Classification and characteristics of karst reservoirs in China and related theories

Karst reservoirs are distributed widely in China, for which integrated geological, logging, testing, and seismic identification marks can be made and their ages can be determined using unconformity surfaces, the lithologic features, and paleobiology of cavern clastic fillings and element geochemistry. The karst reservoirs can be classified as buried hill karst, reef-bank karst, internal karst, bedding deep-underflow karst, vertical deep-infiltration karst, and hydrothermal fluid karst. The first three belong to base-level karsts, controlled by different-order sequence interfaces; the last three belong to nonbase-level karsts, which are controlled by tectonics and fracture. The division of karst facies should take full account of the internal relation of the base-level karsts and the nonbase-level karsts, the existence of deep-turbulent flow zones and the genetic type of karsts. There are many types of corrosion fluid in carbonate rocks in petroleum basins. It is important for the reservoir evaluation and prediction to reconstruct them and to analyze the genetic mechanics of the karst pore-cave-fracture and large-scale cave. As for the controlling factors for the karst development, the study of zonal exogenic forces should be enhanced while the study of azonal endogenic forces is emphasized.