天然气地质学

南祁连盆地木里坳陷中侏罗统烃源岩原始有机碳含量恢复及与微孔隙演化的相关性

  • 刘世明 , 1 ,
  • 谭富荣 , 2 ,
  • 唐书恒 1 ,
  • 王金喜 3 ,
  • 王伟超 4 ,
  • 李永红 4
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  • 1. 中国地质大学(北京)能源学院,北京 100083
  • 2. 陕西省矿产地质调查中心,陕西 西安 710068
  • 3. 河北省资源勘测研究重点实验室,河北 邯郸 056038
  • 4. 中国煤炭地质总局,北京 100038
谭富荣(1984-),男,陕西西乡人,高级工程师,硕士,主要从事含油气盆地分析研究. E-mail: .

刘世明(1984-),男,陕西靖边人,高级工程师,博士,主要从事非常规油气地质研究. E-mail: .

收稿日期: 2020-10-20

  修回日期: 2020-12-23

  网络出版日期: 2021-07-22

Restoration of “original organic carbon content” and its relationship with micropore evolution of the Middle Jurassic source rock in the Muli Depression, Southern Qilian Basin

  • Shi-ming LIU , 1 ,
  • Fu-rong TAN , 2 ,
  • Shu-heng TANG 1 ,
  • Jin-xi WANG 3 ,
  • Wei-chao WANG 4 ,
  • Yong-hong LI 4
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  • 1. School of Energy Resource,China University of Geosciences,Beijing 100083,China
  • 2. Shaanxi Mineral Resources and Geological Survey,Xi’an 710068,China
  • 3. Key Laboratory of Resource exploration Research of Hebei Province,Handan 056038,China
  • 4. China National Administration of Coal Geology,Beijing 100038,China

Received date: 2020-10-20

  Revised date: 2020-12-23

  Online published: 2021-07-22

Supported by

The National Natural Science Foundation of China(41702144)

Fundamental Research Funds for the Central Universities(2652018234)

本文亮点

泥页岩有机质碳含量(TOC)是页岩油气评价的重要参数之一。然而,受有机质热演化生排烃影响,利用现今TOC评价与预测页岩油气资源时会出现一定的偏差。因此,进行烃源岩原始有机碳恢复对油气资源评价具有重要意义。木里坳陷位于南祁连盆地东北部,陆相中侏罗统广泛分布。中侏罗统为一套湖泊—三角洲相沉积的细粒碎屑岩,发育多套厚层富有机质暗色泥页岩,生烃潜力巨大。该层段内油气资源丰富,页岩有机质从低成熟到高成熟阶段均有分布,为原始有机碳含量的恢复提供了必要条件。以木里坳陷中侏罗统富有机质页岩为研究对象,利用岩石热解数据,采用物质平衡法有机碳恢复模型,对中侏罗统页岩原始有机碳含量进行了恢复。结果表明,中侏罗统页岩原始TOC含量与现今TOC含量的比值介于1.04~1.62之间,且随着热演化程度增高,比值变大。现今TOC含量与有机质孔隙发育之间没有必然的联系,然而,原始TOC含量与现今TOC含量之间的比值可以间接判断页岩有机质微孔隙发育情况。木里坳陷侏罗系页岩有机质类型以Ⅱ型和Ⅲ型为主,热演化参数(T max)大于440 ℃时,烃类转化率和排烃率都大于40%。相比样品矿物(石英和黏土矿物)含量、T max参数和现今TOC含量,原始TOC含量与页岩兰氏体积拟合性更好,结合热解参数T max,可以更好地判断页岩油气的吸附能力。因此,开展木里坳陷中侏罗统烃源岩原始有机碳含量恢复的研究,可以为木里坳陷烃源岩评价提供理论基础;同时对木里坳陷油气资源勘探提供新的思路。

