摘要
对塔里木盆地侏罗系煤岩在不同介质下的热模拟实验和正构烷烃系列色质测试分析结果表明，在400℃前后煤岩成烃机理不同。结合对峰型、∑C21-／∑C22＋值、OEP指数和Pr／Ph值等地球化学参数的研究，指出了不同热演化阶段的成烃机理：在低温阶段（〈350℃）煤岩主要是裂隙、晶格间吸附烃和结构边缘烃的排出；在350～400℃之间，脱甲基及链断裂效应使得煤岩排烃进入高峰期；在高演化阶段（≥450℃），大量内部结构烃发生断裂重排，550℃以上温度达到第二个热降解高峰，产出烃发生脱甲基、链断裂和开环效应。模拟实验还表明，OEP指数变化较大，其每次变化都伴随一次生烃高峰；Pr／Ph值随着热演化程度呈降低趋势；有水、伊利石和蒙脱石存在时，会改变煤岩在热演化过程中高碳数烃的热降解速率，有利于液态烃的形成。
The Jurassic coals from Tarim basin with different minerals and water were subjected to closed system pyrolysis ,in sealed steel tubes, under isothermal temperature conditions, ranging from 250 to 550℃ at temperature intervals of 50℃ （pyrolysis time 72 hours）. The distribution of n alkanes extracted from pyrolysate products illustrates the difference of hydrocarbon origins before and after 400℃. Together with these geochemical features, such as peak types,∑C21-/∑C22＋,OEP and Pr/Ph ratios, the results are re ferred as follows： at low stress satges（〈350 ℃）, soluble organic matter from coal samples is derived from trapping of hydrocarbon in lattices and fractures of coals and marginal portions of the coal structure,then, demethy function and cleavage of long chain occur with the onset of peak generation of hydrocarbons at the range of 350～400℃, aromatizalion, condensation of hydrocarbon fractions and cleavage and rearrange ment of coal structures happens at high thermal stress（≥450 ℃）, finally the formed hydrocarbon fractions undergo the thermal process of demethy, chain cleavage and ring open, corresponding to the temperature of 550 ℃ or more. The OEP will change greatly when hydrocarbon forming peak appearing. The Pr/Ph ra tios decrease with the thermal simulation temperature increasing. As a whole, if water and clay（montmorillonite or illite） exist in coal forming hydrocarbon, the degraded ratios of high number hydrocarbons to low molecular hydrocarbons will be changed during the thermal stress and water and clay（montmorillonite or illite） is in favor of forming hydrocarbon from coal rocks.
出处
《天然气地球科学》
EI
CAS
CSCD
2006年第3期313-318,共6页
Natural Gas Geoscience
