Reservoir pore structure is intimately linked to seepage characteristics; thus, determining its spatial variations is essential for formulating precise development schemes and remaining oil recovery strategies. Although the second member of the Shahejie Formation (Es2) reservoir in the central-eastern Jizhong Depression generally possesses favorable macroscopic physical properties, discrepancies exist in dynamic development performance and remaining oil distribution across different regions. To clarify the influence of pore structure on seepage behavior, this study investigates the Es2 reservoir in the Wen’an and Wuqiang areas of the Jizhong Depression, Bohai Bay Basin, utilizing integrated analytical methods including casting thin sections, scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), relative permeability tests, and microscopic visualized percolation experiments. The results demonstrate that the Wen’an area is dominated by primary intergranular pores with a bimodal throat distribution. Despite a high areal porosity (21.6%), its fine throats (3.87 μm) and severe heterogeneity (sorting coefficient: 16.20) lead to poor connectivity (mercury withdrawal efficiency: 11.29%), resulting in a finger-like water drive, a narrow two-phase co-seepage zone (30.48%), and a lower ultimate displacement efficiency (50.64%). In contrast, the Wuqiang area features dissolved-intergranular pores with a unimodal throat distribution. Benefiting from larger throats (7.75 μm) and lower heterogeneity (sorting coefficient: 4.32), it exhibits superior connectivity (mercury withdrawal efficiency: 31.57%), uniform displacement, a wider co-seepage zone (40.72%), and a higher ultimate efficiency (59.34%). Given the lower waterflooding efficiency in the Wen’an area, subsequent gas displacement experiments following waterflooding demonstrated an overall recovery increment of 25.83%. Based on the disparities in pore structures and seepage characteristics between the two areas, it is recommended that the Wuqiang area should continue utilizing conventional waterflooding, while the Wen’an area should consider gas displacement after waterflooding.
Xiang et al. (Tue,) studied this question.