高过成熟页岩储层演化特征与成因

An insight into the mechanism and evolution of shale reservoir characteristics with over-high maturity

高过成熟是中国南方下古生界海相富有机质页岩储层的重要特征之一,它经历了近乎完整的热演化过程,产出大量油气和有机质孔隙。页岩有机质孔隙实际上包括干酪根孔隙、固体沥青/焦沥青孔隙。依据成岩序列、油气充注、有机质和孔隙的形态特征,识别出固体沥青或焦沥青次生孔隙,并通过典型案例构成的成熟序列,分析影响储层孔隙度与有机质丰度之间关系的主要因素,探究热演化进程中页岩展示出的诸多变化特征与成因,如天然气碳同位素由部分反转进入完全反转区、孔隙表面水润湿—油润湿—水润湿的动态转变、储层电阻率先上升后下降的逆转现象以及岩石各向异性参数的非线性波动,揭示中国南方下古生界页岩气储层可能的演化轨迹,展示不同成熟阶段页岩储层之间的内在变化规律。

Over high maturity is one of the important characteristics of marine organic-rich shale reservoirs from Lower Paleozoic in the Southern China.The organic matter（OM）of gas shale reservoirs almost went through the whole range of thermal evolution.During this wide span,the great amount of hydrocarbon was available and the numerous pores were seen located within OM including kerogen and solid bitumen/pyrobitumen.These nanopores in solid bitumen/pyrobitumen can be identified from SEM image,based on the diagenesis sequence,hydrocarbon charge with the shape of OM and pores.In terms of the maturity process showed by the typical different cases,the main effects on the relationship between reservoir porosity and organic carbon abundance are here interpreted,and the change and mechanism of reservoir properties due to thermal evolution are explored,such as gas carbon isotope from partially rollover zone into completely rollover zone,wettability alteration from water-wet to oil-wet and then water-wet pore surface again,electrical resistivity reversal from increasing stage into decreasing stage,nonlinearity fluctuation of rock anisotropy parameters as well.These indicate the very possible evolution pathway for shale gas reservoirs from Lower Paleozoic in the southern China and the general transformation processes between different shale reservoirs during thermal stages.