制可达0．1％～0．3％,可使烃源岩进入生油门限的时间推迟1～4．4Ma。图2参34     

四川盆地乐山—龙女寺古隆起地区震旦系储层沥青地球化学特征及意义

通过对四川盆地乐山—龙女寺古隆起地区储层沥青样品进行全岩镜下测定,发现该区震旦系灯影组储层中存在大量储层沥青,并对样品进行沥青反射率测定、有机元素分析和碳同位素分析,结果表明:古隆起地区震旦系灯影组储层沥青等效镜质体反射率(R′_O)值分布在2.06%~3.0%之间,平均值为2.62%,储层沥青H/C原子比和O/C原子比仅为0.30~0.43和0.01~0.03,表明沥青的成熟度高,基本上处于成熟—过成熟阶段,生烃潜力较低;S/C原子比为0.03~0.06,与长兴组(P₂ch)和飞仙关组(T₁f)储层沥青S/C原子比相比偏低,表明古隆起地区灯影组储层沥青受硫酸盐热化学还原反应(TSR)影响较小;此外,储层沥青碳同位素值分布在-36.8‰~-34.5‰之间,平均值为-35.7‰,在四川盆地各层位干酪根和沥青碳同位素值中其值最低,比塔里木盆地海相原油的碳同位素值还要低。结合四川盆地地质构造背景,对比各层位烃源岩干酪根碳同位素,认为古隆起地区震旦系灯影组储层沥青主要来源于下寒武统筇竹寺组烃源岩,属古油藏深埋时在高温、高压作用下裂解成气后的热演化沥青—焦沥青。     

RELATIONS BETWEEN DEPTH OF BURIAL, VITRINITE REFLECTANCE AND GEOTHERMAL GRADIENT

In wells where the drilled sequence is now at its maximum temperature, relations between depth and vitrinite reflectance show three segments: an upper segment with a linear gradient from 0.2–0.25% Ro at the surface to 0.6–0.7% Ro; a middle segment in which reflectance increases rapidly to c. 1.0% R; and a lower segment in which the gradient is again linear but reflectance increases more rapidly than in the upper segment. With a linear scale for depth, the inflection represented by the short middle segment tends to be obscured by the adoption by some authors of a log scale for reflectance.
The depth to the inflection systematically increases with decrease in geothermal gradient, allowing the development of a general diagram relating depth, reflectance and geothermal gradient. In wells where erosion is probable either at the present-day surface or at an unconformity, the general diagram can be used to estimate former maximum depths of burial and paleogeothermal gradients. These estimates, together with the presence of the inflection in the depth/reflectance relation, should be part of the input into modelling of the thermal history of sedimentary basins when reflectance is used in the model. The inflection is the result of the changing chemistry of vitrinite during oil generation, and the contrast between the depth/reflectance gradients above and below the inflection comparably reflects the contrast in vitrinite chemistry.     

源岩生烃潜力的有机岩石学评价方法

以酒东盆地侏罗-白垩系为例,介绍一种根据干酪根和(或)有机显微组分在源岩中的含量和“富氢组分/贫氢组分”值,结合镜质组反射率R0值和源岩果计厚度多项参数,采用计分定量化单井剖面、不同构造单元或同一凹陷内部烃源岩生烃潜力的对比评价方法.     

煤和不同主岩干酪根镜质组反射率差异性的研究

主岩岩相对其中的有机碎屑的镜质组反射率的影响,是应用上的一个重要问题。我们在淮北矿区对石炭二叠纪含煤地层中的煤和几种主要岩石中的干酪根作了反射率测定,同时对分散有机质镜质组反射率数据处理和取值的方法作了具体的研究。结果表明,与同层位煤的镜质组反射率相比,泥岩、砂岩和灰岩的镜质组反射率的变化幅度分别为+6—-10%、-1—-16%和+4—-14%。另外,从某种意义上说,对分散有机质而言,反射率数据处理与取值的方法比反射率测量本身更为重要。      

川中-川南过渡带须家河组烃源岩特征

川中-川南过渡带上三叠统须家河组可供勘探面积大,以此作为目的层的探井少,研究程度低。从有机碳含量、氯仿沥青“A”含量、 干酪根显微组分特征、干酪根碳同位素组成特征、镜质体反射率等方面着手,分析了研究区须家河组烃源岩有机质丰度、有机质类型和有机质成熟度,并对研究区烃源岩进行了初步评价。分析认为该区须家河组烃源岩总体属于中等-较好烃源岩,有机质类型以腐殖型为主,煤及泥岩大多仍处于成熟阶段为主的生烃高峰期。总体上须家河组有一定的生烃物质基础,有望获得较好的勘探效果。     

大北—克拉苏构造带盐下天然气识别

库车坳陷大北—克拉苏构造带天然气经历过深埋高温作用,为了判定盐下天然气的母质类型和成因类型,根据镜质体反射率的计算公式和金刚烷与成熟度的关系计算成熟度;依据Behar关系图谱和碳同位素值图谱识别裂解气类型。通过地球化学数据最终计算出Ro达到1.5以上,达到裂解气的形成条件;裂解气类型为干酪根裂解气。并且进一步证实干酪根类型为自由型干酪根,与黏土矿物的催化关系不密切;从干酪根的聚集类型可证实为聚集型干酪根而非可溶有机质。综合分析得出大北—克拉苏构造带盐下天然气为腐殖型+依附型+聚集型干酪根裂解气。     

