Impact of Multi‐Scale Laminae Characteristics on Lacustrine Shale Reservoir Quality: A Case Study From the Second Member of the Kongdian Formation in the Cangdong Sag, Bohai Bay Basin, China

Lamina is the fundamental unit for pore development and hydrocarbon accumulation in lacustrine shale. Taking the shale from the Second Member of the Kongdian Formation in the Cangdong Sag, Bohai Bay Basin, China, as an example, this study integrates technical approaches (X‐ray diffraction, nuclear magnetic resonance, field emission scanning electron microscopy, advanced mineral identification and characterisation system and modular automated processing system) to investigate the relationship between the fabric characteristics at both lamina and lithofacies scale and reservoir quality. The results show that five lamina types are identified in the Ek 2 shale based on inorganic–organic compositions as felsic laminae, mixed laminae, clay laminae, dolomite laminae and organic matter laminae. The storage capacity of shale reservoirs, encompassing pore quantity, size and distribution, is determined by the arrangement patterns of inorganic–organic components within the individual lamina. The rigid framework formed by felsic minerals promotes the development and preservation of interparticle pores and shrinkage organic matter pores, while multiphase crystallisation of dolomite reduces primary intercrystalline pores. Lamina‐scale pore characteristics superimpose on the lithofacies scale through lamination structures, dictating reservoir quality heterogeneity among different lithofacies. The connectivity and seepage condition of shale reservoirs are determined by the differentiation degree and contact pattern of adjacent laminae within the lamination structure. The laminated felsic shale develops a cross‐lamina connected pore–fracture network, with macropores and microfractures being more extensively developed, which is the most promising lithofacies for shale oil exploration and development.