西加盆地烃源岩自然演化与热模拟地球化学特征对比研究

发布时间：2018-12-18 02:40

【摘要】：论文选取西加拿大沉积盆地科罗拉多群Second White Specks(2WS)组不同埋深、从未成熟到高成熟的烃源岩样品,建立一个完整的自然演化系列;同时,采集两件吉林桦甸盆地新生代古近系油页岩样品,与一件低熟的西加样品进行高压釜热压模拟实验,建立了人工熟化序列。在比较不同地区的样品在相同的实验条件下有机地球化学特征变化的同时,还对西加盆地样品的自然演化和热模拟实验条件下的地球化学特征进行了对比研究,全面刻画有机质热演化过程。本次所选西加盆地样品有机质类型以II型干酪根为主;有机质丰度较高,分布范围广,以原地生成为主。随着埋深的增大,样品中游离烃(S1)逐渐升高并在2600米左右达到最大值,裂解烃(S2)则由于转化为游离烃(S1)以及焦沥青,含量迅速减小;有机质成熟度随埋深的增加相应升高。通过对样品进行抽提、组分分离、饱和烃、芳香烃色谱-质谱分析,研究各类分子化合物的绝对含量以及各成熟度参数在自然演化剖面和热模拟过程中随成熟度不同呈现出的变化。从整体对比结果看,热模拟实验能够较好反映有机质演化历程,但部分结果仍与自然演化存在一定差异,反映时间与温度发挥作用不同,对比两种热演化体系可以全面深化对成烃机理的认识,各系列化合物绝对含量变化是刻画和重新认识成熟度体系的关键所在。通过研究部分样品的已知镜质体反射率Ro和甲基菲指数、烷基二苯并噻吩以及热解参数Tmax的相互关系,发现甲基菲指数(MPI-2)与Ro相关性最好,相关系数达0.93,因此采用甲基菲指数对大部分西加样品进行Ro的拟合,并对拟合出的Ro随深度的变化特征进行研究,发现Ro随着深度的变化,并不是通常所认为的线性变化,而是分为三个阶段:缓慢变化阶段、中等快速阶段和快速增加阶段。自然演化样品有机质转化率不同计算方法结果较为一致:埋深2000米之上的样品数值分布范围广,而当埋深达到2500米之后,有机质转化率逐渐达到稳定值。热模拟样品有机质转化率与北海Kimmeridgian源岩相似,均分为三个阶段,即缓慢增长阶段、快速增长阶段以及稳定阶段;然而不同计算方法结果却有较大差别:降解率法计算的有机质转化率初始就达90%以上;而斜率法计算的有机质转化率初始为36.6%,并且该方法计算的有机质转化率与样品的生排烃产率曲线有很好的对应关系,说明斜率法可以更好的体现热模拟样品有机质的生排烃过程。
[Abstract]:In this paper, the source rock samples with different burial depth and never matured to high maturity in the Second White Specks (2WS) formation of western Canada sedimentary basin are selected to establish a complete series of natural evolution. At the same time, two samples of Cenozoic Paleogene oil shale in Huadian Basin of Jilin Province were collected and simulated by autoclave with a low-mature sample of Xijia. The artificial maturation sequence was established. While comparing the changes of organic geochemical characteristics between samples from different regions under the same experimental conditions, the natural evolution of samples in the Xijia Basin and the geochemical characteristics under the conditions of thermal simulation experiments are also studied. A comprehensive description of the thermal evolution of organic matter. The main types of organic matter in Xijia basin are II kerogen, the abundance of organic matter is high, the distribution range is wide, and the origin of organic matter is mainly in situ. With the increase of buried depth, the free hydrocarbon (S1) in the sample increases gradually and reaches the maximum value at about 2600 m, while the pyrolysis hydrocarbon (S2) decreases rapidly because of its conversion to free hydrocarbon (S1) and pyrobitumen. The maturity of organic matter increases with the increase of buried depth. By extracting the sample, separating the components, analyzing the saturated hydrocarbon, and analyzing the aromatic hydrocarbon by chromatography-mass spectrometry, The absolute content of various molecular compounds and the variation of maturity parameters with different maturity in the natural evolution profile and thermal simulation process are studied. From the overall comparative results, the thermal simulation experiment can better reflect the evolution of organic matter, but some of the results are still different from the natural evolution, reflecting the time and temperature play different roles. Comparing the two thermal evolution systems can deepen the understanding of hydrocarbon generation mechanism in an all-round way. The change of absolute content of each series of compounds is the key to characterize and re-understand the maturity system. By studying the relationship between the known vitrinite reflectance (Ro) and phenanthrene index, alkyl dibenzothiophene and pyrolysis parameter Tmax, it was found that the correlation between MPI-2 and Ro was the best, and the correlation coefficient was 0.93. Therefore, using phenanthrene methyl index to fit the Ro of most samples in Siga, and studying the variation characteristics of Ro with depth, it is found that the variation of Ro with depth is not linear as generally thought. It is divided into three stages: slow change stage, medium fast stage and fast increasing stage. The results of different calculation methods for organic matter conversion of natural evolution samples are consistent: the sample above 2000 meters buried depth has a wide range of numerical distribution, but when the buried depth reaches 2500 meters, the organic matter conversion rate gradually reaches a stable value. The organic matter conversion rate of the simulated samples is similar to that of the North Sea Kimmeridgian source rocks, which is divided into three stages: slow growth stage, rapid growth stage and stable stage. However, the results of different calculation methods are quite different: the conversion rate of organic matter calculated by the degradation rate method is above 90%; And the conversion rate of organic matter calculated by slope method is 36.6, and the conversion rate of organic matter calculated by this method has a good correspondence with the hydrocarbon generation and expulsion yield curve of the sample. The slope method can better reflect the hydrocarbon generation and expulsion process of organic matter.
【学位授予单位】：中国地质大学(北京)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P618.13

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