Characteristic of homodrimane and maturity of organic matter in the low mature source rocks

Bicyclic sesquiterpenoids are mostly used to illustrate the origins of organic matter and genetic types of crude oil presently.In this paper,the relationship between distributions and compositions of C16 homodrimane in immature to mature source rocks and evolution of organic matter was studied,and the correlation between C16 homodrimane at immature to low mature stages and thermal evolution of organic matter was analyzed.The results show that in terrestrial facies depositional system,the ratio of 8α(H)-homodrimane to 8β(H)-homodrimane has a high sensitivity about the maturity’s minor changes at immature to low mature stages.It is found that when the vitrinite reflectance R0<0.7%,the ratio significantly decreases with increasing burial depth or maturity.This kind of phenomenon reveals that these parameters may be the useful maturity indicators for determining the relative maturation of organic matter at immature to low mature stages,and have certain practical value in biogeochemical and en- vironmental geochemical research on low mature oil and gas.     

倍半萜类分布和组成与低熟烃源岩有机质热演化研究

通过对低成熟烃源岩中8α(H)-升补身烷和8β(H)-升补身烷以及2-乙基甲基四氢化萘和1-乙基甲基四氢化萘分布和组成特征的剖析,研究了8α(H)-升补身烷/8β(H)-升补身烷比值和1-乙基甲基四氢化萘/2-乙基甲基四氢化萘比值与镜质组反射率R°之间的关系,发现在R°＜0.60%时,这两个比值变化幅度很大,表明这两个比值在低成熟阶段是衡量有机质热演化程度的有效指标.     

中国煤和烃源岩镜质组的激光诱导荧光显微特征及其应用

应用自行组装的激光诱导荧光显微光度计(LIFM)系统地研究了中国煤和烃源岩中镜质组的荧光强度及荧光变化，建立了镜质组的荧光变化与成熟度之间的相关模式图(R-I-VRo)，该图可解决镜质组反射率抑制问题，并将烃源岩成熟度评价范围扩展到VRo达2．0％左右，该方法对于正确评价烃源岩成熟度具有广泛的应用前景。     

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。     

下古生界有机质成熟度评价新参数：笔石表皮体光学特征再研究

下古生界缺失高等植物来源的镜质组,其有机质成熟度的确定一直是油气源岩评价的难题之一。基于对含笔石页岩的反射光显微镜观察和低成熟度含笔石页岩与煤共置的热压模拟实验,研究了下古生界海相页岩笔石表皮体的光性特征及其热演化规律,探讨了笔石表皮体随机反射率作为有机质热演化参数的可行性。下古生界海相页岩非粒状笔石表皮体呈条带状顺层或者碎片状产出、颗粒较大,光学特征类似于镜质组,适合于测量反射率。非粒状笔石表皮体随机反射率■换算为等效镜质组反射率■的关系式为■。采用笔石表皮体随机反射率分析了上扬子地区东部五峰组—龙马溪组页岩的有机质成熟度分布特征,认为非粒状笔石表皮体随机反射率是一个实用的下古生界烃源岩有机质成熟度指标,为确定下古生界有机质成熟度提供了一种可信的解决方案。     

Organic matter maturation under the influence of a deep intrusive heat source: A natural experiment for quantitation of hydrocarbon generation and expulsion from a petroleum source rock (Toarcian shale, northern Germany)

Four shallow boreholes were drilled in the Hils syncline, northern Germany, in order to determine quantitatively the amount of hydrocarbons generated and expelled during maturation of a typical kerogen-type-II-bearing source rock. The holes penetrated the carbonceous Lias shales (Posidonia shale, Lower Toarcian) and part of the adjacent Dogger α and Lias δ mudstones. The maturity of the organic matter in the cores recovered ranges from immature (0.48% R̄₀) to overmature 1.45% R̄₀) due to location of the Hils syncline in the vicinity of the Vlotho Massif, which is deep-seated intrusive body. Facies variations of the Lias within the short geographical distances in the study area are negligible.Organic matter mass balance calculations were based on detailed organic geochemical analyses of residual material in the Lias shales (kerogen, bitumen etc.) and on the evidence of a uniform initial composition of these sediments in the study area. Dead carbon determinations supported this latter criterion but were not used as a parameter in the calculations.About 50% of the initial kerogen was transformed into oil, gas and inorganic compounds during the vitrinite reflectance increase from 0.48 to 0.88% R̄_o and only marginally more during the maturity increase from 0.88 to 1.45% R̄_o. Only a small portion of the generated material remained in the source rock even at a relatively early stage of generation (0.68% R̄_o). Expulsion efficiency of oil plus gas reached a value of 86% at the end of the main generation stage (0.88% R̄_o).     

