Managed Pressure Drilling has been proven to be a tool for extending access to previously unattainable drilling targets in many deepwater areas across the world, such as deepwater Gulf of Mexico. 21" Low-Pressure risers do not allow for application of Constant Bottom Hole Pressure (CBHP) technique by floaters. Since it is not designed to hole the pressure, it prevents setting up a closed circulation loop in our drilling system which is an essential tool for MPD.
A high-pressure riser along with a surface Rotating Control Device is required to perform CBHP drilling technique. However, we know that deployment of such high pressure risers in long lengths and harsh environments has not come to be practical.
An alternative drilling method from floaters at any water depth proves to be Reelwell Drilling Method (RDM). Reelwell AS, Shell, StatoilHydro, and the Research Council of Norway launched a JIP in 2005 to develop RDM, which is a riserless drilling method based on concentric drill pipe. Mud is circulated in a closed loop in this system. The pressure and flow of mud is dynamically controlled by a computer system on the return path on the surface. Many tests including the latest pilot test in March 2009 has proven that the downhole pressure can be controlled precisely and that the system fits perfectly for CBHP.
Deployment of this technology by smaller floating rigs is possible with no limitation on water depth as huge and long 21" LP riser is eliminated from the system. The volume of mud is limited to bring about even more cost and rig space savings.
Drilling challenges addressed by MPD are typically related to maintaining the equivalent circulating density (ECD) within the drilling window between formation pore pressure (or wellbore stability pressure in some cases) and the fracture pressure of the section being drilled. This balancing act occurs in narrow and relatively unknown downhole pressure environments, and frequently results in loss/kick, well control scenarios, differential sticking, risk of twist-offs, and slow penetration rates (Hannegan 2009).
A risk assessment study recently done in conjunction with the Drilling Engineering Association determined that, properly applied, MPD has a high probability of mitigating most, if not all, drilling-related risks (Hannegan 2009).
"Managed pressure drilling continues to demonstrate its bright future," the DEA study observes, noting that there has not been any recorded incident of a kick while applying the techniques of managed pressure drilling. "This is not to say that there have been no problems," the report states. "Sometimes pipe gets stuck, and lost-circulation problems still exist, but not the same magnitude as in conventional drilling" (Hannegan 2009).
MPD has been proven to be a perfect tool in terms of NPT reduction in well drilling operations in land and offshore. Application of MPD for subsea wells become of even more importance as NPT is significantly more costly in offshore. MPD has much more to offer offshore drilling programs than the land drilling programs that pioneered the technique. Wellbore hydraulics for the majority of the world's remaining prospects will unquestionably be more challenging than has been enjoyed in the past. Depletion and the requirement to drill in deeper water further aggravate the challenge. Most experts would agree that most of the easy prospects have already been drilled. For offshore assets, managed pressure drilling, in all its variations and combinations thereof, is providing a novel means of dealing with a litany of drilling related hazards. As part of a suite of controlled pressure drilling technologies for reducing costs, improving production and mitigating downhole problems, MPD joins drilling with casing and expandable tubulars in providing state-of-the-art drilling hazard mitigation capability (Hannegan 2009). However, moving the technology to floating rigs is not that easy, and becomes to be associated with a lot of challenges.