Songkan formation cores of Anye-1 well and outcrops, together with geochemistry, petrology and reservoir of Songkan formation shales, show dark gray thin-layered calcic shale interbeded with granular argillaceous limestone, with a rising lime and falling siltstone upwards. The TOC of Songkan formation in Anye-1 well district is generally lower than 1.0%, most at 0.1%. Its organic matters of calcic sandy mudstone are type II1, implying a higher thermal evolution with maturity at 2.75%-2.92%, average at 2.85%. The highly-interbeded mudstone and limestone can form a sealing layer in preserving shale gas. The horizontal cracks develop in mudstone, not in limestone, which is closely related to higher gas content indicated by the on-site tests. Although the organic carbon is not high in its mudstone and limestone, the gas has been enriched due to the sealing interbeded limestone.