CLD Rigs, MPD Change Equation for Deepwater Well Control

Abstract

Technology Update Closed loop drilling (CLD) systems and managed pressure drilling (MPD) are challenging long-held industry ideas about well control. This realignment in philosophy is happening because of a unique ability to precisely monitor, analyze, and control wellbore pressure in real time. These capabilities are the basis for a growing number of proactive and reactive methods and tools that are solving many conventional well control problems. This is particularly true in the extremes of deepwater drilling, in which managing wellbore pressure plays a principal role in safety, efficiency, and even the ability to drill the well. Fig. 1 presents many of the critical issues addressed by advances in MPD. Although the number of deepwater MPD applications is relatively small, the advantages being achieved with closed loop systems are driving its increased use and the development of specialized deep-water MPD technology and drilling rigs. Monitoring and Control MPD reduces well control events and pressure-related wellbore problems by addressing two key challenges associated with conventional methods: the uncertainty of the predrill model and the inflexibility of the resulting well design and mud regimes. These challenges are overcome by a dynamic capability that is counter to static predrill models. Uncertainty is reduced by very precise measurements of wellbore pressure profiles in real time. Just as important, MPD complements this information with equally precise real-time control. This dynamic solution is proving a key enabler for enhancing safety, efficiency, and operational capabilities in deepwater drilling. To achieve these capabilities, MPD builds on the inherent characteristics of a closed loop system. Within this contained, pressurized wellbore environment, pressure is closely monitored. Pressure changes, such as those caused by an influx, loss, or ballooning, are rapidly detected and controlled in increments as small as a few barrels. Accurate fingerprinting of these minute pressure oscillations quickly identifies the event, which both informs an effective response and avoids a misdiagnosis that can exacerbate the condition. The MPD control response is initiated at the surface by automatically or manually varying the annular backpressure by using a specialized MPD choke manifold. These changes within the closed fluid system are used to manipulate downhole pressure without the delay, cost, and imprecision of changing mud weight. The ability to immediately dial in and hold the desired wellbore pressure changes the well control equation fundamentally with a new set of proactive and reactive pressure management options. Micro influxes that are the precursor to well control events are quickly managed before they can escalate into a kick. When kicks occur, they are rapidly identified, controlled, and circulated out of the well. This mitigates a significant source of risk and nonproductive time (NPT).