Abstract
Addressing the challenge of significant physical property variations in heterogeneous reservoirs, where conventional water flooding easily induces channeling, the current research focus lies in utilizing CO(2)-water alternating gas (CO(2)-WAG) or a CO(2)-water/polymer composite alternating flooding to control fluid mobility and reduce gas channeling, thereby enhancing oil displacement efficiency. While existing studies primarily concentrate on single-reservoir types (e.g., purely high permeability or purely low permeability), this research employs core samples from the TX block (predominantly medium-high permeability) and CS block (predominantly medium-low permeability) of a specific oilfield. By adjustment of the size of periodic slugs, parallel long-core flooding experiments were sequentially conducted for CO(2)-WAG and CO(2)-water/polymer alternating flooding. Nuclear magnetic resonance (NMR) technology was integrated to quantitatively characterize the oil displacement effectiveness of the composite CO(2)-water/polymer flooding under different heterogeneous physical properties and microscopic pore characteristics. The experimental results indicate that during CO(2)-WAG flooding, the core recovery factor from the TX block (medium-high perm) was higher than that from the CS block (medium-low perm). During CO(2)-water/polymer composite alternating flooding, the core recovery factor from the CS block (medium-low perm) exceeded that from the TX block (medium-high perm). CO(2)-WAG effectively mitigates gas channeling in medium-high permeability heterogeneous reservoirs, while CO(2)-water/polymer alternating flooding effectively reduces gas channeling in medium-low permeability heterogeneous reservoirs and enlarges the microscopic swept volume. The conclusions of this study provide a theoretical basis and a practical reference for the differentiated development of similar reservoirs.