ProtoLink developed a real-time calculation engine and associated user interface to determine an appropriate wellhead pressure setpoint for use in a managed pressure drilling (MPD) control system.
The MPD control system aims to maintain precise pressure control at a particular “control” depth in the wellbore for the following reasons:
- to prevent the undesired influx of formation fluids into the wellbore
- to prevent excessive loss of drilling fluid (or mud) into the formation
- to prevent fracturing of the formation
The control depth is typically set to the most vulnerable location in the wellbore; i.e., the point at which the margin between pore pressure and fracture pressure is most narrow.
Precise pressure control is accomplished by adjusting backpressure applied at the surface while fluid is circulated through the drillstring and wellbore. Backpressure is applied by variably restricting the flow of the fluid through a choke. Hence, by controlling the choke, the MPD system strives to maintain the target pressure at the control depth.
Unfortunately, pressure measurements at the control depth are either sporadic or unavailable altogether; therefore, control depth pressure is not a suitable “process variable” in control system parlance. Instead, wellhead pressure, which is readily measured in real-time and which can be related to control depth pressure via a hydraulics model, serves as the process variable. The calculation engine is tasked with determining the proper setpoint for this process variable.
The calculation engine bases its determination on real-time inputs acquired from a rig site historian and from the following types of relatively static data:
- Configuration data
- Mud properties
- Drillstring geometry
- Wellbore geometry
- Depth-indexed target pressures
The historian also serves as the interface between the calculation engine and the user interface, which was developed using Microsoft Windows Presentation Foundation (WPF). The interface contains a three-dimensional visual depiction of the wellbore and drillstring, including an animated representation of the drill bit.