影响海相烃源岩热解生烃过程的地质条件

Key Geological Conditions Affecting Pyrolysis Experiments of Marine Source Rocks for Hydrocarbon Generation

热解生烃实验是研究油气生成机理与定量评价烃源岩生烃潜力的重要方法.烃源岩热解生烃模拟结果不仅与温度、压力和时间等因素有关,而且与地层孔隙水及压实成岩作用等地质因素密切相关.采用高压流体和高压釜（低压水蒸气）两种生烃热模拟方法对低成熟海相二叠统大隆组（P2d）黑色泥岩进行了热解生烃实验模拟.对比分析两组实验结果表明地层孔隙热解实验有利于液态油的生成,不利于液态油向气态烃的转化,并极大地提高了干酪根的生油气潜力,显示了高压液态水、流体压力和孔隙空间等地质因素对烃源岩中有机质热成熟生烃反应的重要影响.这种影响可能与高压液态水的近临界特性有关,近临界特性地层水的参与改变了干酪根热力生烃反应的物理化学行为.推断在实际地质温压（100-200℃,30-120MPa）条件下,烃源岩孔隙中的地层水是一种相对低温高压液态水,具有水的近临界物理化学特性,因此高压流体生烃热模拟实验与实际地层情况更为接近,能更有效地评价烃源岩生烃潜力。

Hydrocarbon generation simulation experiment（pyrolysis）is important for studying petroleum generation mechanisms and quantitatively estimating hydrocarbon generation potential of source rocks.The simulation experiment results not only depend on the temperature,pressure and duration,but also on the pore fluid,source rock compaction.In this paper,marine black mudstone with low maturity from the Permian Dalong Formation（P2d）is used for hydrocarbon generation simulations with two types of high-pressure liquid water and low-pressure water steam.The results show that the high-pressure liquid water can increase the organic matter petroleum generation potential greatly,enhancing oil generation and retarding the transformation from oil to gas,suggesting important influence of geological factors such as high-pressure liquid water,fluid pressure and pore space on the hydrocarbon generation of the source rocks.The increase of the petroleum generation potential is due to the fact that the physicochemistry reaction of the kerogen is greatly enhanced at the presence of the near-critical properties water.It is concluded that the water in the pore space of the source rocks is of the high-pressure and low-temperature liquid water in the subsurface temperature（100-200℃）and pressure（30-120MPa）conditions,which has the properties of nearcritical water.Therefore,the hydrocarbon generation simulation experiment（pyrolysis）with high-pressure liquid water ismore close to the actual geological conditions than that of the low pressure water steam and could be used to estimate hydrocarbon generation potential of source rock more effectively.