What Is Enhanced Oil Recovery?

Enhanced Oil Recovery (EOR) is a set of sophisticated techniques used to extract additional oil from reservoirs after primary and secondary recovery methods have been exhausted.

These advanced processes can significantly increase the amount of oil recovered from mature fields, extending their productive life and maximizing resource utilization.

For industries relying on consistent oil supplies, understanding these technologies is crucial for strategic planning and resource management. This guide will show you precisely how EOR works so that you can understand its impact and economic value.

The Fundamentals of Enhanced Oil Recovery

Enhanced oil recovery is the third stage in the oil extraction process, following primary and secondary recovery methods. During primary recovery, oil naturally flows to the surface due to existing pressure within the reservoir. Secondary recovery involves injecting water or gas to maintain pressure and push additional oil to production wells.

These traditional extraction methods typically recover only 20-40% of a reservoir’s original oil. EOR techniques can boost this recovery rate to an impressive 30-60% or even higher, making previously uneconomical reserves viable again.

EOR works by targeting the oil that remains trapped in the porous rock formations. This trapped oil is often held in place by capillary forces and viscosity issues that prevent it from flowing toward production wells.

The technology essentially modifies the interaction between the oil, the rock formation, and the driving fluid to improve flow dynamics.

The economic viability of EOR projects depends heavily on:

• Oil prices
• Operating costs
• Technological efficiency.

When properly deployed, EOR can breathe new life into declining fields that would otherwise be abandoned.

Three Types of Enhanced Oil Recovery Techniques

Thermal Recovery Methods

Thermal recovery is particularly effective for extracting heavy, viscous oils that resist conventional extraction techniques. This method works by introducing heat to the reservoir, which reduces the oil’s viscosity and allows it to flow more easily toward production wells.

Thermal recovery methods encompass four common techniques:

1. Steam injection: the most common thermal technique, which accounts for a large percentage of EOR production in the United States. Most thermal recovery activities are concentrated in California’s heavy oil fields, where the viscous nature of the oil demands heat-based solutions.
2. Steam flooding: through this method, large volumes of steam are continuously injected into the reservoir. The heat transfers to the oil and surrounding rock, warming the entire formation and maintaining reduced oil viscosity throughout the production zone.
3. Cyclic steam stimulation: sometimes called the “huff and puff” method, this technique involves injecting steam into a well for several weeks, followed by a soaking period. The well is then put back into production, with the process repeated in cycles to maximize recovery.
4. Fire flooding: also known as in-situ combustion, this is a more aggressive thermal approach. It ignites oil within the reservoir itself, creating a combustion front that generates heat and drives oil toward production wells.

Thermal methods require significant energy inputs but can be extremely effective for the right reservoir conditions. The technique is limited primarily to shallow reservoirs with thick, high-porosity formations containing heavy oils.

Gas Injection Techniques

Gas injection is the most widely used EOR method, accounting for approximately 60% of all EOR production in the United States. It involves introducing gases that either expand and push additional oil to the surface or dissolve into the oil to reduce its viscosity.

Carbon dioxide (CO2) is the most common injection gas due to its excellent miscibility properties with crude oil. When CO2 dissolves into oil under pressure, it causes the oil to swell and become less viscous, significantly improving flow rates through the reservoir rock.

Natural gas and nitrogen can be used as alternatives, each with specific applications depending on reservoir characteristics. These gases can be particularly effective in deeper, higher-pressure formations.

The miscible flooding technique occurs when the injected gas fully mixes with the oil, creating a single-phase fluid that flows more easily through the rock formation. This complete mixing eliminates interfacial tension between the oil and gas, maximizing recovery potential.

By contrast, immiscible flooding happens when the injected gas doesn’t fully mix with the oil but still provides pressure support and some viscosity reduction benefits. While less efficient than miscible flooding, it requires less precise pressure management.

Gas injection methods offer excellent recovery rates but demand sophisticated infrastructure for gas handling, compression, and recycling. The technique works best in light to medium oil reservoirs with good permeability characteristics.

Chemical Injection Approaches

Chemical injection methods introduce specialized formulations that alter the relationship between oil, water, and the reservoir rock. Despite accounting for only about 1% of current EOR activities in the United States, these techniques offer promising solutions for specific reservoir challenges.

Here are the most common options:

• Polymer flooding: enhances water flooding operations by adding high-molecular-weight polymers to the injection water. These polymers increase the water’s viscosity, which improves its ability to push oil through the reservoir while reducing fingering effects that can bypass significant oil volumes.
• Surfactant flooding: uses specialized chemicals similar to detergents that reduce the surface tension between oil and water. By decreasing this interfacial tension, the surfactants help release oil that would otherwise remain trapped in the rock pores.
• Alkaline flooding:  involves injecting caustic solutions that react with acidic components in the crude oil. This reaction creates natural surfactants within the reservoir that help mobilize previously immobile oil resources.

Micellar-polymer flooding combines surfactants, polymers, and sometimes co-solvents in a carefully designed chemical package. This comprehensive approach covers multiple recovery challenges simultaneously, though at a significantly higher cost than simpler methods.

Chemical methods require careful formulation based on specific reservoir conditions and oil properties. The factors that must be considered when designing an effective chemical EOR program include:

• Temperature stability
• Rock interactions
• Water sensitivity

Environmental Considerations of Enhanced Oil Recovery

Enhanced oil recovery comes with both environmental challenges and potential benefits. The environmental impacts mainly depend on the specific EOR technique employed and how carefully operations are managed.

Water usage is a major concern, particularly for thermal and chemical methods that can require substantial freshwater resources. Many operations now emphasize produced water recycling and alternative water sources to minimize this impact.

Groundwater contamination risks are also noteworthy, though EOR is regulated under the federal Safe Drinking Water Act’s Underground Injection Control program.

These regulations establish strict requirements for:

• Well construction
• Operation
• Monitoring

Carbon dioxide injection for EOR offers an interesting environmental possibility. When CO2 from industrial sources or direct air capture is used, the process can actually sequester carbon while producing additional oil. This creates a partial offset to the emissions from the ultimately produced petroleum.

The Economic Impact of EOR

From an economic perspective, EOR projects require significant capital investment but can generate substantial returns when oil prices support the additional development costs.

The technology essentially extends the productive life of existing assets, reducing the need for new exploration in environmentally sensitive areas.

The global enhanced oil recovery market continues to expand, with an estimated value of nearly $50 billion in 2024. North America maintains the largest market share, driven by mature field development and supportive government policies.

Technological advancements keep improving the economics of EOR. Innovations like plasma pulse technology and nano-particle enhanced fluids show promise for increasing recovery rates while potentially reducing environmental impacts and operational costs.

Conclusion

By enabling the extraction of 30-60% of the original oil in place (compared to just 20-40% using conventional methods), EOR significantly extends the productive life of mature oil fields.

EOR technologies continue to advance, offering improved efficiency and reduced environmental impact. These innovations ensure that existing oil resources can be developed more completely, reducing the pressure to explore environmentally sensitive regions.

Tyler O'Brien

Tyler is a results-driven marketing professional specializing in the industrial gases and equipment industry, bringing his 10 years of technical expertise and digital marketing acumen to the complex industrial gas B2B environment.