Influence of Well Spacing on Polymer Driving in E Reservoir of Daqing Oilfield

The E reservoir in Daqing Oilfield exhibits strong heterogeneity, resulting in inconsistent performance of conventional development methods. Polymer flooding is currently implemented using 106 m and 150 m well patterns. To characterize the influence of well spacing variations on polymer flooding effectiveness and enhance oil recovery, we conducted experiments to evaluate the apparent viscosity, solution concentration, viscoelasticity, plugging resistance, and profile modification performance of polymer solutions at different relative migration distances. Subsequent experiments employing differently scaled intra-layer heterogeneous models investigated polymer flooding’s oil recovery enhancement at various migration distances. Results indicate the following: (1) At identical relative migration distances, polymer systems in shorter sand-packed tubes demonstrate a higher effective migration distance proportion and superior viscoelasticity compared to 30 cm models, enabling more effective remaining oil mobilization and improved microscopic displacement efficiency. (2) The 20 cm sand-packed tube model exhibits enhanced plugging resistance and profile modification capabilities with higher maintained viscosity and concentration retention. Polymer solutions at 20%, 40%, 60%, and 80% migration distances in longer tubes established resistance factors of 30, 15, 7.8, and 3.6, and residual resistance factors of 9.6, 5.6, 2.2, and 1.5, respectively. These solutions effectively migrate to reservoir depths, forming efficient plugs and demonstrating superior deep profile control compared to their longer tube counterparts. (3) Polymer flooding response occurred at 0.194 PV injection in the 40 cm model with a maximum water cut reduction of 36.04%, whereas the 60 cm model required 0.31 PV injection to achieve a response, yielding only a 26.7% maximum water cut reduction. This comparative result demonstrates that smaller well spacing enables faster establishment of effective displacement pressure systems, suppresses high-permeability layer channeling, and significantly improves medium- and low-permeability layer utilization efficiency. (4) Crude oil mobilization in medium- and low-permeability layers is substantially reduced in larger well-spacing models. Collectively, reduced well spacing accelerates polymer flooding response, mitigates reservoir heterogeneity impacts, and extends the operational range of polymer plugging resistance and profile modification capabilities, thereby increasing recovery in heterogeneous reservoirs.