Managed Pressure Drilling for Brazil’s Pre-salt

The definition of MPD recently adopted by the IADC Underbalanced Operations and Managed Pressure Committee states that: “Managed Pressure Drilling (MPD) is an adaptive drilling process used to precisely control the annular pressure profile throughout the wellbore. The objectives are to ascertain the downhole pressure environment limits and to manage the annular hydraulic pressure profile accordingly.”

According to drilling specialists, bottomhole pressure is normally maintained above pore pressure by controlling the density of the drilling fluid. When density gets too high, the formation begins to absorb the fluid and the fluid density needs to be adjusted. Casing must be run to isolate the open hole before drilling can continue. The common objective of all currently known managed pressure drilling techniques is to stretch or eliminate casing points to allow drilling beyond conventional limits of depth or pressure variation.

Petrobras has been experimenting pressurized mudcap drilling and other forms of MPD since 2005, beginning onshore and in shallow water. For a few years now Petrobras has been experimenting in deep waters, to the point where their drilling specialists believe it is the best solution for pre-salt drilling. Petrobras is now targeting three or more fully MPD capable ultra-deepwater rigs for the Libra field in an ongoing tender. MPD was used successfully on wells at the Franco South, Iara and Lula North fields.

The technology proved to be very efficient in the complicated deviated entrances to pre-salt reservoirs, making these difficult wells viable and reaching targeted depth, where other drilling technologies may have failed. MPD has proven to also be capable of increasing productivity, improving drilling safety and possibly even giving the operator new options for circulating gas kicks. Until recently, Weatherford was the sole manufacturer of the MPD system, although Aker is now also in the market after its 2013 acquisition of Managed Pressure Operations Ltd.