本文引用格式

刘世明 , 谭富荣 , 唐书恒 , 王金喜 , 王伟超 , 李永红 . 南祁连盆地木里坳陷中侏罗统烃源岩原始有机碳含量恢复及与微孔隙演化的相关性[J]. 天然气地球科学, 2021 , 32(7) : 982 -992 . DOI: 10.11764/j.issn.1672-1926.2021.01.004

Highlights

Organic carbon content (TOC) of shale is one of the significant parameters for shale oil and gas assessment. However, the generation and expelling of hydrocarbons in shale was influenced by thermal evolution of organic matter, and a certain deviation occurred using present TOC to evaluate and predict shale oil and gas resources. Therefore, the restoration of original organic carbon from source rocks is of great significance for the evaluation of oil and gas resources. The Muli Depression, located in the northeast of the Southern Qilian Basin, was widely developed the Middle Jurassic continental shale. The Middle Jurassic is composed of a set of fine clastic rocks deposited in the lacustrine and delta setting. Multiple sets of thick dark organic-rich shales were developed, which have great hydrocarbon generation potential, and are found with abundant petroleum resources, and the thermal maturity of organic matter was from low maturity to high maturity, which provides the necessary conditions for the restoration of the original organic carbon content. In this paper, the original organic carbon content of Middle Jurassic shale in Muli Depression was calculated by material balance method using rock pyrolysis data. The results suggest that the ratio of original to present TOC content of the Middle Jurassic shale is between 1.04 and 1.62, and increases with the higher thermal maturity. No obvious relationship between the present TOC content and the pore development of organic matter in the Middle Jurassic shale. However, the difference between original and present TOC content could effectively assess the development of the micropores of organic matter in shale. The organic matter is mainly types Ⅱ and Ⅲ with thermal evolution (T max) greater than 440 ℃, and the transform and expulsion of hydrocarbons is greater than 40%. Compared with the minerals content (quartz and clay minerals content), T max and present TOC content, the original TOC content has a better correlation with the shale Langmuir volume, which combined with T max, could be more reasonable to evaluate the shale oil and gas adsorption capacity. Therefore, the original organic carbon content provides theoretical basis for source rocks evaluation, as well as a new idea for oil and gas exploration in the Muli Depression.

0 引言

有机碳含量(TOC)不仅是评价烃源岩生烃潜力的重要参数,也是衡量有机质孔隙发育的重要指标1-2。目前,国内外对烃源岩评价主要采用现今(残余)TOC指标3-4。残余有机碳含量对于未成熟烃源岩而言可以反映其原始生烃潜力,随着热演化程度的增高,干酪根不断向烃类转化,残余有机碳含量逐渐减低,难以真实客观地反映烃源岩的原始生烃潜力5。“原始TOC”指成岩过程中沉积岩中的有机质经历复杂生物化学及化学变化,通过腐泥化及腐质化过程形成干酪根后,未开始热解生烃或只热解生成极少量的烃类(不包括生物降解生烃),其岩石热解参数T max不大于400 ℃。近年来,我国在前震旦系和震旦系中发现大型油气藏,其中部分气源来自于残余有机碳较低、热成熟度较高的烃源岩6-7。因此,利用现今TOC含量评价烃源岩生烃潜力时会出现一定的偏差,尤其是高成熟—过成熟阶段的烃源岩,现今TOC含量较原始TOC含量明显降低8。随着热演化程度增高,干酪根持续热解生烃,有机质产生大量的微孔隙9-11,从而形成有利于页岩油气富集的甜点区。随着陆相页岩油气和古老油气藏勘探成果的不断涌现,对于高成熟或过成熟烃源岩初始生烃潜力有待重新认识。木里坳陷中侏罗统油气资源丰富,页岩有机质从低成熟到高成熟阶段均有分布,为进一步扩大油气找矿成果,有必要开展原始有机碳含量恢复。
以往恢复初始有机碳含量的方法主要有自然演化剖面法12、热解模拟法13、物质平衡法14-15等。这些方法都需要一定的假设条件,所以都存在一定的局限性。例如自然剖面法要求烃源岩热成熟度变化范围较大,单一盆地中很难找到合适的剖面。PETERS等13利用岩石热解数据建立热解模拟法估算初始有机碳含量,在质量平衡计算中引入生产指数修正因子,但是未考虑样品损失的气体和挥发的轻烃碳含量,导致估算的初始有机碳含量偏低。此外该方法还需对初始氢指数和生产指数进行适当的假设16。MODICA等15基于生烃动力学和热成熟度提出了物质平衡法,然而该方法隐含了一个基本假设,即页岩初始有机碳计算过程中未考虑游离烃碳含量。CHEN等14进一步完善了物质平衡法理论,考虑页岩中滞留烃对有机碳恢复的影响,提出原始有机碳含量由2个部分组成:①烃源岩中现今有机碳含量;②热演化过程中,烃源岩排出烃中的有机碳。该方法从物质平衡的角度出发,利用岩石热解数据,考虑了烃源岩排烃对原始TOC含量恢复的影响,使恢复的TOC含量更加接近原始TOC含量。
本文利用CHEN等14校正后的物质平衡法恢复木里坳陷中侏罗统页岩初始有机碳含量。数据来源为本文实验数据和已发表文献中热解数据。通过对比木里坳陷中侏罗统页岩原始TOC含量和现今TOC含量,揭露烃源岩原始生烃潜力,为寻找油气资源富集区提供新思路。

