Analysis of Microscopic Pore Structure Characteristics and Influencing Factors of Low Permeability Reservoirs‐Taking LD ‐A Oilfield in Bohai Bay Basin as an Example

ABSTRACT

Low‐permeability reservoirs have small pore sizes and difficult fluid flow. Accurately understanding the microscopic pore‐throat structure characteristics of reservoirs is crucial to the development of low‐permeability oilfields. This time, the microscopic pore structure of the low‐permeability reservoir in the LD‐A oilfield of the Bohai Bay Basin was studied by means of scanning electron microscopy, high‐pressure mercury intrusion, nuclear magnetic resonance and X‐ray diffraction. The results show that during the diagenetic process of the reservoir in the study area, some dissolution pores were formed due to material exchanges among feldspar and clay minerals. However, the pore size of the dissolution pores is small and the connectivity is poor and the contribution to the reservoir permeability is weak. The macropores are the important controlling factor of the permeability level in the study area and the mesopores contribute the main movable fluid. The formation of macropores is jointly controlled by compaction, dissolution and cementation. Among them, high quartz content, weak feldspar alteration and low clay mineral content are more conducive to the retention of macropores. The fractal results show that there are obvious differences in the fractal characteristics of pores with different pore sizes and the influence of fractals on reservoir permeability is also different in different pore size ranges. Although the reservoir exhibits the characteristics of double seepage channels, R ₃₀ (the pore throat radius corresponding to the mercury injection saturation of 30%) can still be used as the optimal pore–throat radius in the study area.