Experimental Study on Two-Dimensional Physical Simulation of CO2 Flooding in Daqingzijing Oilfield

As global energy demand continues to grow, the difficulty and cost of extracting oil and gas resources are gradually increasing, making enhanced oil recovery (EOR) one of the key issues in oil and gas field development. CO2 flooding, as an effective tertiary oil recovery technique, has significant advantages in improving recovery rates due to its ability to significantly reduce crude oil viscosity, increase formation energy, and expand the swept volume. However, the effectiveness of CO2 flooding is influenced by various factors, including flooding methods, well patterns, and formation parameters. In this study, a two-dimensional high-temperature and high-pressure simulation device was used to simulate the CO2 flooding process under various flooding methods, including water flooding followed by continuous gas flooding, water–gas alternating flooding, and foam flooding, for two types of injection–production well patterns based on the formation oil parameters of the Hei 125 block in the Daqingzijing Oilfield. The results indicate that during the transition from water flooding to continuous gas flooding, gas breakthrough channels form rapidly, leading to a rapid increase in the produced gas–oil ratio (GOR). Alternatively, alternating injection of gas and liquid can effectively control gas mobility, reduce gas phase permeability, delay gas breakthrough time, and improve oil displacement efficiency. Water–gas alternating flooding forms water–gas slugs, allowing CO2 to enter the tiny pores to contact crude oil, reducing resistance in the pores, and enhancing crude oil displacement efficiency. Although the foam system can expand the fluid sweep range, excessive gas injection can lead to premature gas breakthrough. Furthermore, the type of injection–production well pattern has a significant impact on the overall reservoir recovery for foam system and gas alternating flooding with a 1:1 ratio; adjusting the well pattern can increase the sweep efficiency and improve ultimate recovery. This study reveals the mechanisms by which different flooding methods and well patterns affect the effectiveness of CO2 flooding, providing important theoretical and practical guidance for optimizing flooding strategies and improving oil recovery in oil and gas fields. It is of great significance for promoting the application of CO2 flooding technology in oil and gas field development.