1 地质概况

南祁连盆地大地构造位于古亚洲构造域和特提斯域的结合部位17。整个南祁连盆地经历前石炭纪古大陆克拉通演化阶段、石炭纪—三叠纪新大陆克拉通化阶段和侏罗纪—第四纪残留盆地演化改造阶段18。南祁连盆地发育多套烃源岩层,含油气层系多,分布范围广,为一大型多旋回叠合含油气盆地。木里坳陷位于南祁连盆地东北部,作为南祁连盆地油气勘探的重点区域,呈狭长的北西西向展布,总体构造形态为复式向斜[图1(a)]。中侏罗世木里坳陷在区域性拉张作用下,沉积一套以陆相湖泊、三角洲相为主的含煤碎屑岩组合[图1(b)]。晚侏罗世受燕山运动影响,发生区域性抬升,气候变得炎热干旱,沉积面积大范围缩减。木里坳陷中侏罗统木里组和江仓组暗色泥页岩厚度大,分布稳定,有机质处于热生油气成熟阶段,具有良好的生油气潜力,该时段古气候温暖潮湿,沉积环境、陆源输入稳定,有机质以Ⅱ型和Ⅲ型干酪根为主19。木里组以深灰色泥岩和炭质泥岩为主,局部有煤层及细砂岩和粉砂岩;江仓组岩性组合更为多样,主要为煤层、细砂岩、粗砂岩和深灰色泥岩,上段发育有厚层的黑色油页岩,有机质丰度达6.0%以上。
图1 木里坳陷地质及利用钻孔分布

Fig. 1 Geological map and showing location of investigated cored wells of the Muli Depression

2009年9月,中国地质调查局在木里坳陷聚乎更地区成功获取了天然气水合物实物样品20,主要赋存于研究区冻土层下130~500 m的中侏罗统江仓组。天然气水合物资源丰富,在DK1、DK2、DK3和DK6等钻孔中发现油气显示(油斑、油浸、油迹),其与水合物产出层段一致或产出于水合物层段下部。表明中侏罗统烃源岩与水合物气源关系密切。有学者认为天然气水合物气源主要为中侏罗统富有机质泥页岩热解气21-22。玉门油田在木里坳陷实施木参1井和木参2井,中侏罗统均有良好的油气显示,有机质类型以Ⅲ型和Ⅱ2型为主,泥页岩生烃潜力达到好烃源岩,正处于生油气阶段23

