Abstract: Suffered from a long period of weathering, erosion and leaching, karst was widely developed in the Ordovician carbonate rocks in North China. Depending on the morphology and tectonic origin of karst, caves can be divided into dissolved joints, construction joints, corrosion holes, pressure solution seams and the suture lines.The Karst cave, as a type of reservoir, occupies an important position in the oil and gas exploration and development due to its spatial scale. Using some characteristics mentioned in this paper, karst caves are possible to be identified from geological, drilling, and logging records. In accordance with the modern theory of karst formation, caves are developed in a zone 150 meter below the palaeo-weathering crust. The quality of carbonate reservoirs and the migration of oil and gas depend upon the filling degree and connectivity of the caves. Characteristics of logging response to mud-filled and unfilled caves summarized from specific wells are presented in this paper.