The main oil-bearing formation of Area 4 of Tahe oilfield is in Yingshan Group of Ordovician consisted ofthick pure limestone. The types of the pore space contain the pore, fissure, cave as well as fracture formed bysolution collapse. The primary porosity and tectonic fracture are of poor growth. Therefore, the formation growthis mainly controlled by hydraulic units of the palaeo-karst.There are three palaeo-hydraulic zones:vadose zone(including infiltration sub-zone and percolation sub-zone), phreatic zone and tranquil zone. They are identified byretrieving the palaeo-geographical karst environment. The pore space of the infiltration zone is mainly soutionfissures, small solution cavities and solution pores. The growth and lateral connection of the formation arefavorable. The reservoir/formation ratio is 0. 54. The pore space of the phreatic zone developed large sise cavitiesand fractures related to cave collapse. The height of the cavity can reach 71m. The fractures by collapse have ainfluencing range