2 原始TOC恢复方法与参数的确定

本文利用CHEN等14校正后的物质平衡法恢复木里坳陷侏罗系页岩初始有机碳含量。具体计算步骤为:①生烃转化率(T R)的估算;②排烃效率的估算;③恢复原始有机碳含量。
T R是衡量干酪根热解生烃的指标,是热成熟度和干酪根动力学特征的函数。有多种方法可以估算T R 13-1524,本文利用JUSTWAN等24提出的转化率公式(具体推导过程见附录1):
T R = 1   200 I H , O ( I H , O - I H ) ( 1   200 - I H )
该方程以干酪根最大理论生烃量(1 200 mgHC/gTOC,生成的烃类平均分子以C5为例,碳含量为83.33%)为计算值,T R为有机质生烃转化率; I H , O为原始氢指数; I H为现今氢指数;S 1为游离烃,S 2为热解烃。
根据现今样品质量,T R也可以表达为:
T R = S 1 + ε S 1 + S 2 + ε
式中:ε为烃源岩排出的烃量。
式(2)可知,排烃量(ε)可以表示为:
ε = S 2 T R 1 - T R - S 1
为估算排出烃的效率,引入排烃系数(f)。排烃系数为烃源岩排出烃与总生烃量的比值,主要有试验测量和盆地数值模型测量2种常用的方法25-26。本文根据岩石热解数据进行估算。
f = ε S 1 + ε = 1 - S 1 1 - T R S 2 T R = 1 - B i e ( 1 - T R ) I H T R
B ie=100×(S 1/CTOC),由JARVIE27提出,为含油饱和度指数;C TOC为现今TOC含量。样品岩石热解前,样品采集和存储过程中部分烃类气体难免会发生逸散,尤其是高成熟样品,由此会导致排烃系数增大。因此,在计算f值时,需要对S 1值进行校正。
根据质量守恒原理,现今有机碳含量为原始有机碳含量和排出的有机碳含量差值与岩石质量变化系数的比值:
C T O C = 1 φ ( C T O C - α C T O C , O f T R )
式中: C T O C , O 为原始有机质丰度,%;α为与干酪根类型相关的参数,为可转化碳与总碳含量的比值,α= I H , O/1 200; φ为质量转化因子,由现今的岩石质量比原始岩石质量( φ的具体推导过程见附录2)。
根据CHEN等14推算出的 φ公式为:
φ = 1 - I H , O 1   000 C T O C , O 100 f T R = 1 - 0.833 I H , O 1   200 C T O C , O 100 f T R = 1 - 0.833 α f T R C T O C , O 100
式(6)带入式(5),得出原始有机碳含量计算公式为:
C T O C , O = C T O C 1 - α f T R ( 1 - 0.833 C T O C / 100 )
本文研究在木里坳陷聚乎更地区ZK6-6、ZK7-3钻孔共采集泥页岩样品78件,所有样品均进行了岩石热解分析,部分样品开展了甲烷等温吸附、扫描电镜等实验;收集了DK10、DK7、ZK7-6、QH-2、木参1井等钻孔84件中侏罗统泥页岩热解数据192123。有机质类型以Ⅱ型和Ⅲ型为主,还有少量Ⅰ型干酪根(图2),生气潜力大;热演化程度范围为420~503 ℃,从未成熟到过成熟阶段均有分布。由于样品采集时间、挥发作用、样品处理和制备过程都不可避免地会造成轻质烃的损失,因此,按照未成熟、成熟和过成熟3个阶段对S 1的损失量进行校正;T max<430 ℃时,S 1参数按1.1系数进行恢复;430 ℃≤T max<480 ℃时,按1.35系数进行恢复;T max≥480 ℃时,按1.45系数进行恢复28。为确保热解数据的准确性29,本文以S 2>0.5 mg/g,T max>410 ℃和TOC>1.0%为标准剔除部分数据,最终可利用数据为141件,其中本文样品69件,前人样品72件。
图2 侏罗系页岩干酪根分类图

