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Enhanced Oil Recovery Secondary Methods

Did you know that primary oil recovery methods only extract 15-20% of the oil in a reservoir? The remaining oil requires advanced techniques known as Enhanced Oil Recovery (EOR) or secondary recovery methods. In this blog, we’ll explore how water injection and gas injection help maximize oil production, especially in ONGC’s onshore and offshore fields.

Enhanced Oil Recovery (EOR) plays a critical role in maximizing oil production from reservoirs. While primary recovery relies on natural reservoir pressure, secondary methods like water flooding and gas injection are used to maintain pressure and extract additional oil. This article explores how EOR using secondary methods works, its techniques, benefits, and challenges in the oil and gas industry.

What Are Secondary Methods in EOR?

Overview of Secondary Recovery Techniques:

Secondary methods in Enhanced Oil Recovery (EOR) are designed to extract additional oil after primary recovery, which relies on the natural pressure of the reservoir. The most common secondary methods include water flooding and gas injection, which help maintain reservoir pressure and push trapped oil toward production wells.

How Secondary Methods Improve Oil Production:

By replenishing reservoir pressure, secondary methods increase the flow of oil, reduce the amount of oil left behind, and can boost overall recovery rates from 20–40% of the original oil in place to significantly higher levels. These techniques also help in sustaining long-term production and improving the economic efficiency of oil fields.

Comparison with Primary Recovery:

Primary Recovery: Relies on natural reservoir pressure or simple mechanical lift to bring oil to the surface. Typically recovers 15–20% of the original oil in place.

Secondary Recovery: Uses injection methods (water or gas) to enhance pressure and extract more oil, often recovering up to 20–50% of the original oil.

Secondary methods serve as a bridge between primary and tertiary recovery, making them a crucial part of modern oil field management.

Why Secondary Oil Recovery?

When natural reservoir pressure drops, primary methods become ineffective. That’s when EOR techniques come into play, helping recover more oil efficiently.

Water Flooding Technique in EOR

What is Water Flooding?

Water flooding is one of the most widely used secondary recovery methods in Enhanced Oil Recovery (EOR). In this technique, water is injected into the reservoir through injection wells to maintain reservoir pressure and push oil toward production wells.

How Water Flooding Works:

1. Injection wells pump water into the oil reservoir.
2. The injected water displaces the oil, driving it toward production wells.
3. This helps increase oil recovery beyond primary methods, which rely solely on natural reservoir pressure.

Benefits of Water Flooding:

1. Boosts oil production and recovery rates.
2. Helps maintain reservoir pressure, preventing premature depletion.
3. Economically cost-effective compared to some tertiary methods.

Challenges of Water Flooding:

1. Reservoir heterogeneity can reduce efficiency.
2. Excess water production may require additional treatment and handling.
3. Needs careful monitoring of injection rates and water quality.

Examples of Successful Water Flooding:

Widely applied in fields in the Middle East, the USA, and India.
Known to increase oil recovery by 10–20% in many reservoirs.

A.  Enhanced Oil Recovery (EOR): Water Injection Well Boosting Oil Production Sustainably

Water Injection Well

Water injection wells are a key secondary oil recovery method, enhancing crude oil extraction by maintaining reservoir pressure and displacing trapped oil. By injecting water into the reservoir, this technique improves sweep efficiency, extending the life of mature oil fields and increasing recovery rates by 20-40%. It’s a cost-effective and environmentally sustainable approach compared to tertiary EOR methods, making it a preferred choice for maximizing output in declining wells. Properly managed waterflooding reduces waste, optimizes resource use, and supports long-term energy production.

How Water Injection Wells Work in Enhanced Oil Recovery (EOR)

Water injection wells boost oil production by flushing trapped oil toward production wells. High-pressure water is pumped into the reservoir, displacing oil and maintaining pressure to prevent decline. Over time, this improves sweep efficiency, recovering additional oil that primary methods leave behind. Advanced monitoring ensures optimal injection rates, preventing water breakthrough and maximizing recovery.

🔹 How It Works:

Water is injected under high pressure (150-250 bar) into the reservoir.

Since water is denser than oil, it pushes the oil towards production wells.

