The Huizhou–Lufeng Depression in the Pearl River Mouth Basin is a significant hydrocarbon accumulation zone, where tuffaceous materials exert critical control on the quality of Paleogene Wenchang Formation sandstone reservoirs. However, the role of alteration products derived from different tuffaceous types in governing porosity–permeability evolution remains poorly constrained. To address this issue, an integrated analytical approach was applied, including casting thin section petrography, x‐ray diffraction, electron probe microanalysis, 40 Ar/ 39 Ar dating of authigenic illite, Wood′s metal impregnation, and field emission scanning electron microscopy. The results indicate that the tuffaceous materials are volcaniclastic in origin and can be classified into four genetic types. Reservoir quality is controlled by distinct diagenetic pathways associated with each type. The dissolution of ultrabasic tuff follows a constructive two‐stage process, characterized by early laumontite precipitation and subsequent secondary dissolution. In contrast, dissolution of basic to intermediate tuff leads to the precipitation of quartz and chlorite, whereas alteration of acidic tuff is predominantly destructive, generating abundant kaolinite and illite. Overall, alteration of ultrabasic tuff significantly enhances both porosity and permeability. For basic and intermediate tuff, although dissolution increases porosity, the accompanying cementation of pores by chlorite and quartz reduces pore connectivity, resulting in a decoupling of porosity and permeability. By contrast, the alteration products of acidic tuff tend to clog pore spaces, thereby adversely affecting reservoir quality. This study provides a theoretical framework for understanding Paleogene reservoir evolution and offers practical criteria for identifying favorable exploration targets in the Pearl River Mouth Basin.
Li et al. (Thu,) studied this question.