Waterflooding remains the primary development method for heavy oil reservoirs in the Bohai Bay unconsolidated sandstone reservoir. These reservoirs, characterized by low strength and poor cementation, are prone to blockage and formation damage during production. Additionally, large vertical permeability contrasts cause uneven water injection across layers. With the advancement of frac and pack technology, significant progress has been made in production wells for improving sand control, unblocking and enhancing productivity. However, its application in injection wells, which also face blockage and uneven water injection, has received limited attention, and the understanding of frac and pack’s impact on fluid migration in reservoirs remains incomplete. Two mechanistic models for single-layer and multi-layer production are established in this study, using numerical simulation to investigate the impact of frac and pack completions on oil and water migration in water injection wells. For single-layer production, water injection wells with varying degrees of formation damage in reservoirs of different permeability are simulated with and without fracturing. For multi-layer commingled production, simulations are conducted for injection wells under undamaged, mildly damaged, and severely damaged conditions, examining scenarios where the low-permeability layer, high-permeability layer, and both layers are fractured. Results indicate that fracturing through the damage zone effectively unblocks the reservoir and increases productivity. In cases of minimal damage for formation, fracturing the low-permeability layer of the injection well balances injection and improves production. When severe damage occurs, fracturing both the high and low-permeability layers enhances unblocking and production performance.