HYDROCARBON SOURCE POTENTIAL AND MATURATION IN EOCENE NEW ZEALAND VITRINITE-RICH COALS

The results of traditional methods of coal characterisation (proximate, specific energy, and ultimate analyses) for 28 Eocene coal samples from the West Coast of New Zealand correspond well with biomarker ratios and Rock-Eval analyses. Isorank variations in vitrinite fluorescence and reflectance recorded for these samples are closely related to their volatile-matter content, and therefore indicate that the original vitrinite chemistry is a key controlling factor. By contrast, the mineral-matter content and the proportion of coal macerals present appear to have had only a minor influence on the coal samples' properties.
Our analyses indicate that a number of triterpane biomarker ratios show peak maturities by high volatile bituminous A rank; apparent maturities are then reversed and decline at the higher medium volatile bituminous rank.
The Rock-Eval S1+ S2 yield also maximizes by high volatile bituminous A rank, and then declines; however, this decline is retarded in samples with the most hydrogen-rich (perhydrous) vitrinites.
These Rock-Eval and biomarker trends, as well as trends in traditional coal analyses, are used to define the rank at which expulsion of gas and oil occurs from the majority of the coals. This expulsion commences at high volatile A bituminous rank, and persists up to the threshold of medium volatile bituminous rank(c. 1.1% Ro ran. or 1.2% Ro max in this sample set), where marked hydrocarbon expulsion from perhydrous vitrinites begins to take place.     

六盘山盆地马东山组低熟泥页岩有机质类型划分

以六盘山盆地马东山组湖相低熟泥页岩为研究对象,通过干酪根显微组分鉴定、岩石热解、饱和烃色谱—质谱分析等方法,对马东山组有机质类型特征及划分方案进行分析。综合分析表明：六盘山盆地马东山组低熟泥页岩有机质母质来源以水生浮游动植物和藻类为主,高等植物输入有限;干酪根显微组分鉴定显示其具有腐泥组和壳质组含量高、镜质组和惰质组含量低的特征,干酪根类型指数指示有机质干酪根类型为I型和II型。壳质组和腐泥组直接影响马东山组泥页岩品质和生烃潜力。各干酪根类型划分方案结果显示,对于马东山组低熟露头泥页岩干酪根类型的划分,干酪根显微组分鉴定、氯仿沥青“A”族组分、生物标志化合物划分结果相对一致且与母质来源一致,说明其适用性更好;比较而言,热解参数划分则出现明显的交叉、跨类等差异性,其适用性相对较差。     

干酪根及黏土单矿物对甲烷吸附能力的差异性

页岩气主要以游离气和吸附气的形式存在于富含有机质的泥页岩中。目前,国内外在干酪根和黏土矿物对甲烷吸附能力的差异性研究方面还比较薄弱。由此提出了将干酪根和黏土矿物进行分离的方法,对干酪根和不同黏土矿物分别进行等温吸附实验,研究单位质量的干酪根、伊蒙混层、高岭石、绿泥石和伊利石对甲烷吸附能力的差异性。结果表明:对甲烷吸附能力大小的次序为干酪根> 伊蒙混层> 高岭石> 绿泥石> 伊利石,有些样品干酪根吸附气量大于黏土矿物之和的吸附气量。随着温度的升高,干酪根和黏土单矿物对甲烷分子的吸附量有所下降。在同一温度下,干酪根吸附气量随镜质体反射率增大而增加,黏土矿物基本不受镜质体反射率的影响。      

苏北盆地下第三系烃源岩热演化研究

本文应用多种光学和化学标志,对苏北盆地下第三系烃源岩有机质热演化特征和阶段进行了研究。研究表明,(1)镜质组反射率Ro是最可靠的演化标志;(2)孢子体和藻类体的荧光变化规律相同,均具有特殊重要的演化意义;(3)随热演化程度的增加,烃源岩可溶有机物成分和结构发生显着变化;(4)苏北盆地有机质热演化阶段划分为阶段Ⅰ和阶段Ⅱ,其界线出现在Ro0.60%～0.65%,并揭示出不同构造单元有机质热演化的不均衡性。      

