Upstream Oil and Gas

Enhanced Oil Recovery (EOR) Techniques and Helpful Technology

April 13, 2022 Welcome

What is enhanced oil recovery, and how are EOR methods utilized in the oil and gas industry? This article will discuss the various oil and gas recovery methods, focusing mainly on tertiary or enhanced oil recovery (EOR) operations.

Types of Oil Recovery

Oil recovery in hydrocarbon production is a series of efforts to obtain as much oil & gas as possible from a hydrocarbon-bearing reservoir. Typically, the production rate varies over the lifecycle of a well. Therefore, the formation will require additional stimulation to ensure that production volumes remain at sustainable levels for as long as possible.

For optimal oil recovery, various techniques and technologies are employed across several phases depending on the age of the well, formation characteristics, and the cost of operation.

Now, let’s explore the different oil recovery techniques. Oil recovery efforts fall into three broad categories – primary, secondary, and tertiary oil recovery (also known as enhanced oil recovery). Let’s look at these three in closer detail:

1. Primary Oil Recovery

Primary recovery is employed during the initial phase of oil production. For conventional oil and gas, it begins immediately after drilling operations have been concluded. Then, a Christmas tree (oil well) is installed at the wellhead. In primary recovery, oil production is chiefly due to the natural formation pressure of the reservoir and basic pumping operations via the production casing. However, primary oil recovery techniques recover only about 30% of OIIP.

2. Secondary Oil Recovery

Secondary recovery follows primary recovery, typically due to a decline in the natural formation pressure of the reservoir. The operator may inject gas or steam flooding into the reservoir through an injection well to force more oil toward the production casing. Secondary oil recovery methods can help operators recover up to 60% of OIIP.

3. Tertiary Oil Recovery

Tertiary oil recovery techniques are employed extensively in unconventional oil and gas plays across the US and brownfields, where they help operators recover up to 75% of the oil initially in place (OIIP). Consequently, this ramps up existing production by up to 300%!

What Is EOR?

Enhanced oil recovery (EOR) is the process of artificially stimulating a reservoir to recover more oil after secondary recovery techniques have become unable to sustain desired production volumes. Additionally, EOR is usually employed when the oil left in the reservoir is trapped in hard-to-reach (low-permeability) sections with poor oil-water contact or irregular fault lines.

Enhanced Oil Recovery vs Fracking

Although they are similar processes, there are a few notable differences between EOR and fracking.

EOR is a process that increases the amount of crude oil that can be extracted from an oil field. It is usually done by injecting water or gas into a reservoir to increase pressure and force the crude out of the rock. Fracking is a process that involves drilling down into the earth before a high-pressure water mixture is directed at the rock to create cracks in it. These cracks allow natural gas or petroleum to escape, making them easier to extract.

In other words, fracking forces open new fissures in the rock, while enhanced oil recovery “scrubs” existing channels.

How Does Enhanced Oil Recovery Work? Top 3 EOR Methods

Enhanced recovery methods for oil and natural gas are employed after secondary recovery techniques are insufficient to sustain profitable production. This is due mainly to a severe decline in reservoir pressure or unconventional oil and gas plays such as shale or tight sandstone.

The major enhanced oil recovery processes and operations include chemical injection, steam injection, and gas injection. These methods typically require non-standard enhanced oil recovery technology.

1. Gas Injection

Gas injection as an EOR method uses nitrogen gas (N₂) or Carbon dioxide (CO₂) for the miscible displacement of crude in unconventional reservoirs our mature wells. The principle for recovery is that when the gas dissolves in the oil, it reduces its viscosity, improving mobility. According to the US Department of Energy, gas injection techniques account for nearly 60% of EOR production in the United States.

To successfully carry out a gas injection, CO₂ pumps into the formation via injection wells. At high downhole pressures, the gas forms a miscible zone that mops up stranded oil and forces it towards the production casing of the target well. Gas injection is often alternated with water injection using a water injection pump system to further improve sweep efficiency.

Due to growing concerns about the impact of CO₂(a known greenhouse gas) on global climate change, operators may opt to use high-purity nitrogen gas. Typically, N₂is also favorable over CO₂ because it has relatively inert properties that prevent downhole combustion. In addition, N₂ can be generated cost-effectively from atmospheric air using a nitrogen generator skid.

2. Steam Injection

Steam injection enhanced oil recovery (also called thermal recovery or steam flooding) refers to the injection of water vapor at high pressure and temperature into a well to mop up stranded oil from the reservoir following a decline in the formation pressure.

To carry out steam injection, an operator drills one or more ‘injection’ wells close to the well for stimulation. Next, steam is introduced into the formation via the injection well(s). When it contacts the oil, it lowers its viscosity and increases its kinetic energy, improving mobility toward the production casing. Steam injection is particularly useful for oil recovery in heavy oil reservoirs. Additionally, steam injection techniques account for over 40% of EOR production in the United States, primarily in California.

3. Chemical Injection

In chemical injection, long-chain polymers are injected into a well via a chemical injection skid to free up oil and gas molecules from remote sections of the reservoir. Chemical injection can be done alongside waterflooding. This effectively improves the recovery factor by increasing the efficacy of the surfactants for improved mobility of hydrocarbons.

The polymers utilized in this EOR process can be alkaline or micellar substances which enhance the flow of crude (sweep efficiency) by reducing the interfacial tension between the hydrocarbon molecules and water present in the reservoir.

C0₂ Injection

In addition to these three enhanced oil recovery types, CO₂injection is also a valuable method. CO₂ pumps and injection pumps are used in the carbon sequestration (i.e. C0₂ sequestration) process. This injection method is crucial for handling the corrosion, scaling, and potential higher temperatures that occur in re-injection. AP-610 pumps are particularly effective when it comes to CO₂ pumping/injection and there is a full line of pumps available to meet your Carbon Capture, Utilization, and Storage (CCUS) needs. Here are a few examples:

Process pumps
In-line pumps
Vertical pumps
Single-stage double pumps
Split-case pumps
Barrel pumps
Packaged systems and more

Check out this article to learn how Co₂ pumping helps with natural gas processing.

Use IFS Modular Process Skids to Support Your EOR Technology

IFS is a best-in-class manufacturer of process equipment for the oilfield industry. We provide a range of modular process skids to support your EOR operations, with rugged durability suitable for the most challenging oil and gas fields.

To learn more about our products or speak with a professional, please contact us online today!