Variations of Managed-Pressure Drilling Currently Practiced:Offshore Case Studies (2006)

Abstract Managed Pressure Drilling in marine environments is well on the path of widespread understanding and industry appreciation of potential for the technology. From years of evolutionary development on land programs, particularly in the United States and Canada, a number of offshore drilling decision-makers have now become ‘first adopters’ of this technology with significant success and with good control of the well at all times during the drilling process. Perhaps the best way to quantify this statement is to mention that, to date, all first adopters of MPD from offshore rigs plan future MPD projects. Unlike conventional circulating drilling fluids systems that are open to atmosphere on the rig floor, MPD tools and technology enable the circulating fluids system to be likened to the hydraulic characteristics of a pressure vessel. Several variations of MPD enable the effective wellbore pressure profile (e.g., equivalent mud weight) to be adjusted significantly with mud in the hole at the time, particularly beneficial when drilling in narrow formation pore pressure to fracture pressure margins and when the pressure environment limits may be relatively unknown. One variation of MPD addresses severe loss of circulation and excessive mud costs. Another addresses employee health, safety and environmental aspects that may be associated with drilling with conventional opento- atmosphere mud returns systems at the rig floor. A closed and pressurizable mud returns system is the enabling technology for most, but not all, applications of MPD. Drilling with a closed mud returns system reflects a relatively modest step change from conventional methods; most offshore rigs can accommodate the specialized equipment space requirements, benefits vs. cost are attractive, and the‘MPD way of looking at drilling hydraulics’ is relatively easy for drilling decision-makers and regulatory agencies to comprehend. Therefore, this paper will speak only to the ‘lower hanging fruit’ MPD techniques that are enabled by drilling with a closed and pressurizable mud returns system orannulus. More precise pressure management throughout the wellbore is an objective of all variations of MPD. Unexpected downhole pressure environments may be dealt with more efficiently with enhanced control of the well and usually with less interruption to the drilling program when such surprises are encountered. An influx of formation fluids is not invited in MPD. Although some MPD tools and techniques are rooted in Underbalanced Drilling technology, this is a major distinction between MPD and UBD. A properly planned and implemented MPD program is likely to see fewer hydrocarbons produced to the surface that if the prospect had been drilled conventionally. This work will define MPD, introduce the audience to its unique terminology and explain its Variations with pressure-depth maps. As each variation addresses specific well construction and drilling challenges, examples of each that have been practiced to date will be described. In consideration of operator confidentiality, several that are in the advanced stages of planning willbe addressed only in very general terms.