基于笔石表皮体反射率和拉曼光谱评价海相页岩热成熟度的方法

五峰组（O₃w）-龙马溪组（S₁l）海相页岩是川南下古生界页岩气勘探的主力层系之一,热成熟度是烃源岩和页岩气评价的一项重要指标。由于缺乏镜质体,一直难以建立准确评价下古生界海相页岩热成熟度的方法。共采集33块川南五峰组-龙马溪组岩心样品,用于观察源内固体沥青及笔石表皮体的光学特征,并测试其随机反射率。同时,利用样品中干酪根的拉曼光谱参数分析热成熟度的演化趋势。研究结果表明,相较于源内固体沥青,笔石表皮体来源单一、颗粒较大、特征明显,且垂直层理切面上非粒状笔石表皮体随机反射率（GR_or）数值分布更集中,更适合作为反射率测试对象。干酪根的拉曼光谱参数特征表明,热演化过程中GR_or与等效镜质体反射率（EqR_o）并非单一的线性关系。利用干酪根的拉曼光谱参数为中间变量,建立了通过GR_or计算EqR_o的方法。计算结果表明,五峰组-龙马溪组页岩在长宁、泸州-大足和威远地区的热成熟度依次降低,EqR_o分布范围分别为2.99 %~3.91 %,2.87 %~3.54 %和2.46 %~3.03 %,平均值分别为3.44 %,3.22 %和2.77 %。长宁西部出现了异常高成熟度区域,需要评价其对页岩气勘探的影响。     

A REASSESSMENT OF THE RANGE OF KEROGEN MATURITIES IN WHICH HYDROCARBONS ARE GENERATED

The ranges of vitrinite reflectance values, defining zones in which oil and gas generation occur, are examined from several points of view. Geochemical consideration of coalification reactions, kerogen compositions, iso-reflectance lines, spore colour and fluorescence, electron-spin resonance, extract data and reservoir temperatures point to the following approximate ranges: oil generation 1.0–2.0% R_o, wet gas and condensate 1.5-3.0% R_o, methane 2.0–5.0 % R_o. Biogenic methane can be formed at < 0.6% R_o. and hydrogen generation from kerogen appears to be possible above 5.0% R_o. These results point to hydrocarbon generation under hotter, deeper conditions than those proposed in most previous schemes. As a consequence, reflectance ranges are broadened for traces of vitrinite in possible reservoirs: oil < 0.4-1.3% R_o, methane < 0.4-3.0% R_o     

THE CAUSE AND MECHANISM OF VITRINITE REFLECTANCE ANOMALIES

The unexpected phenomena that measured vitrinite reflectance (Ro) values are lower (suppression) or higher (enhancement) than expected values at a given regional rank are defined as vitrinite reflectance anomalies. Such phenomena have been found in many basins in China, both in coal seams and in oil source rocks, and representative examples are presented in this paper. The cause and mechanism of vitrinite reflectance anomalies have been investigated by comparing the hydrogen contents and chemical structure of vitrinite macerals from immature Type I, Type II and Type III kerogens, and by studying the effects of early diagenetic oxidation on the thermostability of humic organic matter (OM). The results demonstrate: (1) depending on the anoxic or oxic nature of the depositional conditions, that lignocellulosic tissues can form a series of vitrinite macerals with different initial hydrogen contents and slightly different initial reflectivities; (2) that vitrinite macerals with different initial hydrogen contents have different reaction kinetics, with hydrogen-poor, oxygen-rich vitrinite maturing at an enhanced rate compared to vitrinite with a higher hydrogen content and a lower oxygen content; (3) that variations in the hydrogen content and the thermostability of vitrinite macerals are the main causes of Ro suppression and enhancement.     

ORGANIC FACIES OF EARLY CRETACEOUS SYNRIFT LACUSTRINE SOURCE ROCKS FROM THE MUGLAD BASIN, SUDAN

Cuttings samples from eight wells in the Muglad Basin have been analysed using a combination of organic geochemistry and palynofacies. The lacustrine Aptian-Albian shales of the Abu Gabra Formation, previously identified as the main source rock, have an overall mean TOC of 1.43% (n = 146), with those from the NW part of the basin (Sharaf area) being approximately twice as organic-rich as those from the SE (Heglig area). The Abu Gabra Formation contains two distinct organic facies: a lower interval dominated by higher TOC values (1.5–2.3%), higher measured hydrogen indices (338–546), higher amorphous kerogen contents (>80%), and heavier δ¹³C_TOC values (> −27%₀); and an upper, less rich interval (mean TOC 1.4%, mean HI 83, δ¹³C_TOC approximately −28%₀). The isotopic contrast between the upper and lower units may potentially be of stratigraphic use. The organic facies differences appear to reflect deteriorating preservation of the organic matter (higher dissolved oxygen, possibly due to shallower conditions resulting from lower rates of subsidence). Use of S2 v. TOC plots suggests corrected true mean hydrogen indices of around 800 in the richer facies (corresponding to a Type I kerogen). Mean random vitrinite reflectance, pyrolysis Tmax values, and visually determined fluorescence colours indicate that the samples studied are mostly immature, or at most in the earliest part of the oil window (<0.7% VR_o); biomarker data suggest that the vitrinite reflectance values may be suppressed by up to 20%.     

用漫反射光谱测定方法研究干酪根成熟度

用紫外／可见光／近红外漫反射光谱仪测定济阳均陷东营凹陷沙河街组8个干酪根样品的漫反射光谱，发现在波长600-1000nm范围，谱线的斜率与镜质体反射率(0．27%-0．67%)之间有很好的线性负相关关系。干酪根的漫反射光谱测定有可能成为评价有机质成熟度的一种筒单、快速、定量的新方法。图3表1参12