Although air and natural gas can be used for underbalanced drilling (UBD), nitrogen is preferred for its minimal risk of downhole fires and a higher level of control. Nitrogen applications for underbalanced drilling can be the most cost-effective solution if produced onsite. This article takes a look at how onsite nitrogen generation plays a significant role in safe and economical UBD operations.
Why underbalanced drilling?
When the pressure in the wellbore and bottom hole is less than the formation, underbalanced drilling is achieved, allowing for production during drilling. Underbalanced drilling minimizes and prevents common issues of conventional drilling, including:
- Formation damage
- Low drilling rates
- Differential sticking
- Lost circulation
A lightweight drilling mud applies less pressure to prevent formation damage and the drilling gases cool the drill bit, which helps to extend the life of the drill.
Why nitrogen for underbalanced drilling?
Underbalanced drilling produces negative differential pressure between the reservoir and the wellbore, encouraging the formation of fluids and gases. Nitrogen is added to the drilling fluid that is pumped directly down the pipeline to displace oxygen, preventing combustion and dangerous reactions between oxygen and hydrocarbons. To a lesser extent, nitrogen is also used to reduce corrosion issues.
Nitrogen applications are more commonly used for UBD, where keeping a low oxygen atmosphere is vital for safety.
The benefits of onsite nitrogen generation
Traditionally, pure nitrogen was purchased and delivered to the site. Although this application can still be used today, it is costly with complex logistics, delivery fees, and high production overheads. Up to 10% of nitrogen is lost during transportation – most companies using pure nitrogen are paying for a product that never makes it to the site. For remote areas, delivering pure nitrogen is tricky and can lead to delays, resulting in a temporary shut down of operations. The downtime is a significant production loss for the oil and gas industry. Additionally, the process of supplying and delivering bulk nitrogen involves an incredible amount of energy and fuel.
Onsite nitrogen is a cost-effective solution for underbalanced drilling operations. By eliminating the logistics of pure nitrogen production and delivery, onsite nitrogen generation comes with the following benefits:
- Reduced operational costs
- Quicker startup times
- No delays, eliminating production loss
- Increased safety of workers with no heavy tanks to transport
- Membrane units can achieve a 95-99% purity level
- Flow rates can be continuously sustained for 24 hours
- Reduced carbon footprint