Evolution of diagenetic fluids in the deeply buried, upper Ediacaran Dengying Formation, Central Sichuan Basin, China

Deeply buried Precambrian carbonate reservoirs host economic petroleum reserves. The upper Ediacaran Dengying Formation (maximum burial depth >8 km) is predominantly composed of dolostone with porosity ranging from 2 to 4%, and minor limestone with a porosity of 13C values, while their δ18O values gradually decrease during the paragenetic sequence. Multiphase dolomitisation led to the increase in Ca/Mg ratios of formation water and reservoir performance. This study is significant for those concerned with the deeply buried dolostone reservoirs. KEY POINTSMicrobialites and five types of dolomite cements have different REY patterns.Co-precipitation of fluorite led to the superchondritic Y/Ho ratios of dolomite.Dolomite and calcite grains show micro-scale geochemical variations.This dolostone reservoir underwent multiphase fluids, including meteoric water, seawater and hydrothermal fluid. Microbialites and five types of dolomite cements have different REY patterns. Co-precipitation of fluorite led to the superchondritic Y/Ho ratios of dolomite. Dolomite and calcite grains show micro-scale geochemical variations. This dolostone reservoir underwent multiphase fluids, including meteoric water, seawater and hydrothermal fluid.