不同热模拟方式下烃源岩干酪根演化特征红外光谱分析

FTIR analyses of source rock kerogen from different hydrous pyrolysis experiments

烃源岩的生烃过程是在地层孔隙空间内有机质受温度、上覆岩层静岩压力和高地层流体压力(PVT-L共控)等多种作用下的一种复杂的物理化学反应过程。然而目前常用的生烃模拟实验(高压釜加水生烃模拟)大多是在一个低流体压力、无静岩压力、相对较大的生烃空间下进行的,与实际地质情况差异较大。选用南襄盆地泌阳凹陷核三段未熟泥岩分别开展了PVT-L共控和常规高压釜方式加水模拟实验,不同演化阶段干酪根的傅里叶变换红外光谱对比分析表明:(1)伴随着脂族结构裂解、含氧基团脱落及芳香结构缩合,干酪根演化明显呈现出缓慢生油、快速生油和结束生油3个阶段;(2)脂肪度参数IAL、饱芳比参数IL/R和含氧度参数IO表明,同等温度条件下常规高压釜加水模拟脂肪链和含氧基团的热裂解反应更为剧烈,PVT-L共控模拟则相对平缓,380℃时仍伴随有较强的生烃能力;(3)PVT-L共控模拟条件下饱和烃的芳构化程度更低,可能与其限定空间内较高的流体压力有关;(4)含氧度在成熟中期间歇的轻微增大,暗示水对干酪根生烃过程也许有重要的作用。2种不同模拟方式下干酪根红外光谱特征上的差别,暗示其在生烃反应机理上存在较大差异,在热模拟实验研究中要根据研究目的合理选择模拟方式,设置实验条件。

The generation of hydrocarbons occurred through a complex physical and chemical reaction process in finite pore space under lithostatic pressure and fluid pressure（ PVT-L jointly controlled condition）. Most of the hydrous pyrolysis experiments have been carried out with low-pressure and relatively large reaction space due to experimental device limitations. PVT-L jointly controlled experiments and conventional autoclave hydrous pyrolysis experiments have been carried out with immature shale from the Biyang Sag,Nanxiang Basin,and kerogens from the experiments were characterized by FTIR,which expressed four trends：（ 1） Accompanying aliphatic group cracking,oxygen-containing group shedding and aromatic group condensation,the evolution of kerogen experienced three periods including slow oil generation,fast oil generation and finishing oil generation.（ 2） FTIR parameters show more extensive aliphatic group cracking for conventional autoclave hydrous pyrolysis experiments,while there is still relatively strong hydrocarbon generation in the PVT-L jointly controlled experiment.（ 3） The lower aromatization of saturated hydrocarbons in PVT-L jointly controlled experiment may be relevant to higher fluid pressure in a finite space.（ 4） The slight increase of oxygen level implies the role of water in the hydrocarbon generation process. Different evolutionary characters of kerogen reflected the differences of reaction mechanism,which implied that it is important to choose an appropriate experimental mode in practical research.