Jerry Lee discovers how Marathon and ConocoPhillips teamed up to drill difficult deepwater wells in the Gulf of Mexico using a custom MPD system onboard the Maersk Valiant drillship.
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The drill floor is the heart of the Maersk Valiant. It is from here that the journey towards the oil below the seabed begins. Photos from Maersk Drilling. |
Managed pressure drilling (MPD) has been an enabling technology around the world, but its presence in the US Gulf of Mexico (GOM) has been lacking. Strict regulatory requirements and unfamiliarity with MPD could contribute to the resistance to its adoption; however, a recent campaign by Marathon Oil and ConocoPhillips (COP) could change attitudes in the GOM.
Dennis Moore, Marathon’s senior technical consultant, presented the partnership’s challenges and successes at the 2016 SPE/IADC Managed Pressure Drilling & Underbalanced Operations Conference & Exhibition in Galveston.
COP and Marathon partnered on a six-well campaign in the GOM, which saw two deepwater wells drilled in 2015-2016 using an integrated MPD system on the Maersk Valiant drillship. However, the drillship, which was under a three-year contract, did not have MPD capabilities, leading the partnership to invest in upgrading the system.
Equipment selection
MPD kits for offshore operations are not new. However, the options for MPD equipment on a DP drillship are limited to old technology, and full systems, available through MPD service providers, did not provide the functionality and performance the partnership required. As a result, the decision was made to “cherry pick” all the required equipment and integrate it as much as possible into the existing drilling equipment environment already available on the Maersk Valiant.
There are several advantages to owning the system and choosing the components, according to several companies involved with the project.
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Choke Control and SafeVision Monitoring Station installed in front of the driller. |
“Say one MPD company provides the entire system, they may have the best RCD (rotating control device), but not the best chokes and choke controls,” says Helio Santos, president of SafeKick. “So deciding to buy the different components from various sources gives the operator the flexibility to buy the best components to optimize their system.”
Owning the system also allows operators to use the system any way they wish, or upgrade components without having to worry about breaching a contract.
“The installation and subsequent operations has provided the Maersk Valiant crew with a lot of learning opportunities and raised the knowledge level on both the MPD equipment and the managed pressure drilling process,” says Lars Ostergaard, unit director, Maersk Valiant. “A fully integrated system, also makes it easier and more cost effective to prepare for drilling operations where MPD is required as there is no rigging up or down of equipment.”
Furthermore, there were several shortcomings in existing MPD systems, all of them based on technologies that were typically more than 10 years old. With the narrow fracture margins the operators were expecting to encounter, they required higher precision and control of the choke. With large cuttings, high cutting volumes, and high and low flow rates expected, the available flow control equipment at that time commonly found in the market was sized too small for the job.
During equipment selection, most readily available chokes were 3in max orifice, creating a very high native back pressure induced by the MPD system. As the goal was to use MPD on all phases after the BOP has been installed, with flow rates in excess of 1500 GPM, the use of 3in chokes and small pipe diameter became technically unfeasible. A decision was then made to pursue the development of a 6in choke. “The problem lays in the native back pressure generated by the MPD equipment,” Santos says. “Using 3in chokes, even if the chokes were fully open, there would still be high back pressure as a result of the smaller cross-sectional area. And this high back pressure ‘eats’ the safe mud weight window available, which is usually not big.”
Finding a solution to the issue, CORTEC developed a 6in orifice drilling choke capable of interfacing with the SafeKick Intelli-choke control system, which already had a very good accuracy in position and pressure control. Both the 3in and the new 6in Intelli-Choke achieved the precision required.
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CORTEC MPD buffer manifold – Valiant. |
“CORTEC worked with the Valiant project group to design a 6in orifice drilling choke as well as 3in and 4in orifice pressure relief valves that were capable of providing the control necessary to flow at desired conditions,” says Stephen Corte, vice president marketing and business development, CORTEC.
To handle the larger equipment and minimize frictional losses, the system also required larger 8in nominal piping with 7.0625in bore isolation valves. To this end, CORTEC supplied the buffer, choke, and metering manifolds, but space on a drillship is limited.
“This creates an ideal scenario for ‘compact’ manifolds,” Corte says. “Our compact valve division, CORTEC Manifold Systems, specializes in the design of compact ball valves and manifolds, which optimize weight and space savings while maintaining or exceeding API standards. Utilizing compact ball valve and manifold technology allowed this entire large bore system to fit within a space that is 7ft tall and 11ft wide, running along the rail of the vessel’s moon pool.”
Issues were also identified when selecting an RCD system, which was made more difficult by a host of challenges around sizing compatibility and market availability.
Weatherford, which has a history of successful deepwater rig integrations and experience accommodating the existing riser equipment on the Maersk Valiant, provided a unique RCD system that incorporated an Elite RCD body and latch assembly along with a customized SeaShield model 7875 RCD bearing assembly.
“A sizing modification was required to drift the rig’s upper riser package,” said Neal Richard, MPD project manager, Weatherford. “The RCD’s existing bearing assembly design was modified to accommodate a smaller outer diameter (OD).”
“Marathon and COP ended up deploying the Weatherford field-proven model 7875 RCD bearing assembly in a specially developed Elite riser-based body and latch system to allow for a reduced bearing assembly OD of 18.88in,” says Brian Grayson, director of secure drilling services pressure control, Weatherford.
Bringing all the components together, a control system was required, but the systems with which the operators previously had experience did not offer the sensitivities that this campaign required.
