Hangzhou Institute of Petroleum Geology, PetroChina Exploration and Development Research Institute, Hangzhou 310023, Zhejiang, China

Abstract：Devonian reef is developed in the Guizhong depression, and drilling data of well GZ1 support the opinion that high quality biolithite and dolomite reservoirs do exist in the Guizhong depression. Outcrops, micrographs and scanning electronic microscope analyses show that reservoir space is composed of pores , fissures and solution hollows. The interstices include such types as intragranular corroded hollows, frame pores, inter granular pores, corroded hollows and corroded hollows associated with stylolite, with the intercrystalline pores, intercrystalline corroded hollows and corroded pores as well as hollow fissures controlled by nonfabric materials being the main types. It is suggested that the reservoir types can be classified into fissure type, fissure pore type and pore type. The depositional environment, diagenesis and tectoclase controlled the development of the beneficial reservoir. Nowadays reservoir space is mainly made up of burial emposieus and remaining pores, fissures and solution hollows. A study of diagenesis and geochemistry indicates that the porosity evolution was related to the oil accumulation, and that two stages of processes of oil reservoir formation might have occurred. The solid bitumen (or destruction) of the reservoir was related to thermal evolution of the oil due to the subsidence. It is therefore held that the exploration should be mainly concentrated on the oil-cracked gas, with the attention paid to the study of reservation conditions of the rocks.