Nitrogen gas injection for immiscible gas flooding is commonly used in the oil and gas industry, and can improve oil recovery by increasing reservoir pressure during the tertiary stage of recovery. Crude oil development and production includes three phases: primary, secondary, and tertiary recovery.
Primary recovery stage
During the primary recovery stage, the natural reservoir pressure pushes oil into the wellbore and lift techniques, such as pumping, bring the oil to the surface. Approximately 10 percent of the reservoir’s original oil in place is typically recovered during this phase. Continual reduction of the well’s drive pressure can make recovery of remaining oil challenging. Techniques such as fracturing, stimulation, and gas lift are often used to assist and sustain the initial gas drive.
Secondary recovery stage
During the secondary recovery phase, techniques such as water or gas injection are used to displace the oil and force it to a production wellbore which results in the recovery of an additional 20 to 40% of the original oil in place.
Tertiary recovery stage
During the tertiary stage, gas injection can be used. With this technique, nitrogen (immiscible), or carbon dioxide (miscible) gas is injected into the oil reservoir (U.S. Department of Energy, n.d). This technique is also called gas flooding which can be either miscible or immiscible. In miscible gas flooding, the gas (CO2) mixes with the oil to reduce its viscosity and improve flow. In immiscible gas flooding, the gas (nitrogen) does not mix with the oil, but rather, creates energy which increases pressure to drive the oil into the wellbore and promote additional recovery (Gasflooding.com, 2013).
Benefits of nitrogen gas injection
Gas injection is typically utilized in older reservoirs, where the current production rate is no longer economically viable. Nitrogen is injected into multiple wells distributed throughout a formation to force the oil into the production well for recovery. Nitrogen injection can improve existing production by as much as 200-300%. Gas injection with nitrogen has significant benefits over the common alternatives, such as carbon dioxide or natural gas, because it is inert, noncorrosive, and oxygen-free.
Nitrogen can be obtained through bulk liquid truck deliveries to the production site or via an on-site nitrogen gas generator. Relying on a purchased supply of nitrogen has several drawbacks including:
- The possibility of running out of gas. Some enhanced oil recovery applications can require a significant amount of nitrogen (250 scfm at > 1,000 lbs of pressure) depending on the size and depth of the well.
- The inconvenience associated with contract negotiations, scheduling deliveries, and delivery fees.
An on-site Parker nitrogen generator that separates nitrogen and oxygen from compressed air, offers significant benefits over delivered nitrogen. These benefits include:
- Continuous production of nitrogen to the application purity requirement
- High flow capabilities in a compact, easily transportable container.
All systems can be designed for low or high pressure feed air sources, giving the user the option of utilizing plant air or a multi-stage compressor. No other membrane system can offer the flexibility and feed air options for both onshore and offshore applications.
Read this marketing application publication on using nitrogen for enhanced oil recovery.
This post was contributed by Judy Silva, Gas Generation Technology Blog Team Member, Parker Hannifin.
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