Multiple Sets of Unconformity Migration Capacity and Their Influence on Hydrocarbon Accumulation in the Bozhong Area of the Bohai Bay Basin

Abstract

The Bohai Bay Basin is one of China's largest basins in terms of discovered hydrocarbon reserves. In this basin, unconformities serve as key pathways for the lateral migration of hydrocarbons, with the T8, T5 and T2 unconformities being the main ones developed here. Studying how these three unconformities differ in migration capacity is therefore essential for understanding hydrocarbon accumulation. By using logging data, along with measurements of porosity, permeability and sedimentary facies distribution, we analysed and compared the structures, physical properties and continuity of these unconformities. Based on this analysis, we linked hydrocarbon reserves per unit area to migration probability and developed a model for migration range. The results show that: (1) Although the T8 unconformity has poorer porosity and permeability compared to T5, it provides better continuity for migration channels, making T8 the main pathway in depressions, while T5 is more discontinuous and thus likely to form lithologic reservoirs in these areas. (2) T8 and T5 overlap gradually along the uplift belts, where both the porosity-permeability and thickness of these unconformities improve, and T2 has both good continuity and physical properties, facilitating lateral migration on the uplift belts. (3) Compared with other unconformities, T2 is the primary migration pathway above the uplift areas.