Research on the "multi branch relay" chemical flooding mode for improving oil recovery in high water content and high heterogeneity reservoirs

The issues associated with high water cut and highly heterogeneous reservoirs, such as strong heterogeneity, rapid water cut increase, and the insufficient or difficult mobilization of medium- and low-permeability layers, are addressed. Based on the resistance and residual resistance factors of chemical agents, branched polymers, amphiphilic polymers, and polymer surfactants are classified as high residual resistance, medium resistance, and low resistance systems, respectively. A "multi-branch relay" chemical flooding model is proposed to improve the recovery factor. Through physical and microscopic oil displacement experiments, the dynamic characteristics of the flooding process, as well as the mechanisms of microscopic expansion of sweep efficiency and residual oil mobilization, are analyzed. The physical oil displacement experiments show that the "high residual resistance-medium resistance-low resistance-medium resistance" combination improves the recovery factor by 6.40% compared to continuous polymer flooding. The dynamic characteristics of displacement are observed to have an increasing trend in the production pressure differential, reaching a stable-like state, while the water cut decreases in a "V" shape. Microscopic oil displacement experiments indicate that the "high residual resistance-medium resistance-low resistance- medium resistance" combination improves the sweep efficiency by 33.24% over water flooding. The primary mechanism for mobilizing residual oil involves the segmentation of continuous residual oil patches and the promotion of scattered residual oil reaggregation to form an oil wall. The "multi-branch relay" chemical flooding model effectively addresses the difficulties in initiating and mobilizing oil from medium- and low-permeability layers.