生油岩之沈積環境及成熟度對生油之螢光屬性、多環芳香烴和生物指標的影響之實驗研究

Source dependence of fluorescence characteristics and aromatic, biomarker maturity parameters evaluated by artificial maturation.

張英如(Ying-Ju Chang)

指導教授 ： 黃武良

國立臺灣大學/理學院/地質科學研究所/博士(2010年)

https://doi.org/10.6342/NTU.2010.00819

摘要

螢光光譜能透露著有機物官能基的變異，同時又能指示成熟度的意涵，此外，對於油具有絕佳的辨別力，因此，螢光光譜為油屬性分析一有效工具。本研究除了針對傳統螢光屬性的探討，了解不同有機質在室溫和高溫下油母質及煤之螢光隨時間的變化(temporal fluorescence alteration; TFA)，以試圖了解溫度所扮演的角色，並進一步以透光性良好的鑽石砧實驗，利用連續觀察的方式，模擬包裹體在地層中所封存石油的特性，也因為觀測對象為直接由源岩產生的”活”油，更能直接突顯不同成熟度下油性質的異同，最後結合圍壓熱裂解實驗，氣相層析質譜儀進行成分分析，如此一來則能對比出生油反應過程中，油氣成分的變異，以及過去常用的生物指標之適用性。
經本研究可得以下之初步結果：(1)本研究直接印證螢光波長的變化主要受控於成熟度，實驗結果與前人研究中，以油包裹體之螢光推測螢光隨成熟度增加而往短波長偏移的現象相符合。本實驗進一步發現儘管油的來源不同，無論升溫速率為何、無論何種沈積環境之油母質，當螢光強度開始大幅躍升，其相對應之最大螢光強度波長(λmax)則開始往短波長方向偏移(blue-shift)，這樣的結果足以說明為何多數高成熟度的油包裹體以具偏藍螢光居多。本研究成果對瞭解油包裹體的螢光顏色所代表之意涵，提供直接之實驗證據。(2)螢光屬性在空氣中及在氬氣中呈現不同的變化，是由於光氧化作用和溫度的抑制效應。針對油母質尚未產生油之溫度對螢光的抑制效應(thermal quenching)的實驗中顯示，螢光強度呈現隨升溫而遞減，油母質的螢光遞減梯度，與前人量測原油之結果類似。在室溫下油母質的初始螢光強度(Finitial)與其氫指數(HI)、最大產油量之螢光強度(Fmax)成正相關，因此，可以利用量測油母質的初始螢光強度預測其產油潛能。膜煤素(Liptinites)之初始螢光和最大產油量之螢光強度均較鏡煤素(Vitrinite)和惰煤素(Fusinite)高，顯示煤中之膜煤素為主要產油成分。鏡煤素在1.2%Ro時，螢光強度達到最大值，隨後則逐漸遞減，因此，可藉由不同螢光特徵鑑別不同的煤素質。(3)就氣相層析質譜儀的分析結果中顯示，樞紐成分的碳數位置及烷烴的分布情形、以及奇偶數碳優勢比值隨著成熟度提升而趨近於1的程度能指示著有機物來源的異同訊息。芳香族類之分析結果中，皆可發現各成熟度指標受有機物來源環境的影響甚鉅，以硫芴化合物之成熟度參數MDR而言，對於即使同為海相源岩Bar及W其比值卻呈現隨著成熟度完全迥異的兩種趨勢。在菲系化合物之成熟度參數中，則會由於有機物來源不同而導致含有的菲系化合物含量上的差異，使得各計算參數結果有所不同，因此使用甲菲作為成熟度指標時，應特別留意有機物的沈積相。萘系化合物之成熟度參數中則以TNR-2、TMNr之計算結果隨成熟度而有較明顯的變化，MNR、DNR-1、TNR-1的計算結果中，湖相源岩GR在成熟度高於1.1%Ro之後比值才開始有顯著的升高，亦即為高成熟度的指標參數。在生物指標的圖譜分析中發現Pristane(Pr)/n-C17、Phytane(Ph)/n-C18比值均隨著成熟度升高呈遞減趨勢，遞減的程度取決於有機物來源的沈積環境，對同一來源的有機物樣品而言，其log(Pr/n-C17)和log(Ph/n-C18)隨著成熟度呈現平行於有機物類型的界線，兩比值隨成熟度具有同幅度的增減變化，亦即此兩比值能有效地判讀有機物來源而不受成熟度的影響。各樣品之Ts/Ts+Tm和Tetracyclic terpanes/αβ C30 hopane比值均可區分為隨成熟度升高而上升和下降兩種趨勢，比值中的化合物隨著成熟度升高的增減轉換情形與有機物的成分有關。在雙環類半三萜烷(bicyclic sesquiterpane)的成熟度指標中，Drimane、Homodrimane和Eudesmane含量多寡主要受控於有機物來源的沈積環境，從各比值的遞增或遞減趨勢，則能反映有機物在生油過程中反應趨向於生成該化合物或是裂解反應。

