What is Underbalanced Drilling?
UBD is a specialized drilling technique that is used when protecting the project site’s reservoir, improving drilling performance, and maintaining safety – which are all critical. Unlike conventional drilling methods that rely on heavy drilling fluids, UBD intentionally keeps pressure inside the wellbore lower than the pressure of the surrounding formation.
To do this safely and effectively, nitrogen plays a central role – especially when supplied through Onsite Nitrogen Generation, which provides operators with consistent control, reliability, and enhanced safety in demanding upstream environments.
What Is Underbalanced Drilling | In Simple Terms
In conventional drilling, heavy drilling fluids are used to overpower formation pressure and keep fluids from entering the wellbore. While suitable and effective in many projects, this approach can still damage the formation, which causes slow drilling progress, and can potentially increase the risk of stuck pipe.
Underbalanced drilling works differently.
By keeping the wellbore pressure lower than the formation pressure:
- Reservoir fluids can flow into the well while drilling
- Formation damage is reduced or eliminated
- Drilling rates improve
- Lost circulation and differential sticking are then reduced
UBD is an incredibly valuable solution when it comes to mature reservoirs, depleted formations, and zones with narrower pressure margins where conventional drilling introduces unnecessary risk.
Why Nitrogen Is the Ideal Gas for UBD
To create underbalanced conditions, the weight of the drilling fluid column has to be reduced. This process is then achieved by introducing a gas into the drilling fluid, and while air and natural gas can be used in some cases, nitrogen is more commonly preferred – and for good reason!
Nitrogen is:
- Inert – it does not support combustion
- Non-reactive with hydrocarbons
- Predictable and controllable under pressure
During UBD operations, nitrogen is injected into the drilling fluid and then pumped downhole. As this happens it then displaces oxygen, prevents fires, explosions, and dangerous chemical reactions between oxygen and hydrocarbons.
Nitrogen also helps reduce corrosion in both downhole and surface equipment when in use.
When supplied through Onsite Nitrogen Generation, operators can then gain continuous access to nitrogen throughout the project without relying on bulk deliveries or high-pressure cylinders as many jobsite’s do.
How Nitrogen Helps Maintain the Wellbore Pressure Control
The success of underbalanced drilling depends on maintaining precise pressure control at all times. Even the smallest pressure fluctuations can impact safety and performance overall, therefore it is imperative to have the best crew for the job who know how nitrogen works.
Nitrogen allows operators to:
- Fine-tune the hydrostatic pressure inside the wellbore system.
- Respond quickly to changing downhole conditions.
- Maintain a stable, low-oxygen environment throughout the project timeline.
This level of control is essential not only for UBD, but also for related upstream operations like Managed Pressure Drilling (MPD), coiled tubing drilling, and well intervention work.
With Onsite Nitrogen Generation conducted by experts like Canadian Nitrogen Services, nitrogen is then produced directly from the atmosphere at the wellsite, providing a steady, stable and adjustable supply that supports operations moving forward.
Nitrogen Applications (Oil & Gas)
Underbalanced Drilling (UBD)
Description: Drilling operation where wellbore and bottomhole pressure is intentionally kept lower than formation pressure, allowing the well to produce during drilling while protecting the formation. Nitrogen is commonly used to prevent combustion and, to a lesser extent, reduce corrosion risks.
- Typical Flow: 1,500–3,000 scfm
- Typical Pressure: 1,500–3,000 psig
UBD Surface Equipment Inerting
Description: During UBD operations, potentially explosive reservoir fluids are collected and processed in four-phase separator vessels and surface collection tanks. Nitrogen is used to inert these systems and eliminate explosive environments.
- Typical Flow: ~300 scfm
- Typical Pressure: Up to 4,000 psig
Coiled Tubing Operations
Description: Coiled tubing involves a continuous, flexible pipe used for workovers, drilling operations, stimulation, and fracturing. Nitrogen is injected downhole to stimulate production, clean out debris, and support shallow drilling and UBD horizontal drilling applications.
- Typical Flow: 350–3,000 scfm
- Typical Pressure: 1,000–10,000 psig
Pipeline Purging and Drying
Description: Dry nitrogen is used to displace hydrocarbons, push cleaning pigs through pipelines, dry chemical pipelines to very low dew points, and provide inerting during plant turnarounds and maintenance.
- Typical Flow: 100–3,000 scfm
- Typical Pressure: 300–3,000 psig
Cementing Operations
Description: Nitrogen is added to cement slurry to reduce the hydrostatic pressure column while maintaining compressive strength. This technique is used when formation pressure is too low to support a full cement column while effectively isolating zones.
- Typical Flow: 200–1,500 scfm
- Typical Pressure: 1,000–3,000 psig
Well Completions and Workovers
Description: After drilling, wells are perforated and hydrostatic fluids are displaced to allow the well to flow on primary pressure. Workovers involve routine cleanouts to remove hydrostatic fluids and restore production efficiency.
- Typical Flow: 350–3,000 scfm
- Typical Pressure: 1,000–5,000 psig
Gas Lift Operations
Description: Nitrogen is introduced into produced oil to lighten the fluid column, allowing gas expansion to help carry fluids up to the surface.
This is a secondary process or enhanced oil recovery technique that is used.
- Typical Flow: 300–3,000+ scfm
- Typical Pressure: 1,000–5,000 psig
Nitrogen Flooding
Description: Nitrogen is injected into the reservoir to create a miscible front that pushes displaced oil toward production wells, improving overall recovery rates.
- Typical Flow: 1,000–3,000+ scfm
- Typical Pressure: 1,000–5,000 psig
Reservoir Pressure Maintenance
Description: As natural reservoir pressure declines over time, nitrogen or natural gas is injected to restore energy within the reservoir and drive hydrocarbons to the surface.
- Typical Flow: 1,000–3,000+ scfm
- Typical Pressure: 1,000–5,000 psig
Key Safety Advantages of Using Nitrogen for UBD
Safety is one of the most important reasons nitrogen is used in UBD and other upstream applications in today’s industries.
Key advantages are:
- Fire and Explosion Prevention: Nitrogen easily removes oxygen from hydrocarbon-rich environments, creating an instant suffocation of any combustible or flammable materials.
- Reduced Corrosion: Limiting oxygen exposure helps protect equipment against wear and erosion.
- Operational Stability: Consistent flow and pressure improve drilling performance
- Improved Worker Safety: On-site Nitrogen Generation eliminates the need to transport and handle bulk nitrogen cylinders
Why Onsite Nitrogen Generation Really Makes a Difference
When a jobsite utilizes bulk nitrogen delivery, you can expect high costs associated with it along with logistical complexity, and unavoidable product losses during transport – particularly in remote drilling locations.
With On-site Nitrogen Generation, you receive a more efficient and reliable alternative by having:
- Continuous nitrogen supply with no delivery delays
- Faster startup times
- Lower overall operational costs
- 95–99% nitrogen purity via membrane systems
- Reduced fuel usage and carbon footprint
- Safer worksites with fewer transport risks
Supporting Safer & More Efficient UBD Project Operations
Canadian Nitrogen Services specializes in On-site Nitrogen Generation solutions designed for upstream oil and gas operations, including underbalanced drilling, managed pressure drilling, coiled tubing, well completions, and enhanced oil recovery projects.
With our mobile nitrogen systems, we deliver the reliability, control, and safety required to keep your operations moving – even in the most gruelling environments.
Contact Canadian Nitrogen Services today to learn how onsite nitrogen solutions can support safer, more efficient underbalanced drilling.
