Pore structure evaluation of low permeability clastic reservoirs based on sedimentation diagenesis: A case study of the Chang 8 reservoirs in the Zhenbei region, Ordos Basin

Sedimentary diagenesis is one of the most significant factors in the development of low permeability sandstone reservoirs due to its important influence on the formation of pore structure. This study takes Group 8 of the Yanchang Formation in the Zhenbei region of the Ordos Basin as the research object. Methods including casting thin-sections, mercury injection, and scanning electron microscopy were used to analyse core and casting thin-sections to examine the sedimentary diagenetic processes, authigenic mineral composition, pore structure, and physical properties of the reservoirs in the study area. The influence of sedimentary diagenesis on the physical properties of the reservoirs was analysed, and the pore structures in the study area were divided into four types. By determining the development mechanism and distribution characteristics of each type of pore structure, the favourable reservoir areas were also predicted. The results showed that type I (large mesopores with medium throats) and type II (mesopores with fine throats) were the favourable pore structures in the research area. These were mainly formed by the rim cementation of chlorite, the dissolution of feldspar and other soluble components, and a weak to mid compaction. Areas with type I and type II pore structures are considered to have a high reservoir quality, with a porosity of between 10% and 25% and a permeability of between 1 mD and 50 mD. These areas are suggested as regions for optimised exploration and development.

Automated summary

This study analyzed the influence of sedimentary diagenesis on the pore structure and physical properties of low permeability sandstone reservoirs, and classified the pore structures in the study area into four types to predict favorable reservoir areas. Areas with type I and type II pore structures were found to have high reservoir quality, with porosity between 10% and 25% and permeability between 1 mD and 50 mD, suggesting them as regions for optimized exploration and development.