Evaluation of the petroleum composition and quality with increasing thermal maturity as simulated by hydrous pyrolysis: A case study using a Brazilian source rock with Type I kerogen

Hydrous pyrolysis (HP) experiments were used to investigate the petroleum composition and quality of petroleum generated from a Brazilian lacustrine source rock containing Type I kerogen with increasing thermal maturity. The tested sample was of Aptian age from the Araripe Basin (NE-Brazil). The temperatures (280–360 °C) and times (12–132 h) employed in the experiments simulated petroleum generation and expulsion (i.e., oil window) prior to secondary gas generation from the cracking of oil. Results show that similar to other oil prone source rocks, kerogen initially decomposes in part to a polar rich bitumen, which decomposes in part to hydrocarbon rich oil. These two overall reactions overlap with one another and have been recognized in oil shale retorting and natural petroleum generation. During bitumen decomposition to oil, some of the bitumen is converted to pyrobitumen, which results in an increase in the apparent kerogen (i.e., insoluble carbon) content with increasing maturation.The petroleum composition and its quality (i.e., API gravity, gas/oil ratio, C₁₅₊ fractions, alkane distribution, and sulfur content) are affected by thermal maturation within the oil window. API gravity, C₁₅₊ fractions and gas/oil ratios generated by HP are similar to those of natural petroleum considered to be sourced from similar Brazilian lacustrine source rocks with Type I kerogen of Lower Cretaceous age. API gravity of the HP expelled oils shows a complex relationship with increasing thermal maturation that is most influenced by the expulsion of asphaltenes. C₁₅₊ fractions (i.e., saturates, aromatics, resins and asphaltenes) show that expelled oils and bitumen are compositionally separate organic phases with no overlap in composition. Gas/oil ratios (GOR) initially decrease from 508–131 m³/m³ during bitumen generation and remain essentially constant (81–84 m³/m³) to the end of oil generation. This constancy in GOR is different from the continuous increase through the oil window observed in anhydrous pyrolysis experiments. Alkane distributions of the HP expelled oils are similar to those of natural crude oils considered to be sourced from similar Brazilian lacustrine source rocks with Type I kerogen of Lower Cretaceous age. Isoprenoid and n-alkane ratios (i.e., pristane/n-C₁₇ and phytane/n-C₁₈) decrease with increasing thermal maturity as observed in natural crude oils. Pristane/phytane ratios remain constant with increasing thermal maturity through the oil window, with ratios being slightly higher in the expelled oils relative to those in the bitumen. Generated hydrocarbon gases are similar to natural gases associated with crude oils considered to be sourced from similar Brazilian lacustrine source rocks with Type I kerogen of Lower Cretaceous, with the exception of elevated ethane contents. The general overall agreement in composition of natural and hydrous pyrolysis petroleum of lacustrine source rocks observed in this study supports the utility of HP to better characterize petroleum systems and the effects of maturation and expulsion on petroleum composition and quality.     

The effects of surface area, grain size and mineralogy on organic matter sedimentation and preservation across the modern Squamish Delta, British Columbia: the potential role of sediment surface area in the formation of petroleum source rocks

Surface sediment samples were collected from the Squamish River Delta, British Columbia, in order to determine the role of sediment surface area in the preservation of organic matter (OM) in a paralic sedimentary environment. The Squamish Delta is an actively prograding delta, located at the head of Howe Sound.Bulk total organic carbon (TOC) values across the Squamish Delta are low, ranging from 0.1 to 1.0 wt.%. The carbon/total nitrogen ratio (C_org/N) ranges from 6 to 17, which is attributed to changes in OM type and facies variations. The <25-μm fraction has TOC concentrations up to 2.0 wt.%, and a C_org/N ratio that ranges from 14 to 16. The 53–106-μm fraction has higher TOC concentrations and C_org/N ratios relative to the 25–53-μm fraction. The C_org/N ratio ranges from 9 to 18 in the 53–106-μm fraction and 5.5–10.5 in the 25–53-μm fraction. Surface area values for bulk sediments are low (0.5–3.0 m²/g) due to the large proportion of silt size material. Good correlation between surface area and TOC in bulk samples suggests that OM is adsorbed to mineral surfaces. Similar relationships between surface area and TOC were observed in size-fractionated samples. Mineralogy and elemental composition did not correlate with TOC concentration.The relationships between surface area, TOC and total nitrogen (TN) can be linked to the hydrodynamic and sedimentological conditions of the Squamish Delta. As a result, the Squamish Delta is a useful modern analogue for the formation of petroleum source rocks in ancient deltaic environments, where TOC concentrations are often significantly lower than those in source rocks formed in other geological settings.     

HyLogger-3, a visible to shortwave and thermal infrared reflectance spectrometer system for drill core logging: functional description

Australian Geological Surveys are the custodians of a major national asset in the form of historically drilled and archived drill cores of the top few kilometres of the continent acquired by government agencies and companies over many decades. The AuScope National Virtual Core Library (NVCL) component of the AuScope Earth Model comprises geological/rock samples, technology, people and database/delivery infrastructure located in six nationally distributed nodes and is aimed at extracting additional value from this asset. The technology components of the NVCL comprise an integrated suite of hardware (HyLogger-3) and software (TSG-Core) systems for the imaging and hyperspectral characterisation of drill cores in their original core trays and the interpretation of their contained oxide, carbonate, hydrous and anhydrous silicate mineralogy. The HyLogger-3 includes state-of-the-art Fourier Transform Spectrometers that continuously measure calibrated spectral reflectance from nominal 10 by 18 mm fields of view. These spectra are in turn passed through a series of automatic and semi-automatic pre-processing and mineralogical unmixing algorithms. These, along with numerous other tools in TSG-Core, output a variety of mineralogical and image products for use by scientists in many branches of the earth sciences. This paper provides a functional overview of the HyLogging hardware and software tools available in each of Australia's Geological Surveys.