Underbalanced Drilling: General Issues

Managed Pressure Drilling (MPD)

Managed pressure drilling (MPD) is an adaptive drilling process designed to precisely control the annular pressure profile throughout the well. The main idea is to create a pressure profile in the well to stay within close tolerances and close to the boundary of the operation envelope defined by the pore pressure, hole stability envelope and fracture pressure.  MPD uses different techniques to mitigate the risks and costs associated with drilling wells by managing the annular pressure profile. These techniques include controlling backpressure, fluid density, fluid rheology, annular fluid level, circulating friction, and hole geometry in any combination

The International Association of Drilling Contractors (IADC) has defined MPD further by creating two categories. Reactive MPD includes drilling programs that are tooled up with at least a rotating control device (RCD), choke, and perhaps drill string float to safely and efficiently deal with problems that could occur downhole. Proactive MPD includes designing a casing, fluids and open hole program that precisely manages the wellbore pressure profile. This category of MPD can offer the greatest benefit to the offshore drilling industry as it can deal with unforeseen problems before they occur.

While it uses many of the same tools that have been designed for UBD operations, MPD is fundamentally different from UBD in that it involves drilling overbalanced. While UBD is mainly used to prevent damage to the reservoir, the purpose of MPD is to solve drilling problems. UBD allows influx of formation fluids by drilling with the pressure of the fluid in the wellbore lower than the pore pressure. MPD is based on maintaining the pressure between the pore pressure and the fracture pressure of the reservoir. It is set up to handle the influx of fluids that may occur while drilling but does not encourage influx. In summary, UBD is reservoir-issue related while MPD is drilling-issue related.