關鍵字

螢光 ； 多環芳香烴 ； 生物指標 ； 生油岩

並列摘要

The fluorescence spectroscopy has been widely used to estimate compositions, sources, and maturities of “live” oils during the time of entrapment. In the present study, we investigate the bulk fluorescence response of kerogens and macerals from various depositional environments that the objective was to characterize their average fluorescence properties before and during oil generation, with special emphasis on the fluorescence intensity variation as a function of organic species, time, and temperature. The experiments were conducted using the Diamond Anvil Cell (DAC) pyrolysis technique, which enables the measurement of the fluorescence spectra of newly generated “live” oils during maturation experiments. This study aimed to directly address the maturity dependence of fluorescence color variation observed in natural hydrocarbon inclusions, and the effect of source types on the evolutional trend. The fluorescence spectra of oils generated from all studied kerogens exhibit progressive blue-shift of peak wavelengths (λmax) and red/green quotients (I650/I500) upon increasing maturity, suggesting that the fluorescent colors of crude and inclusion oils are both maturity- and source-dependent, and therefore cannot be used as universal maturity indicators.
The initial fluorescence intensities for bulk kerogens (Finitial) under ambient conditions are correlated with their hydrogen index (HI). The Finitial of these kerogens can be correlated with the maximum fluorescence (Fmax) of their generative oils, and may provide some insight into their oil generation potential. Liptinite separated from humic coals exhibits both higher Finitial and Fmax, consistent with their higher oil-generation potential than vitrinite and fusinite (inertinite). Fmax of separated vitrinites show a positive correlation with their maturities below 1.2 %Ro and a negative correlation at higher maturity, implying the decline of their oil generation potentials at high maturity. The present study has demonstrated that the fluorescence of bulk kerogens at elevated temperatures before or during organic transformation can be used to characterize organic matter.
In addition, oils generated from isolated kerogens under confined pyrolysis were characterized by GC-MS for the distributions of aliphatic and aromatic hydrocarbons and biomarkers for studying source dependability of some conventional organic maturity parameters. Normal alkane distribution in oils from different kerogens exhibit distinct preference in carbon number and predominance in specific compounds. The carbon preference index (CPI) and odd-even predominance (OEP) ratios tend to approach to 1 with increasing maturity. The methylphenanthrene ratios (MPR) are suitable for high maturity indication. The methylphenanthrene index (MPI1 and MPI3) from GR kerogen and two marine kerogens show better correlation than terrestrial kerogens. Source dependence of these methylphenanthrene maturity parameters was observed. The MDR ratios (i.e. 4-MDBT/1-MDBT) for two marine kerogens follow oppose trends, suggesting high source-dependence. Two trimethylnaphthalene parameters, TNR-2 and TMNr, exhibit good correlation with maturity for most kerogens, but the MNR, DNR-1, and TNR-1 ratios for GR kerogen are suitable only for indicating maturity higher than 1.0 %Ro. Pr/n-C17 and Ph/n-C18 ratios decrease with increasing maturity but show distinct trends for different kerogens. The pristane/phytane (Pr/Ph) and [(Pr/C17)/(Ph/C18)] ratios in oils from three major kerogen types vary barely with maturity but are discernible in diverse organic types, implying good source indication. The contents of bicyclic sequiterpanes in oils vary with their sources but their relative concentration changes significantly with maturity as a result of neo-formation and/or secondary cracking; the drimane/homodrimane ratio in Green-River oil increases progressively with maturity whereas the eudesmane/drimane ratio in the terrestrial oils decreases with maturity.

並列關鍵字

fluorescence ； aromatic ； biomarker ； source rock

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