Managed Pressure Drilling fills a key void in the Evolution of Offshore Drilling Technology
Authors: Hannegan Don 
Published: October 2008

This paper speaks to offshore applications of specialized equipment developed for the practice of underbalanced drilling (UBD) where the intent is not to achieve a true state of underbalance at any point in a well's drilling program. The intent is not to produce hudrocarbons while drilling ahead. Instead, the intent is to apply well-proven UBD tools and technology for the purpose of more precisely managing wellbore pressure(s) and annulus returns while drilling overbalanced in marine environments.

Such technology as been coined Managed Pressure Drilling (MPD) or Pressure Management While Drilling (PMWD). By either label, such technology is uniquely applicable to remediate or eliminate entirely a number of drilling-related problems the offshore industry faces today.

Several recent offshore-focused technology transference venues have identified MPD as Enabling Technology for:Low-Head or Near-Balanced Drilling.Variations (3) of Dual Gradient Drilling.Top Hole Drilling alternative to Pump & Dump.Deepwater Drilling with a Surface BOP.Pressurized Mud Cap Drilling.Reverse Circulating.Drilling with Casing.

A tool developed for the safe practice of underbalanced drilling is required for all applications of MPD. Specifically, a Rotating Control Head, aka Rotating Control Device, or simply, Rotating Head. Many in the industry prefer to use the word â??headâ?? when describing the tool as a reminder that it is to be used on the head of BOP stack (atop the annular)) and not in lieu of any component of a typical BOP stack. (API Recommended Practice 53).

In 1995, only about 10% of working land rigs used a RCH for any purpose during a well's drilling program. Today the vast majority of land drilling programs in the U.S. and Canada use a RCH at some point in each well's drilling program, for one reason or another. For whatever the purpose the tool was used, a significantly better "well control incident" track record has resulted, this compared to those onshore wells drilled with conventional open-to-the-atmosphere drilling nipple atop the BOP.

A Rotating Control Head and a dedicated choke manifold affects a closed and pressurizable mud returns system while drilling ahead. This is a required feature not only for the safe practice of underbalanced drilling, but also for Managed Pressure Drilling. Offshore variations of this tool have been developed and proven to practice UBD and MPD in marine environments.

Drilling in marine environments with a "closed & pressurizable" mud returns system and particularily where the intent is not to invite hydrocarbons influx - offers relatively low hanging fruit to overcome a litany of obstacles to conventional offshore drilling.

About one-half of the remaining offshore resources of hydrocarbons, gas hydrates excluded, are economically undrillable with conventional tools and methods. The percentage "undrillable" increases with water depth. Drilling related obstacles to greater economic viability include:Loss circulation/differentially stuck pipe.Slow ROP.Narrow Pore-to-Fracture pressure margins necessitating excessive casing programs and requiring larger, more expensive drill ships to bouy.Shallow geohazards when drilling top holes riserless.Flat time spend circulating out riser gas, kicks, etc.Failure to reach TD objective with large enough hole.

Essentially all of the drilling-related obstacles to economic viability of offshore wells can be addressed, to one degree or another, with a technology that offers more precise wellbore pressure management and control while drilling ahead. Th