辽河西部凹陷页岩纹层结构及其储集空间意义

Laminated texture of shale and its storage space significance in Western Depression, Liaohe Basin

几乎所有的富有机质页岩均不同程度地包含了纹层结构,对应反映了不同的沉积相产物、页岩有机质丰度、生烃能力、储集空间及含气性等特点。按照陆相断陷盆地富有机质页岩的沉积特点并依据有机质分布的连续性差异,将辽河西部凹陷黑色页岩结构划分为连续型、断续型和分散型3种纹层结构。借助岩心观察、薄片分析、扫描电镜等手段,结合统计学研究,对辽河西部凹陷黑色页岩纹层结构进行了研究。沙四段黑色页岩主要形成于半咸水的半深湖相,发育了灰云质型弯曲状连续型纹层和黏土型平直状连续型纹层;沙三段黑色页岩主要为深湖—半深湖相长英质断续型纹层和分散状纹层。连续型碳酸盐混合纹层页岩既可以与化学作用有关,也可以与藻类勃发产生的生物化学作用有关,或者是二者的共同作用。富有机质黏土连续型页岩,主要为气候变化所形成的季节性纹层(生物作用)。断续型纹层通常由黏土纹层有韵律组合,粉砂、黏土则是以平流或层间流的方式季节性输入(机械作用)。页岩纹层形态在很大程度上决定了页岩的生烃能力和生烃特点,进而可能影响储集能力。连续型纹层结构(白云质泥岩)碳酸盐含量高,易发生溶蚀作用,有机质丰度高、生烃能力强,有机孔发育,有机孔—微缝储集空间系统造成含油气性好,且碳酸盐含量与含油气性正相关。断续纹层除发育各种无机孔外,还发育有机孔、沿层理裂缝和矿物解理裂缝,从而导致页岩储集空间发育,页岩含气性条件优越。分散型(块状泥岩)储集空间相对不发育,含气性条件较差。

Almost all organic-rich shale contains stratigraphic structures to varying degrees,reflecting different sedimentary facies,shale organic matter abundance,hydrocarbon generation capacity,reservoir space and gas content.The organic matter (OM) can be divided into three types of occurrence state,namely continuous lamellae,discontinuous lamellae and scattered lamellae,based on the sedimentary characteristics of organic-rich shale in lacustrine rift basins and the heterogeneity of the OM distribution.The black shale stratigraphic structure of the Western Depression of Liaohe Basin was studied using core observation,thin section analysis and scanning electron microscopy,and combined with statistical analysis.The organic-rich shale in the fourth member of Shahejie Formation (Sha-4) was mainly deposited in a semi-deep lake under brackish water conditions,developing carbonate-curved continuous laminae and clay-type flat continuous laminae.The Sha-3 shale,deposited in a freshwater deep-semi-deep lake,is dominantly composed of felsic interlaced laminae and dispersed laminae.The continuous carbonate-mixed lamellar shale can be related to chemical interactions,biochemical interactions caused by algae,or a combination of these two.The organic-rich clay shale is mainly composed of seasonal lamellae formed by climate change.The discontinuous striated layers usually consist of clay lamellae,and silt and clay are seasonally input in the form of advection or inter-layer flow.The shale lamellar morphology largely determines hydrocarbon generation capacity and characteristics,and further may influence reservoir capacity.The continuous lamellae are generally characterized by high carbonate content as well as being prone to dissolution,high TOC abundance,strong hydrocarbon generation ability and abundant organic pores.The organic pore-micro-seam reservoir system would contribute to oil and gas accumulation,and carbonate content is positively correlated with hydrocarbon content.In addition to the development of various inorganic pores,the discontinuous lamellae also develop organic pores,bedding cracks,and mineral cleavage cracks,which lead to the development of shale reservoir space and superior shale gas-bearing conditions.The dispersed lamellae are less prone to dissolution and cracking,so the reservoir space is relatively undeveloped and the gas-bearing conditions are relatively poor.