Chlorite characterization and diagenetic evolution as primary controls on Zhuhai Formation sandstone reservoir quality in Zhu-III sag, Pearl River Mouth Basin, south China sea

Abstract

Zhu-Ⅲ sag in the Pearl River Mouth Basin is rich in hydrocarbon resources. The Oligocene Zhuhai Formation is a key exploration horizon in Zhu-Ⅲ sag. However, the exploration results show that the reservoir is deeply buried, the diagenesis is complex and the reservoir heterogeneity is strong. Therefore, looking for high-quality reservoirs, which are the zones with relatively high porosity and permeability, is a key point of resource exploration. Based on the previous research results, this study analyzed the reservoir characteristics and diagenesis characteristics, established the pore evolution model of the study area, and defined the main controlling factors of reservoir development and used core observation, thin section, scanning electron microscope, X-ray diffraction and so on. The research shows that compaction is the main reason for the reservoir densification of Zhuhai Formation. Chlorite in Zhu-III sag consists of two occurrence states and characteristics. These two kinds of chlorite have a great influence on reservoir quality in three key zones. Pore-lining chlorite can effectively improve the reservoir quality. Another is chlorite cement which can destroy the pore structure. Meanwhile, fluid-controlled carbonate cement also has an obvious effect on the reservoirs in key zones. Fluid in early stage leads to the formation of carbonate cement and that in late stage leads to the dissolution of carbonate cement. In general, we clarify the diagenesis and pore evolution in key zones in Zhu-Ⅲ sag and its reservoir is mainly affected by compaction, dissolution, chlorite and hydrocarbon charging. This study of reservoir diagenetic evolution process and pore characteristics is crucial and helpful in the exploration and development of reservoir in Pearl River Mouth Basin and other basin.