From Enabling to Optimizing with Controlled Mud Level MPD

The Controlled Mud Level (CML) MPD technique is described focusing on the development of its utilization. Initially CML MPD was used as an enabling technology holding a Constant Bottom Hole Pressure (CBHP) to "Drill the Undrillable" and to manage losses by adjusting the fluid level according to actual well conditions. Today, the approach is more based upon reducing well cost, improving safety, and increasing production. The CML method creates a dual gradient effect when lowering the riser level. By moving the hydrostatic column towards the seabed, the pressure profiles are lower at shallow depths and increasing towards sectional TD following the same trend common for operating windows. Utilizing this effect enables longer sections to be drilled within narrow, or even negative, margins - in some cases even when drilling conventionally. The result can reduce the number of sections required in well design, thus reducing the well cost. A CML system can use the riser as the trip tank for instant notification of volume changes in the well. Keeping the fluid level below the telescopic joint eliminates effects from rig motion. The detection sensors are positioned subsea providing earlier and clearer notification of volume changes. In addition to the volume control for all operations, tripping in and out also becomes a safer and faster process without spending time on displacements, by adjusting the riser level to mitigate the surge and swab effect. For depleted reservoirs the drilling approach can start holding the initial virgin pressure and then reduce the wellbore pressure according to the actual degree of depletion. Managed Pressure Gravel Pack has become an established approach ensuring the Alpha and Beta waves go all the way from the toe to the heel without inducing losses. Improving the completion methods and optimizing the execution leads to better production. The development has progressed to where wells are being planned with CML for purposes beyond the CBHP approach. It is used actively in conventional drilling for regular tasks to optimize operations and enhance safety. Since the CML method enables pressure management regardless of pipe size it is utilized for running casings, wireline operations and completion. This paper describes the methodology of the CML technique and refers to field cases to exemplify how this method is used for extending sections, tripping safer and faster, and increasing production through Managed Pressure Completion.