A proportional integral derivative (PID) control system would not work with the dynamic processes of MPD. The hydraulics software lacked accuracy, and the control for hydraulic choke position lacked the necessary precision. The input and output volumes also required greater accuracy, and fluid density information needed to be fed directly into the hydraulics models.
In 2013, Marathon and COP selected SafeKick to provide the control system. The SafeKick control system is comprised of their SafeVision and Intelli-choke technology. SafeVision provides monitoring and real-time hydraulic modeling, and Intelli-choke controls the choke position. The MPD system would be controlled through SafeKick software and equipment, so they worked with the vendors to develop new equipment to improve the systems performance. Using Coriolis meters on all pumps, and manifolds, and connecting the data into the system, the control system could, in real-time, accurately track fluid density, rate, and model the hydraulics in a very accurate way, not seen to date on MPD jobs. For choke control, the system used intelligent predictive control (IPC) instead of PID.
“The system is able to control the choke to an accuracy of 0.003%, or about 5psi,” says Erdem Catak, vice president of operations, SafeKick. “The system is also incredibly easy to use. A crew member could learn how to use it in a couple of minutes.”
Throughout the process of equipment selection and development, the operators, and vendors worked with the US Bureau of Safety and Environmental Enforcement (BSEE).
“We kept our processes transparent, which is important, it shows that we have nothing to hide,” Santos says. “This made the permitting process easier.”
Integration
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Coriolis meter manifold. Photo from CORTEC. |
Traditionally, to use MPD on a well, the driller would need to relinquish control of the well to the MPD service provider. With responsibility of the well still laying on the driller, resistance to using MPD more readily is not surprising.
“How would you feel if you are responsible for the well, and someone else is controlling the pressure in the well,” Santos says. “With the traditional MPD systems, if pressure is increased, the driller is not in control of it.”
The MPD system on the Maersk Valiant, however, is different.
“The MPD system is integrated into the Valiant’s driller’s cabin, so it works directly with the driller, whose responsibility is to apply or reduce the pressure being applied by the MPD chokes,” Catak says. “The driller is taught how the MPD system works and how to use it, and the rig crews are taught MPD as normal operations. So now the control of the MPD system is in the hand of the drilling contractor.”
By integrating the MPD system into the Maersk Valiant’s rig, the driller no longer has to worry about handing over control of the well to a third party; when MPD is required, the driller initiates it.
Moreover, the integrated MPD system became part of the rig’s maintenance system.
“With learnings gained over time, high system uptime was achieved through effective operations, maintenance and spares availability,” Ostergaard says. “Finally, having an integrated MPD system proven in operations make Maersk Valiant a very attractive drilling unit in the market, which can enable operators to drills wells with a tight drilling window or drill more conventional wells safer and more efficiently.”
Without involving a third party, there is also less uncertainty. One of the issues hindering more general acceptance of MPD are the differing standards and policies between the operator, the drilling contractor, and the MPD service provider. Before a campaign can begin, the standards and policies of the three entities must be bridge, but some conventional policies are challenged by MPD operations. In the case of the Maersk Valiant, however, this is a non-issue: the MPD provider is the drilling contractor.
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Delivered in 2013, the state-of-the-art drillship measures a total of 228m (748ft). |
Training
With the MPD system integrated into the drilling system, the crews from Marathon, COP, and the Maersk Valiant needed to learn how to use it.
Brought on early in the project development for their MPD experience, Signa Engineering Corp. was familiar with all phases of the operation, and were chosen to facilitate the training program.
Although SafeKick provided training for software control and operations, a Signa project team, and Marathon and COP MPD experts, developed all of the training curriculum: MPD operations, hydraulic modeling, simulated and hands-on choke operations, and drilling connections.
“The primary objective was to develop a training program that facilitates efficient and safe MPD operations, while meeting or exceeding all regulatory requirements,” said Bob Goodwin, senior operations engineer at Signa.
“The vast majority of the training was performed using the actual MPD equipment spread on the Maersk Valiant,” Goodwin says. “This included simulated operations and contingences, as well as the mentor-supervised on-the-job training (OJT). The initial [rig-based] training was performed in multiple 2-4 hour sessions, but continuous OJT was performed throughout the drilling programs.”
Case Study
With the system integrated, crew trained, ABS-CDS certification, and BSEE approval to take the mudweight below pore pressure, Marathon spudded the Solomon exploration well on Walker Ridge Block 225, in mid-May 2015. The first well of the six well campaign, Soloman was successfully drilled to over 34,600ft, into the lower tertiary target interval, but the well came up dry.
After the well was plugged and abandoned, the Maersk Valiant was transferred to COP, and the second well, Melmar, was spudded in December 2015, in Alaminos Canyon Block 475. The well was successfully drilled to over 29,000ft, into the lower tertiary Wilcox target, however, non-commercial quantities of oil were encountered, and the well was also plugged and abandoned. At the end of April this year, COP opted not to finish their remaining two wells, Horus and Socorro. The Maersk Valiant has since been hot-stacked.
Although, both wells came up dry, the Maersk Valiant was able to drill well sections overbalanced, with mudweight below pore pressure, detect influx in less than 1 bbl, mitigate wellbore breathing effects, trip with no losses or gains when the operating window was minimal, and conduct dynamic wellbore integrity tests during drilling operation.
“ConocoPhillips, Marathon and Maersk Drilling has proven that MPD can be used in US GOM to drill wells that are difficult to drill with conventional methods,” Ostergaard says. “MPD was new to most onboard the Valiant. The crews adapted well and the drillers have done an excellent job. Now time has come to take all the learnings and make some more formalized training programs with Maersk Training and the structure of this is currently being discussed.”
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