Abstract: Baodao A Gas Field is the first deep water and deep gas field discovered in Baodao Depression. The main gas group of the Baodao A Gas Field is the third member of the Lingshui Formation. The water depth of the gas field varies greatly, the fault system is well developed, the reservoir highly heterogeneous, and the diagenetic phenomena abundant. Affected by the diagenetic transformation, the physical properties of the gas field are poor and the distribution law is complex. Therefore, based on the experimental data of thin section of rock, X-ray diffraction of clay minerals, and oxygen isotope analysis, the reservoir physical property, diagenetic characteristics and quantitative evolution of pores of the low permeability reservoir in the third member of Lingshui Formation in the study area are systematically described. The results show that: mechanical compaction reduces the porosity of the reservoir by 22.0%, which is the main factor of reservoir compaction in the third member of Lingshui Formation in the study area. The porosity of the reservoir is increased by 11.9% by solution and decreased by 13.7% by cementation. The process of pore evolution reveals that compaction is the primary factor contributing to early changes in reservoir physical properties, while mineral dissolution during the middle and late stages of oil and gas charging enhances reservoir space. Subsequently, late-stage carbonate cementation further densifies the reservoir. This research achievement effectively guides the prediction research of favorable reservoirs, provides geological basis for the efficient development of gas fields, and lays a foundation for ensuring the country’s accelerated advancement into the deep sea.

Key words: diagenesis, pore evolution, low permeability reservoir, diagenetic sequence, deepwater gas field