Fig.2 Classification map of Jurassic shale kerogen

根据木里坳陷中侏罗统泥页岩样品热解参数氢指数和T max可知,干酪根类型以Ⅱ型、Ⅲ型干酪根为主,还有少量Ⅰ型干酪根(图2)。烃源岩有机母质来源相同或相近时,随着热成熟度(T max)的增加,氢指数逐渐降低30。根据氢指数随热演化程度的变化趋势推断(图2),木里坳陷侏罗系烃源岩Ⅱ型、Ⅲ型干酪根原始氢指数( I H , O)约为530 mgHC/gTOC
基于实测热解数据得到的氢指数和推测的原始氢指数,生烃转化率(T R)根据式(1)可以直接算出。根据式(4),在已知氢指数和生烃转化率的基础上,利用岩石热解数据可以推算出烃源岩排烃系数(f)。T RT max的相关性可以定量表达生烃量随成熟度的变化,f值与T max的关系反映出排烃率的变化趋势(图3),从图3可以看出,有机质在T max值介于430~450 ℃之间时快速生烃,生烃转化率从0.2快速增加至0.9。同等条件下,T max值为440 ℃时,有机质内游离烃量达到最大(图4)。由图3可知,侏罗系烃源岩的排烃高峰期主要发生在T max值位于425~475 ℃之间,且具有早期排烃增速快(425~450 ℃),晚期增速呈下降或稳定趋势(450~480 ℃)的特征;推测可能与成岩压实作用和原油裂解生气的过程相关。
图3 木里坳陷侏罗系烃源岩有机质转化率和排烃率与热演化的关系

Fig.3 Relationship between organic matter conversion rate and hydrocarbon expulsion rate and thermal evolution of Jurassic source rocks in Muli Depression

图4 样品中单位有机碳游离烃含量与热演化的关系

Fig.4 Relationship between free hydrocarbon content per unit organic carbon and thermal evolution in samples

3 结果与讨论

木里坳陷中侏罗统富有机质泥页岩现今有机碳含量介于1.0%~8.4%之间,均值为2.5%。TOC含量主频发生在1%~3%之间,占比为76.5%(图5)。样品热解温度T max值位于420~503 ℃之间,均值为452 ℃。表明侏罗系页岩从低成熟到过成熟阶段均有分布,大多数样品达到了成熟阶段(图2图4)。南祁连盆地从二叠纪至中侏罗世,地温梯度逐渐升高(29~51 ℃/km),在中侏罗世晚期达到最大31,之后地温梯度逐渐降低(51~31 ℃/km)。
图5 TOC含量频率直方图

Fig.5 Frequency histogram of TOC content

侏罗系沉积后,在中侏罗世晚期快速沉降,此时地温梯度达到最大,烃源岩达到高成熟阶段(R O<1.3%)(图6图7)。受燕山运动和喜马拉雅造山运动影响,晚侏罗世至今木里坳陷处于缓慢抬升阶段32。中侏罗统烃源岩目前正处于生油气阶段(图6)。
图6 南祁连盆地二叠纪至侏罗纪烃源岩埋藏史—热史叠合图31

Fig.6 Overlay map of burial history and thermal history of Permian-Jurassic source rocks in southern Qilian Basin31

图7 南祁连盆地烃源岩热演化史31

Fig.7 Thermal evolution history of source rocks in southern Qilian Basin31

利用扫描电镜对木里坳陷中侏罗统泥页岩样品微孔隙进行观察,发现有机质孔隙发育及分布与热演化程度具有较高一致性。有机质从低成熟至成熟再到高成熟阶段,有机质孔隙对应为不发育、发育、似海绵针状密集发育(图8)。有机质孔隙发育主要受热演化程度和有机质丰度控制,页岩中油气储集、运移主要发生在有机质孔隙内32-33。但是现今有机碳含量与孔隙发育之间没有直接的相关性。例如,图8(a)和图8(b)样品热解T max值为430 ℃,现今TOC含量为4.6%,原始TOC含量为5.0%,有机质孔隙基本不发育。图8(c)和图8(d)样品有机质达到成熟阶段(T max值为450 ℃),现今TOC含量为3.2%,原始TOC含量为4.6%,有机质内发育形状不规则、大小不一的有机质孔隙。图8(e)和图8(f)为高成熟样品(T max值为480 ℃),现今TOC含量为3.8%,原始TOC含量为5.8%,页岩有机质发育似海绵针状孔隙,微裂隙也发育。因此,仅仅利用现今TOC含量不能判断页岩储层油气储集能力。有机质类型一致的条件下,原始TOC含量和现今TOC含量之间的比值可以有效评估有机质孔隙发育情况14
图8 侏罗系页岩不同成熟度样品SEM图像

