Dynamic Evaluation of Sugarcane Drainage Water as a Sustainable Low-Salinity Injection Brine for Enhanced Oil Recovery: Integrated Micromodel Visualization and Coreflooding Study

Technical Summary: Dynamic Evaluation of Sugarcane Drainage Water for Enhanced Oil Recovery

Problem Statement
The study addresses two converging challenges: the increasing scarcity of freshwater resources required for Enhanced Oil Recovery (EOR) and the ecological burden of disposing agricultural wastewater. While Low-Salinity Waterflooding (LSF) is a recognized technique for improving oil recovery, particularly in sandstone reservoirs, most existing research relies on synthetically engineered brines. The potential of naturally occurring, untreated agricultural effluents—specifically sugarcane field drainage water—as a sustainable injection fluid remains largely unexplored. Furthermore, the accumulation of agricultural drainage poses environmental risks, including surface and groundwater degradation. This research investigates whether sugarcane drainage water can serve as a viable, cost-effective, and sustainable alternative to freshwater for EOR applications, specifically targeting the mechanisms of oil mobilization in porous media.

Methodology
The authors employed an integrated approach combining pore-scale visualization and core-scale dynamic testing to evaluate the performance of two distinct sugarcane drainage water samples (Drainage Water 1 and 2) against distilled water as a baseline.

• Materials: Two drainage water samples were collected from sugarcane fields in Khuzestan, Iran, during a period of low fertilizer application to minimize nitrate and phosphate interference. Crude oil with an API gravity of 25.72 was used. Dolomite core plugs (porosity ~25%, permeability ~43–51 mD) and a fabricated glass micromodel with heterogeneous pore structures were utilized.
• Micromodel Experiments: A transparent glass micromodel was used to visualize pore-scale displacement mechanisms. Experiments were conducted at ambient temperature and pressure with injection rates of 0.1, 1, and 10 mL/min. Recovery factors were calculated based on the area of oil displaced after injecting 5 and 20 pore volumes (PV).
• Coreflooding Experiments: Dynamic displacement tests were performed on dolomite core plugs under reservoir-like conditions (80 °C, 600–800 psi overburden pressure). Cores were aged in crude oil for 28 days prior to flooding. Injection was conducted at 0.3 cc/min. Produced fluids were centrifuged to separate oil and water phases for recovery calculation.
• Analysis: The study analyzed the effects of injection rate, fluid chemistry, interfacial tension (IFT), wettability alteration, and emulsion stability.

Key Results
The study demonstrated that sugarcane drainage water significantly outperforms distilled water in oil recovery across both experimental scales.

• Micromodel Performance:

  • Distilled Water: At an injection rate of 10 mL/min and 20 PV, recovery reached 55.78%. Recovery was heavily limited by capillary forces at lower rates (21.73% at 0.1 mL/min).
  • Drainage Water 1: Achieved 72.08% recovery at 10 mL/min (20 PV), showing improvement over distilled water due to natural surface-active components reducing IFT and altering wettability.
  • Drainage Water 2: Demonstrated the highest efficiency, reaching 81.16% recovery at 10 mL/min (20 PV). This sample exhibited superior performance even at low injection rates (38.16% at 0.1 mL/min), attributed to a more effective ionic composition and stronger surface activity.
  • Mechanisms: Visual observations confirmed that drainage waters reduced IFT, altered rock wettability from oil-wet toward neutral/water-wet conditions, and facilitated the formation of stable, finely dispersed emulsions. This reduced capillary trapping and improved microscopic displacement efficiency.

• Coreflooding Performance:

  • Under dynamic conditions (80 °C), distilled water yielded a final recovery of 29%.
  • Drainage Water 1 increased recovery to 43%.
  • Drainage Water 2 achieved the highest core-scale recovery at 45%.
  • The results confirmed that the chemical composition of the drainage waters, specifically their ability to reduce IFT and modify wettability, is the primary driver for enhanced recovery in carbonate-like systems.

• Scale Consistency: While absolute recovery values were higher in the micromodel due to simplified geometry and higher permeability, the performance ranking (Drainage Water 2 > Drainage Water 1 > Distilled Water) remained consistent across both scales.

Key Contributions

1. First Dynamic Evaluation: This study provides the first dynamic evaluation of untreated sugarcane drainage water as an EOR injection brine, moving beyond static compatibility tests to active displacement performance.
2. Sustainable Brine Source: It validates the use of agricultural effluent as a functional injection fluid, offering a dual benefit of reducing freshwater consumption and providing a productive pathway for wastewater management.
3. Mechanistic Insight: The research elucidates that the efficacy of this unconventional water source is driven by natural surface-active components that alter wettability and reduce IFT, mechanisms typically associated with "smart water" or synthetic low-salinity brines.
4. Integrated Methodology: By correlating pore-scale visualization with core-scale dynamic data, the study confirms that the observed recovery mechanisms are robust across different experimental scales.

Significance and Claims
The authors conclude that sugarcane drainage water, particularly Sample 2, serves as a sustainable and cost-effective injection brine for water-based EOR in mature reservoirs. The paper claims that this approach offers a viable alternative to freshwater, capable of significantly improving oil recovery efficiency while addressing environmental challenges associated with agricultural drainage disposal. The findings suggest that utilizing such naturally occurring, low-salinity effluents can contribute to more resilient and environmentally responsible oil production strategies without the need for complex chemical formulation. The study emphasizes that optimizing injection rates and fluid selection based on reservoir characteristics is critical for maximizing these benefits.