The benefits of ATBS on retention

📢 Why is polymer retention a critical factor in EOR success?

The benefits of ATBS on retention. Polymer retention is one of the most important parameters in a polymer flooding project. High retention means poor polymer propagation, leading to:
⚠️ Delays in oil bank production
⚠️ Lower viscosity at the flood front, increasing instability
⚠️ Significant additional polymer costs

💡 For example:
At 1000 ppm polymer concentration with a retention of 50 µg/g in sandstone, the delay factor is already 40% of pore volume. Considering $3/kg polymer cost for a 40-acre, 20-ft thick zone, the additional polymer needed to satisfy retention amounts to $1.2 million—a major cost impact.

How to Reduce Polymer Retention?

Since geology is fixed, the only way to decrease retention is to optimize the polymer structure and injection strategy. Here are some potential solutions:

✅ Lower Molecular Weight or Narrow Molecular Weight Distribution

• Reduces hydrodynamic retention at a fixed Interstitial Pore Volume (IPV).
• Drawback: May require higher polymer concentrations to achieve the target viscosity.
• Consideration: An 18 MDa polymer won’t remain as such after perforation—it will degrade to ~15 MDa. Why not start with 15 MDa in the first place? Lab tests using Asymmetric Flow Field-Flow Fractionation (A4F) can help determine the optimal MW distribution.
  

✅ Adjust Total Anionicity

• Modifying polymer charge density affects retention, but selecting the right level is complex.
• Drawback: The possibilities are infinite, requiring extensive testing.

✅ Use a Sacrificial Agent

• Injecting a pre-flush sacrificial polymer can help mitigate retention.
• Drawbacks:
  • Additional cost
  • Difficult to ensure proper zone contact (especially if viscosities differ)
  • Increases operational complexity
  • (Same logic applies to surfactants—a better approach is to slightly overdose HPAM instead.)

✅ Incorporate ATBS (2-Acrylamido-Tertiary-Butyl Sulfonic Acid, a Sulfonated Monomer)

• Benefits of ATBS on retention. ATBS is often called the “aspirin of polymers” because it solves multiple issues:
  ✅ Reduces mechanical degradation
  ✅ Improves thermal and salinity resistance
  ✅ Significantly lowers retention

📊 Case Studies on ATBS Impact:
📌 Rashidi et al. (2011) – Increasing ATBS content reduced retention by 2x to 5x.
📌 GazpromNeft Study – A 5% ATBS polymer had three times lower retention compared to regular HPAM of the same MW and anionicity.

Optimizing Polymer Selection for Cost Efficiency

ATBS-based polymers are more expensive than standard HPAM, but they offer long-term cost savings by reducing polymer retention and improving flood efficiency.

💡 Recommendation: In all polymer flooding studies, include a terpolymer formulation of 70% Acrylamide / 25% Acrylic Acid / 5% ATBS to evaluate retention reduction. A 30% decrease in retention is already a game-changer in EOR economics.

Final Thoughts – Optimizing Retention to Maximize EOR Efficiency

Reducing polymer retention is essential for:
🔹 Faster polymer propagation
🔹 Improved sweep efficiency & flood stability
🔹 Lower operational costs

By choosing the right polymer formulation and injection strategy, operators can optimize performance and achieve greater oil recovery while keeping EOR economics in check.

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