Enhanced oil recovery via low-salinity water-alternate-gas injection in carbonate reservoirs: feasibility, optimization, and environmental impact assessment

Project Abstract

In carbonate reservoirs, enhanced oil recovery (EOR) remains a critical challenge, with low-salinity water-alternate-gas (LSWAG) injection emerging as a promising technique to improve sweep efficiency and recoveries while potentially reducing environmental footprint. This study investigates the feasibility, optimization, and environmental impact of LSWAG as a hybrid EOR method, integrating low-salinity water (LSW) pretreatment with gas-assisted displacement to exploit wettability alteration, brine salinity effects, and interfacial tension modifications. A multidisciplinary approach combines core-flood experiments, petrophysical characterization, and reservoir-scale modeling to quantify incremental oil recovery, operational costs, and reservoir performance under realistic carbonate conditions, including varying mineralogy, porosity, temperature, and capillary pressures. Laboratory experiments use meticulously prepared LSW at multiple salinity ranges to evaluate wettability changes, relative permeability hysteresis, and oil/brine/gas interfacial tension under controlled conditions. Phase behavior experiments assess gas miscibility and solubility trends with salinity variations to determine optimal gas types (e.g., CO2, CH4, or hydrocarbon gases) and injection schedules. Core floods simulate sequential LSW and gas cycles, variations in cycle duration, injection rate, and brine salinity to identify synergies that maximize oil displacement while minimizing unfavorable early water breakthrough. Geochemical analyses track mineral dissolution/precipitation and potential scaling risks to anticipate formation damage and equipment corrosion. On the modeling front, a coupled reservoir simulator is calibrated with experimental data to explore sensitivity to salinity, pore-scale wettability, gas compressibility, and reservoir heterogeneity. The study examines different operational strategies, including conventional LSW, gas-assisted LSW, and alternating sequences, to define an optimal protocol that balances incremental oil recovery against water handling, gas utilization, and energy input. Economic optimization incorporates capex/opex, chemical costs, gas procurement, and carbon footprint, performing scenario analyses to determine break-even oil prices and project viability across varying field scales. Environmental assessment encompasses life cycle assessment (LCA) of LSWAG deployment, quantifying emissions, water usage, and potential disposal impacts, along with risk analyses for aquifer integrity and surface ecosystem implications. Preliminary results indicate that carefully tuned LSW cycles can enhance reservoir wettability toward intermediate-wet states, reducing residual oil saturation and improving gas-assisted sweep efficiency in carbonate rocks with high heterogeneity. The integrated framework demonstrates that LSWAG can offer superior oil recovery gains compared to standalone LSW or gas injection under certain salinity regimes, while presenting manageable environmental trade-offs when optimized for water reuse and gas utilization. The findings provide actionable guidelines for field pilots, including key salinity targets, cycle timing, and monitoring metrics, and contribute to a broader understanding of sustainable EOR practices in carbonate reservoirs.

Project Overview

What This Project Is About

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A plain-language overview of the topic and what the project investigates.

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The Problem It Addresses

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What problem or gap this project tackles and why it matters to the field or society.

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Objectives of the Project

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1. Understand what low-salinity water and gas injection do in carbonate rocks.
2. Compare different injection strategies for oil recovery and cost.
3. Evaluate environmental impacts of the chosen methods.
4. Develop a simple optimization plan that balances energy recovery with safety.
5. Summarize practical steps for field implementation.

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What You Will Do Step by Step

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1. Review basic concepts of enhanced oil recovery and carbonate reservoir behavior.
2. Learn what low-salinity water and gas injection mean and how they interact.
3. Set up simple case studies (lab-scale or computer-simulated) to test strategies.
4. Collect data from literature and any available experiments on efficiency and costs.
5. Analyze which methods improve oil recovery the most in carbonate rocks.
6. Assess environmental factors like water use, emissions, and waste handling.
7. Propose an easy-to-follow plan for real-world testing in a field.

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Expected Outcome

Students will gain a clear understanding of how low-salinity water-alternate-gas injection could improve oil recovery in carbonate reservoirs, with a simple framework for evaluating feasibility, optimizing the approach, and assessing environmental impacts. The project should produce a concise set of recommendations for further study or field trials.