Fig.8 SEM images of Jurassic shale samples with different maturity

基于以上原始TOC含量恢复参数的确定及各参数与热演化成熟度的相关关系,结合式(5)式(7),计算出木里坳陷侏罗系泥页岩原始TOC含量。与现今TOC含量对比发现(图9),两者比值最大为1.62,最小为1.04。受烃源岩热演化程度的影响,不同成熟度的样品恢复的原始和现今TOC含量变化差异较大(图9)。原始有机质随着成熟度的增加,生烃转化率逐渐增大(图3),因此高成熟度烃源岩原始TOC含量相对现今TOC含量变化较大。有机质孔隙发育随热演化程度的变化也说明了研究区有机质生烃的过程(图8)。对于成熟或高成熟的烃源岩,利用现今TOC含量评价其生烃潜力或圈定页岩油气有利区时,会导致部分有利层段被排除。例如,烃源岩现今TOC含量为1.0%,其原始TOC含量可能高达1.6%。
图9 侏罗系页岩现今TOC含量和原始TOC含量之间关系

Fig.9 Relationship between present TOC and original TOC of Jurassic shale

目前,祁连山冻土区天然气水合物勘探主要在木里坳陷聚乎更地区取得了突破,以往研究认为水合物气源主要来源于烃源岩热解气233134。本文对木里坳陷中侏罗统烃源岩原始有机碳含量进行了恢复,发现有机质热演化参数T max>440 ℃时,干酪根转化率和排烃率都大于40%。由此可知,木里坳陷中侏罗统烃源岩广泛发生生排烃过程,为油气聚集提供必要条件。
干酪根热解生烃,在此过程中产生大量微孔隙(图8),有机质表面具有亲油属性,因此,页岩有机质对油气具有较强的吸附能力,也是油气存储、运移的主要场所35-36。本文对木里坳陷中侏罗统页岩有机碳含量不同的样品开展等温吸附实验,总体来看,现今有机碳含量越大,甲烷吸附量随之增大(图10)。然而,现今TOC含量为1.9%的样品甲烷吸附量大于现今TOC含量为2.5%和2.8%的样品。由于原始TOC含量影响着干酪根孔隙和比表面积发育的潜力35。兰氏体积(V L)和原始TOC含量、现今TOC含量之间的关系如图11所示,原始TOC含量与V L具有更好的相关性。页岩兰氏体积与T max具有良好的正相关性,随着有机质热演化程度增高,干酪根转化率升高,造成现今TOC含量低,但有机质孔隙发育,为甲烷吸附提供了有利条件。兰氏体积与黏土矿物含量呈弱的相关性,与石英含量无相关性,表明黏土矿物具有弱的吸附能力(图12)。因此,利用原始TOC含量结合热演化参数可以更好地判断页岩吸附能力。
图10 木里坳陷侏罗系页岩等温吸附曲线

Fig.10 Isothermal adsorption curve of Jurassic shale in Muli Depression

图11 页岩兰氏体积与TOC含量的关系

Fig.11 Relationship between shale Langmuir volume and TOC

图12 页岩兰氏体积与T max(a)和矿物含量(b)的相关性

Fig.12 Correlation between shale Langmuir volume and T max (a)and mineral content(b)

