Ultradeepwater presalt developments are considered among the most challenging projects for the oil and gas industry. With the increasing cost of presalt well delivery, various technologies can be used to optimize rig time, reduce nonproductive time (NPT) and decrease risks to safety and the environment.

Managed-pressure drilling (MPD) has the proven ability to help eliminate or mitigate NPT related to pressure incidents throughout the drilling process. MPD uses a closed-loop system that adds an increased level of environmental protection and allows the use of an automated early kick detection system for increased safety. The Halliburton GeoBalance automated MPD system was incorporated onto two MPD-ready sixth-generation ultradeepwater drillships to provide the control, flexibility and safety required to drill and mitigate these risks. This implementation enabled Halliburton to drill 3,785 m (12,418 ft) in an extremely challenging zone in stable and safe conditions.

MPD equipment (in red) is installed throughout the decks of the drillship. (Source: Halliburton)

Collaboration, training essential

The pore pressure and fracture gradient boundaries in the well presented two marked challenges. First, the bottomhole pressure (BHP) needed to be maintained within a 50-psi window. Second, either a pressurized or floating mud cap had to be suitable for drilling. These challenges associated with ultradeepwater presalt developments led the operator to choose the GeoBalance automated MPD service in conjunction with hydraulic modeling software for optimal adaptability and real-time pressure control.

Additionally, this project would be the world’s first implementation of an MPD surface control system on an MPD-ready drillship. The safe and successful implementation of the MPD system required an engineered approach and close collaboration with the operator from the planning phase through training exercises and during the job execution.

Along with the installation of this equipment and hydraulic software, Halliburton developed a two-tiered comprehensive training program for all parties involved in these operations. The first exercise was designed as an MPD overview with the goal of exposing all operational personnel to the theory of MPD and to the equipment that would be used on this project. The second exercise was designed to expose critical personnel to the procedures and to help them develop a strong understanding of the contingency procedures in the event of kicks or losses.

Losses, kicks handled with technology

As this was the first-ever implementation of an MPD control system on an MPD-ready drillship, the operator decided to use MPD on the 16-in. hole salt section, which allowed all rig crews to become familiar with MPD operations on a live well in a nonhydrocarbon zone. This training in the salt section provided the competencies to react with proper responses once in the reservoir.

The uncertainty of the reservoir pressure created an extremely narrow drilling window that progressively got narrower due to a hydrocarbon gradient. To keep the well within the available hydraulic window, the MPD system was designed to maintain pressure slightly above the highest pore pressure in the reservoir using a statically underbalanced drilling fluid. Running speeds were adjusted to control surge and swab pressures on trips, and the automation with the GeoBalance MPD system mitigated their effects in real time.

Properly managing downhole pressure and staying within a safe “pressure window” required advanced event detection and the capability of the MPD system to react to these events. On the operator’s wells Halliburton used the DetectEv application, part of the hydraulic modeling software that uses well signature patterns for event identification and applies an appropriate response within the MPD system. On these wells the two events of possible concern were incurring losses and experiencing kicks.

Salt drilled in record time

All the preparation and planning resulted in flawless execution of four drilling sections—a total of 3,785 m drilled—using the GeoBalance MPD system at a water depth of 2,000 m (6,562 ft). Manipulating the equivalent mud weight at different target depths with the MPD system made it possible to drill the salt in record time and with no NPT. Precise, accurate pressure control eliminated the need for remedial work commonly seen in salt sections. For additional safety both production sections were designed to use a static mud weight at or above pore pressure while in a hydrocarbon zone.

In both production sections severe losses were encountered, and with the precise control of the MPD system these losses were mitigated rapidly, resulting in massive savings—an estimated $30 million per well. Multiple loss zones were encountered and, with each one, the DetectEv application quickly identified the event, and the drilling team adjusted the BHP accordingly.

Due to mud weight, surface pressure losses and the lower fracture pressure, the MPD system got to a point where it no longer had the ability to reduce equivalent mud weight since chokes were fully open while circulating. At this point, because of the operator’s confidence, the mud weight was reduced to a statically underbalanced fluid. With the reduced mud weight the MPD system was able to eliminate losses and avoid influxes within a 50-psi window. Losses throughout both production sections were as high as 300 bbl/hr, but by implementing proper BHP management and reducing the mud weight the team was able to finish drilling and leave the wells in stable condition, eliminating any further losses.

Without the GeoBalance MPD system these wells would have been undrillable. Each loss event would have required immense amounts of rig time to solve; in the past, these events required the use of remedial cement plugs, which cost days of rig time in addition to the cost of large losses. The GeoBalance automated MPD system enabled the operator to avoid these issues, saving a considerable amount of time and money.

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