Managed Pressure Drilling (MPD) solutions are no longer the anomaly to Operator strategies, but rather another tool in their belts. With this continual utilization, MPD is evolving to become compact, more effective and safer. The inventive use of a Nitrogen Backup Unit (NBU) has eliminated the reliance of MPD operations on sizable Auxiliary Pumps.
The core function of MPD operations is maintaining the total wellbore pressure by manipulating surface applied back pressure. MPD relies on circulating fluid as back pressure is generated by restricting flow against its choke(s). While drilling, fluid circulation is a given; however, that is not the case during static conditions such as drill string connections. The NBU solves this issue by injecting a small volume of nitrogen into the MPD lines upstream of the choke at a pre-set pressure. This supplements the back pressure control at surface should additional pressure be needed after closing the choke or if pressure diminishes during long static periods.
Prior to the NBU design, the only effective solution was an Auxiliary Pump setup. This solution doubles the choke manifold footprint, relies on mechanical maintenance, and requires additional dedicated personnel at times. Most critically, the Auxiliary Pump lags the operation minutes before each use and is therefore functioned before static conditions when possible. However, unplanned and sudden events are commonplace – such as Rig Pump failures. When drilling formations with narrow pressure margins, unsafe gases, or crucial hole instability pressure limits, a few minutes can result in considerable and costly outcomes. Once installed during initial rig-up, the NBU is capable of injecting nitrogen-sourced back pressure instantaneously at the literal click of a button – avoiding costly and sometimes hazardous conditions.
The NBU modernizes MPD operations and renders the Auxiliary Pump setup outdated in many applications. This paper details this innovative implementation of maintaining wellbore pressure, highlights several field examples of the NBU maintaining back pressure at critical times and shows how the layout used minimizes the operational footprint.