🔹 Key Factors for Success:

✅ Mobility ratio (how easily oil and water flow)

✅ Reservoir geology (rock permeability and structure)

#OilRecovery #WaterFlooding #EOR

🔹 Where It’s Used:

Most oil companies implement this technique in depleted wells to enhance oil recovery, pushing trapped crude toward the production well.

B.  Enhanced Oil Recovery (EOR): Gas Injection Well Maximizing Oil Recovery Efficiently

Gas Injection Well

Gas injection wells are a vital secondary oil recovery method, enhancing production by injecting natural gas, nitrogen, or CO₂ into reservoirs. This technique maintains reservoir pressure and improves oil displacement, pushing trapped crude toward production wells. It’s particularly effective in high-pressure, high-permeability reservoirs, often increasing recovery rates by 20-30%. Gas injection is cost-efficient and environmentally adaptable, especially when using CO₂ for carbon storage benefits.

What is Gas Injection?

Gas injection is a secondary recovery method used in Enhanced Oil Recovery (EOR) to maintain reservoir pressure and improve oil mobility. Various gases such as carbon dioxide (CO₂), natural gas, or nitrogen are injected into the reservoir to displace oil and push it toward production wells.

Types of Gas Injection:

• CO₂ Injection: Reduces oil viscosity and increases flow.
• Natural Gas Injection: Maintains pressure in gas-cap reservoirs.
• Nitrogen Injection: Used when other gases are unavailable; inert and safe for reservoir integrity.

🔹 How It Works:

Gas is injected into the reservoir, where it expands and displaces oil, driving it toward production wells. Depending on the gas type, it may also mix with oil (miscible flooding), reducing viscosity for easier extraction. Advanced monitoring ensures optimal injection rates and sweep efficiency, maximizing recovery while minimizing gas breakthrough.

Natural gas, nitrogen, or CO₂ is injected into the reservoir.

Unlike water injection, gas is usually injected into the gas cap (upper part of the reservoir).

🔹 Benefits:

✔ Maintains reservoir pressure

✔ Helps displace oil towards production wells

🔹 Where It’s Used:

Most oil companies implement this technique in depleted wells to enhance oil recovery, pushing trapped crude toward the production well.

Benefits and Challenges of Secondary EOR Methods

Benefits:

1. Increased Oil Recovery: Secondary methods like water flooding and gas injection can significantly boost oil production, recovering a larger portion of the original oil in place.
2. Extended Reservoir Life: Maintaining reservoir pressure allows longer productive periods for oil fields.
3. Cost-Effective Compared to Tertiary Methods: Secondary methods are generally less expensive than tertiary (chemical or thermal) EOR techniques.
4. Improved Operational Efficiency: Helps optimize production rates and reduce pressure decline.

Challenges:

1. Reservoir Heterogeneity: Variations in rock permeability can reduce efficiency, causing uneven oil displacement.
2. Operational Costs: Continuous injection of water or gas requires monitoring, maintenance, and infrastructure investment.
3. Environmental Concerns: Handling and disposal of produced water or injected gases need proper environmental management.
4. Technical Limitations: Success depends on reservoir type, pressure, and fluid characteristics, requiring careful planning and modeling.

Conclusion

Secondary recovery methods such as water injection and gas injection are critical for maximizing oil production. Companies like ONGC and other major oil producers extensively apply these techniques to enhance oil recovery (EOR), ensuring efficient extraction from depleting reservoirs.

FAQs with Answers: Enhanced Oil Recovery (EOR) Using Secondary Methods

Q1: What is Enhanced Oil Recovery (EOR)?
A: EOR is a set of techniques used to extract additional oil from a reservoir beyond primary recovery, improving production efficiency and extending reservoir life.
Q2: What are secondary methods in EOR?
A: Secondary methods include water flooding and gas injection, which maintain reservoir pressure and push more oil toward production wells.
Q3: How does water flooding work in EOR?
A: Water is injected into the reservoir to displace oil, maintain pressure, and enhance overall recovery rates.
Q4: How does gas injection enhance oil recovery?
A: Gases like CO₂ or natural gas are injected to reduce oil viscosity and increase flow toward production wells.
Q5: What are the benefits of using secondary EOR methods?
A: Secondary methods increase oil recovery rates, optimize reservoir performance, and extend the productive life of oil fields.
Q6: Are there challenges in secondary EOR methods?
A: Yes, challenges include high operational costs, reservoir heterogeneity, and managing water or gas injection efficiency.