富有机质页岩有机孔隙形成与演化的热模拟实验

Thermal simulation experiment on the formation and evolution of organic pores in organic-rich shale

针对页岩有机孔隙的形成与演化,开展了从未熟—低熟—成熟—高成熟—过成熟全系列的地质条件约束下的成岩成烃演化热模拟实验,利用氩离子抛光-场发射扫描电镜对原始样品和模拟不同演化阶段反应后的样品进行了微观特征分析,研究表明:1未熟、低熟阶段生物化学作用和低温热作用生烃过程中可以形成有机孔隙,其当时较浅的埋深可能有助于有机孔隙的保存;2有机孔隙的形成与演变具有非均质性,成熟度不是控制有机孔隙形成与发育的决定性因素,有机质物理化学结构的差异对有机孔隙的形成与演化具有重要作用;3有机孔隙的发育与滞留油具有明显的相关性,生油阶段生成的有机孔隙,易被热解沥青所占据;4有机质收缩缝/有机质边缘孔可能是页岩气赋存的重要空间,其发育主要受控于在从"化学吸附有机质"向"物理吸附有机质"和"游离有机质"转化时有机质的物理化学结构及演化程度。

To study the formation and evolution of organic pores in shale,the thermal simulation experiments of diagenesis and hydrocarbon generating under the constraint of a whole series of immature-low mature-mature-high mature-overmature geological conditions were conducted.Using Ar-ion milling-field emission scanning electron microscopy to analyze microscopic characteristics of original samples and samples used for simulating reactions of different evolution stages,the research shows：（1）Organic pores can be formed in the process of hydrocarbon generation caused by biochemical action and low temperature heat action in the immature stage and low mature stage,and the shallow buried depth at that time may be conducive to preserving organic pores;（2）The formation and evolution of organic pores is characterized by heterogeneity,and maturity is not the decisive factor controlling the formation and development of organic pores.The difference in physical-chemical structure of organic matter plays an important role in the formation and evolution of organic pores;（3）There is an obvious correlation between the development of organic pores and retention oil.Organic pores generated in the stage of hydrocarbon generation are easy to be occupied by heat decomposed pitch;（4）Constricted fissure/marginal pore of organic matter may be an important space for shale gas occurrence,whose development is mainly controlled by the physical-chemical structure and evolution degree of organic matter when it is transformed from chemisorption-type organic to physical absorption-type organic and free organic.