Managed-pressure drilling (MPD), considered a novel technique only a few years ago, is becoming a standard tool in the driller’s toolbox for drilling many deepwater wells. This evolution stems from the increasing challenges and risks in today’s well construction operations and the unique ability of MPD to mitigate them. These are applications where process safety is paramount, and narrow-to-nonexistent drilling windows, high pressures and temperatures, wellbore instability, riser gas, and a litany of other issues routinely challenge safety, economics, and the ability to drill and complete the well.
The continued prevalence of MPD in deepwater drilling is being aided through technology innovation. Improvements include advances in real-time analysis, control, and automation as well as enhanced technologies and techniques to integrate the MPD system with the deepwater rig’s systems.
A key enabler in deepwater MPD is specialized rotating control devices (RCD) for use aboard floating drilling rigs. An RCD is a critical component in an MPD system because it is the key element in creating a closed-loop circulating system. In land and platform applications the RCD is located directly above the annular BOP, where it diverts annular flow to an MPD choke manifold. For deepwater applications where the BOP is located on the seafloor, the RCD is integrated into the marine riser.
A few years ago Weatherford developed a deepwater-specific subsea RCD integrated with the riser below the tension ring – a first of its kind. The placement below the tension ring improves installation, riser integration, and overall performance of the MPD system. These development efforts have recently created the latest generation of the RCD, which incorporates a mechanical design that improves operational efficiency and installation flexibility. This is achieved through its slimmer bearing assembly profile that provides more of a plug-and-play compatibility with the range of diameters of riser systems. The mechanical design eliminates hydraulic umbilical lines and controls and uses a self-lubricated, mechanically latched bearing assembly to extend the device’s applicability to well beyond the depth limitations of tethered RCDs.
These RCD advances are the latest innovations in a technology that began as a simple flow diversion device used for air drilling on land rigs. Available today in a wide range of specialized configurations, the much-advanced RCD has become synonymous with a variety of MPD applications that can be performed from any drilling structure, including land rigs, platforms, jack-ups, and dynamically positioned floating vessels.
These benefits have been expanded even further by incorporating the technology with a riser degasing system along with an MPD manifold for floating vessels to help solve riser gas problems – a significant safety and efficiency concern in deep waters.
By enabling the detection of very small gas influxes and preventing their entrainment in the mud system, MPD provides a proactive response that significantly reduces the incidence of riser gas from the onset. The technique is so effective that a riser-degasing event has not been required in Weatherford’s deepwater MPD experience. However, should an influx or entrained gas result in riser gas, MPD provides a controlled means of circulating it out of the riser and dealing with any remaining gas below the subsea BOP.
These advances are key enablers that will contribute greatly to the growth of deep-water drilling. As technology progresses and the industry’s understanding of more effective MPD deployment develops further, this methodology will continue to define the path forward for safely and efficiently drilling a growing portfolio of challenging well prospects.
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