Shale lithofacies and reservoir space of the Wufeng–Longmaxi Formation, Sichuan Basin, China

Based on observation of the outcrops and cores of the Late Ordovician to the Early Silurian Wufeng-Longmaxi shale, developed in the deep water shelf environment, in the southeast of the Sichuan Basin, the mineralogical features, lithofacies characteristics and reservoir space types were studied and the factors affecting reservoir capacity were analyzed by observation of eletron microscope and analysis of mineral content. The mineral composition is dominantly clastic quartz and clay minerals, with feldspar, calcite, dolomite, pyrite and so on. Five lithofacies, i.e. carbonaceous shale, siliceous shale, silty shale, calcareous shale and ordinary shale, were identified in the Wufeng–Longmaxi shale. Seven types of reservoir space, including structural tension fracture, structural shear fracture, interlayer lamellation fracture, pyrite pore, the inter-crystal micro-pore and micro-crack in clay mineral, the edge micro-crack around quartz grains and organic matter pore, were found in the Wufeng–Longmaxi shale. The development of reservoir space is strongly controlled by the mineral composition, lithofacies, organic carbon content, organic matter maturity and diagenesis.