Case Studies-Offshore Managed Pressure Drilling

Abstract

Abstract Managed Pressure Drilling (MPD) technology has evolved on land drilling programs since the mid-sixties. However, it has been only fairly recently that the technology has found an important niche in the minds of offshore drilling decision-makers. With most of the world's remaining prospects for oil and gas being economically un-drillable with conventional-wisdom casing set points and fluids programs, MPD is now being viewed as a technology which can render a significant increase in economic drill-ability by reducing excessive drilling-related costs typically associated with conventional offshore drilling. This paper will define for the audience the two Categories (Reactive & Proactive) and the Variations of MPD that are being currently practiced or will be practiced in the near future in marine environments:CBHP (Constant Bottomhole Pressure)PMCD (Pressurized Mud Cap Drilling)Dual Gradient (several methods)HSE (Returns Flow Control)Case studies will be presented which speak to MPD applications from both fixed (Jackup, platform) rigs with surface BOP stacks...and from floating rigs (moored semi-submersibles and DP Drillships) with subsea and surface BOP's. There will be an emphasis upon the "drilling trouble zones" benefits of MPD. Operator company objectives of practicing the variations of MPD will be detailed. Stances of various regulatory agencies will be briefly discussed. Definition of MPD The following is the IADC definition of MPD: MPD is an adaptive drilling process used to more 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. Technical Notes MPD processes employ a collection of tools and techniques which may mitigate the risks and costs associated with drilling wells that have narrow downhole environmental limits, by proactively managing the annular hydraulic pressure profile. MPD may include control of backpressure, fluid density, fluid rheology, annular fluid level, circulating friction, and the hole geometry, or combinations thereof. MPD may allow faster corrective action to deal with observed pressure variations. The ability to dynamically control annular pressures facilitates drilling of what might otherwise be economically unattainable prospects. MPD techniques may be used to avoid formation influx. Any flow incidental to the operations will be safely contained using an appropriate process. Introduction Managed Pressure Drilling is an advanced form of primary well control usually employing a closed and pressurizable circulating fluid system that allows greater and more precise control of the wellbore pressure profiles than mud weight and/or mud pump rate adjustments alone. A key characteristic of MPD is that of being able to view the circulating fluids system as one would a pressure vessel. The primary objective of MPD is to optimize drilling processes by decreasing non-productive time (NPT) and mitigating drilling hazards. MPD specialized equipment and the techniques to practice its various methods safely and effectively have evolved since the mid-sixties on land drilling programs to a point where, today, most would agree they are status quo. Although the focus of this discussion will be MPD in marine environments, many of the methods presented have been very well proven on land drilling programs, particularly in the Western Hemisphere.