Mechanistic Study on the Decrease in Injectivity during Salt-Resistant Polymer Flooding.

Area of Science:

• Petroleum Engineering
• Enhanced Oil Recovery
• Polymer Flooding

Background:

• Polymer flooding enhances oil recovery by improving sweep efficiency but can cause reservoir damage through permeability reduction and pore plugging.
• Proper selection of polymer type and concentration is crucial to mitigate reservoir damage during oilfield development.
• Salt-resistant polymers (SRPs) are used in specific oilfield applications, necessitating an understanding of their reservoir interaction.

Purpose of the Study:

• To determine the plugging extent and injection limits of salt-resistant polymers (SRPs) in the Daqing Oilfield.
• To provide guidelines for selecting appropriate SRP molecular mass and concentration based on reservoir conditions.

Main Methods:

• Conducted oil displacement experiments using reservoir fluid and core samples.
• Performed dynamic and static adsorption experiments to quantify polymer-reservoir interactions.
• Utilized Scanning Electron Microscopy (SEM) for pore structure analysis.

Main Results:

• Static adsorption of medium-molecular SRP reached equilibrium in 36 hours with a saturated adsorption capacity of 3.56 mg/g (2-5 times dynamic adsorption).
• For medium-molecular SRP (7 million molecular mass), the lower core permeability limit for injection was 20-40 mD.
• SRP concentrations exceeding 900 mg/L were found to be detrimental in cores with permeability below 100 mD, with reduced oil displacement capacity and critical water permeability decrease.

Conclusions:

• SRP adsorption and sand-carrying retention significantly reduce reservoir water permeability, indicating potential for pore plugging.
• The study establishes critical injection limits for SRP concentration and molecular mass relative to reservoir permeability.
• Findings offer valuable insights for optimizing SRP flooding strategies in the Daqing Oilfield under varying geological conditions.