Abstract:   Baiyun sag in the Pearl River Mouth basin is an important target for deepwater exploration, which has a highly variable geothermal gradient. The geothermal gradient of a single well is as high as 66.4 ℃/km. The high geothermal field has an important control effect on the diagenesis of the reservoir, affecting the evolution of pores and the changing trend of the relationship between porosity and permeability. However, the influence mechanism of geothermal gradient on reservoir quality under the background of high geothermal gradient is still unclear, which seriously restricts the further exploration deployment.By analyzing  rock samples from  Eocene to the Early Miocene in the study area, the relationship among genthermal field, formation temperature, petrological composition and reservoir evolution in deepwater area is comprehensively analyzed by means of comparative study.   The permeability of  Zhujiang Formation and Zhuhai Formation decreases rapidly with the increase of  formation temperature and burial depth. When the formation  temperature exceeds 140 ℃, the permeability is usually less than 1 mD. The sandstone pores are mainly secondary pores with carbonate cement and authigenic clay minerals inside. However,  Enping Formation exhibits different characteristics, maintaining a high permeability up to 200 mD, even with a rapid decrease in porosity. The sandstone of  Enping Formation is a set of coarse-grained sandstone, mainly composed of quartz, with preserved primary pores, good pore structure, less intergranular filling with cement, and good porosity-permeability relationship. It could be concluded that the decreasing rate of porosity and permeability in the reservoir was controlled by the geothermal field as well as the primary composition of sandstone.

Key words: reservoir, diagenesis, high geothermal field, reservoir pore evolution, Baiyun sag, Pearl River Mouth basin