What is a Narrow Operating Window?
Narrow operating windows occur when there is a small difference between the pore and fracture gradient and/or other wellbore stability gradients. This challenge is commonly encountered in many deepwater wells in addition to drilling through salt plumes, depleted reservoirs, and weak formations.
Why is This a Challenge?
Slight changes in the bottom hole pressure can lead to fluid loss and influx in the wellbore. Ultimately these events lead to Non-Productive Time and potential well control incidents. As the operating window narrows these drilling hazards become more acute. Sometimes the operating window is so narrow conventional drilling is not feasible.
What Are Your Options To Deal With It?
Drill conventionally while limiting drilling parameters to stay within operating window. This often means that lost circulation is highly likely and additional mud volume must be planned, sometimes in combination with using a specially engineered drilling fluid(s) and limiting drilling rate to assists in maintaining the bottom hole pressure within the operating window. Overall drilling conventionally results in a higher risk of not reaching planned depths and well control incidents.
- Add sections to well design in order to safely drill and isolate the formations(s) in the narrow operating window.
- Use a Managed Pressure Drilling technology to adjust the bottom hole pressure to achieve standard drilling rates and safety margin throughout the operating window.
The most common MPD technologies include:
- Surface Back Pressure (SBP)
- Controlled Mud Level (CML)
- Continuous Circulation System (CCS)
How EC-Drill® can help you when drilling Narrow Operating Windows
EC-Drill® is a Controlled Mud Level technology that controls the bottom hole pressure and gradient by adjusting the fluid level in the riser. It enables the use of a heavier drilling fluid while achieving lower circulating bottom hole pressure when compared to conventional drilling. Thus, EC-Drill® increases the static overbalance pressure and reduces the risk of losses when circulating, while being able to keep bottom hole pressure constant. A robust solution for successfully drilling in Narrow Operating Windows.
In areas with challenging top-hole conditions, such as unconsolidated sands, it makes sense to commence drilling the top-hole with engineered, weighted fluid as you would for the down-hole sections of a well.
However, there are environmental issues to consider. The RMR® (Riserless Mud Recovery) system enables the use of engineered fluid even in environmentally sensitive areas thanks to its closed-loop design.