The Secondary Porosity and Permeability Characteristics of Tertiary Strata and Their Origins, Liaodong Bay Basin, China

The petroleum-rich Liaodong Bay basin in Northeast China consists of three depressions (sub-basins) and two uplifts. The Liaozhong depression is the main area of hydrocarbon generation. To date, oil and gas production is mostly from Liaoxi uplift. Early exploration efforts in the deeper portion of the basin indicated that the reservoir quality was poor. However, this study indicates that four distinct zones of secondary porosity and permeability develop in all the depressions and uplifts. The zones of secondary porosity in the depression are relatively deeper than those depths of the same zones in the uplift. Correlations among porosity, permeability, diagenetic stages, evolution of clay minerals, changes in pressure, and thermal maturation indicate the four distinct secondary porosity zones are related to diagenetic evolution, organic matter evolution, clay minerals transformation, overpressure and early hydrocarbon charge. The secondary porosity zones were mainly attributed to the dissolution of the carbonate cement, feldspar and unstable minerals, hydrocarbon generation, and rapid transformation of clay minerals. This result implies that the potential reservoirs with good quality are present in the deeper overpressured portions of the Liaozhong depression.