4 结论

(1)根据原始TOC恢复模型和参数的确定,恢复了木里坳陷中侏罗统页岩原始TOC含量。发现页岩原始TOC含量与现今TOC含量比值位于1.04%~1.62%之间。有机质类型为Ⅱ型和Ⅲ型时,有机质热演化生烃在440 ℃时达到最大,随着有机质热演化程度的增加,原始TOC含量与现今TOC含量差异越大。
(2)木里坳陷中侏罗统烃源岩现今TOC含量与有机质孔隙发育之间不具有良好的相关性,然而,采用原始TOC含量与现今TOC含量的比值可以间接判断页岩有机质微孔隙发育情况和生烃大小。页岩有机质类型主要为Ⅱ型和Ⅲ型,T max大于440 ℃时,有机质转化率和排烃率都大于40%,表明木里坳陷具有较好的油气资源勘探前景。
(3)与现今TOC相比,原始TOCV L具有更好的相关性。样品热解参数T maxV L具有良好的相关性,原始TOC含量决定着有机质微孔隙发育潜力,有机质热演化程度影响着现今有机质孔隙的发育与分布。

干酪根转化率(T R)的推导过程:

假设M o为未成熟或低成熟烃源岩质量,其初始氢指数为 I H , O,有机碳含量为 C T O C , O ;热解生排烃后烃源岩剩余质量为M x,其氢指数为 I H,剩余有机碳含量C TOC。干酪根转化率(T R) 可表达为:

T R = ( I H , O C T O C , O M o - I H C T O C M x ) I H , O C T O C , O M o

式(8)中: I H , O C T O C , O M o代表烃源岩初始生烃潜力; I H C T O C M x代表烃源岩热演化生烃后残余有机质生烃潜力。因此, ( I H , O C T O C , O M o - I H C T O C M x )表示烃源岩烃类的生成量。式(8)也可以表示为:

T R = 1 - I H C T O C M x I H , O C T O C , O M o = 1 - I H I H , O ( C T O C M x C T O C , O M o )

有机质热演化过程中,以干酪根最大理论生烃量(每克干酪根碳可生成烃类1 200 mg)为计算标准,T R也可表示为:

T R = 1 200 ( C T O C , O M o - C T O C M x ) I H , O C T O C , O M o

式(10)中: 1 200 ( C T O C , O M o - C T O C M x )代表热演化过程中烃类的生成量,该公式也可表示为:

T R = 1 200 C T O C , O M o I H , O C T O C , O M o - 1 200 C T O C M x I H , O C T O C , O M o = 1 200 I H , O - 1 200 I H , O ( C T O C M x C T O C , O M o )

变换后得到:

1 200 I H , O ( C T O C M x C T O C , O M o ) = 1 200 I H , O - T R

式(12)两边同时乘以 I H , O / 1 200得到:

C T O C M x C T O C , O M o = 1 - I H , O 1 200 T R

式(13)带入到式(9)中计算得到:

T R = 1 - I H I H , O 1 - I H , O 1 200 T R = 1 - I H I H , O + I H 1 200 T R

变换后得到:

T R - I H 1 200 T R = 1 - I H I H , O
T R ( 1 200 - I H ) 1 200 = ( I H , O - I H ) I H , O

式(16)两边同时乘以1 200/(1 200 - I H)后得出:

T R = 1 200 I H , O ( I H , O - I H ) ( 1 200 - I H )

质量转化因子 φ的推导过程:

未成熟或低成熟烃源岩质量M o 是烃源岩热演化生排烃后的质量M x与排出烃的质量之和。f 为排烃系数,M o的推导公式如下:

M o = M x + I H , O 1 000 C T O C , O 100 M o f T R = M x + C T O C , O 100 I H , O 1 000 f T R M o

换算后得出:

M x = M o ( 1 - C T O C , O 100 I H , O 1 000 f T R )

质量转化因子 φ = M x / M o,与式(19)结合得到:

φ = M x M o = 1 - C T O C , O 100 I H , O 1 000 f T R

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