Abstract:

Cluster sampling was performed in the vicinity of the sequence boundary within deltaic sedimentary system and a detailed analysis of lithological and mineral composition was carried out on the samples gathered. The results reveal the diagenetic reaction patterns near the boundary. The constraints of the sequence boundary over diagenetic reaction are reflected in the following aspects.First，sequence boundary indicates a relative fall in lacustrine level，which led to flush and leach of meteoric waters and facilitate the kaolinitization of siliciclastic grains（mainly unstable feldspar），thus causing a higher kaolinite content in the bulk composition of the under-lying formation of the boundary. Secondly，the boundary means a relative longer residence time of the sediments，which increasing the content of carbonate cement in reservoirs under the boundary. Finally，the boundary is usually accompanied by a decrease in accommodation space，causing a large amount of fineˉgrained sediments being flushed and eroded by overlaying coarseˉgrained sediments and then leached into the underlying formation. With the increase of burial depth，these filling materials become pseudo matrix under compaction and reflected as a signal of higher content of claymatrix under the boundary. These diagenetic alterations have an obvious impact on reservoir quality. The kaolinite cement，for instance，has a positive effect upon the porosity of reservoirs; while clay matrix and carbonate cement，on the contrary，exert a negative effect upon reservoir porosity.

Key words: pseudo matrix, kaolinite, carbonate cement, physical property of reservoirs, sequence boundary, diagenesis, Huim in Sag, Jiyang Depression