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| The newly-built, ultra-deepwater drillship Rowan Renaissance was modified and optimized for MPD operations. Photo courtesy of Rowan Companies. |
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A trifecta, consisting of an operator, drilling contractor and service company, undertook a proactive approach to integrating unique riser equipment and surface control systems into a newly built, ultra-deepwater drillship. The objective was to facilitate a rapid transition from a traditional rig to one with managed pressure drilling (MPD) capabilities. By so doing, they were able to provide a semi-permanent installation with the means of immediate conversion to closed-loop drilling (CLD) when required, thus eliminating typical MPD rig-up preparation of 12–14 months.
MODIFICATION CHALLENGES
The use of conventional “open to atmosphere” drilling methods on challenging deepwater wells is now becoming insufficient to achieve well objectives safely, on-time and on-budget. In some cases, it can even mean that prospects are deemed undrillable. One recent emerging industry trend is to incorporate the use of riser gas handling (RGH) systems as an additional safety feature to protect rig personnel from a gas-in-riser situation (one of the biggest risks of deepwater operations). Although these systems are a welcome addition, such adoption of new technology should go a step further than just being a reactionary safety system. Instead, the goal should be to prevent these events from occurring in the first place. What is needed is a pro-active approach, one that provides for early detection of a potential hazard and swift preventative measures. As a result, MPD systems are becoming the go-to approach for equipping modern rigs to address some of the problems encountered while drilling challenging deepwater wells.
Despite the successes achieved with MPD, its use on deepwater drilling vessels is limited by a host of constraints, including cost, equipment availability and deployment. To fully realize its potential requires a focused, collaborative effort to develop guidelines, procedures, equipment standards, rig modifications, design and, above all, training. Extending these MPD advantages to a broader scope of deepwater wells can offer safety, operational and economic rewards. But deployment can be hampered by the inability of deepwater drilling vessels, originally built for conventional open-to-the-atmosphere circulating systems, to readily accommodate an MPD system.
This lack of readiness manifests itself in a number of ways. Dimensional restrictions, such as rotary table, diverter and upper riser package IDs and ODs, are the most obvious issues to overcome when integrating an MPD riser joint. Secondly, depending on MPD variants, flexibility in fluid flow paths requires careful consideration to topside manifold design, piping, cabling and instrumentation. The least obvious bottleneck is the seamless integration of the hardware, software and procedures, to achieve successful MPD service delivery. This is imperative, to be able to respond immediately to dynamic wellbore events.
In the move toward MPD readiness, modified rigs will have enhanced RGH systems; but to be fully MPD-capable, more upgrading is generally required, such as topside pipe work, data/communication networks, higher volume separators, and changes in riser architecture. In under-construction and newly built rigs, these needs can be addressed readily. But in existing rigs, modifications can be problematic.
One of the significant issues encountered over the past several years has been the requirement for larger ID slip-joints, to allow placement of the MPD RCD below the slip joint (larger ID required for passage of the RCD bearing assembly), given the current lead times involved with sourcing marine riser components. Solutions to this problem are already being developed in the form of slimmer bearing assemblies. In the case study described in this article, the drilling contractor upgraded the planned slip joints to 19¾-in. ID, prior to the availability of the slimmer bearing assemblies.
INDUSTRY COLLABORATION
In 2012, Repsol entered into an agreement with Rowan Companies to lease the first of four, planned new drillships to be built in Korea. Initial specifications for the rig involved the incorporation of a RGH system into the design. Following experiences in recent deepwater operations, Repsol decided to review its requirements and include MPD/CLD capabilities. Since the drillship was in an advanced stage of construction, the incorporation of MPD capabilities into its final design presented significant challenges. A collaborative approach was needed between the operator, the drilling contractor and the service company (Weatherford) to requisition and install the MPD equipment, Fig. 1.
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| Fig. 1. Longitudinal Moonpool layout shows how the integrated piping and instrumentation allowed an RGH package to operate, as required by MPD operating procedures. |
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Repsol previously had experienced some severe well problems in analogous wells, which resulted in significant time penalties. As a result, the operator recognized that the use of MPD was a prerequisite for reliable drilling operations with the new drillship. Rowan Companies recognized the need for MPD and wanted to offer a level of MPD readiness, which was not available in other newbuild vessels. As an MPD service provider, Weatherford was able to supply the peripheral equipment required to augment the RGH system and manage all the integration needs. A decision was made to design certain pieces of the vessel’s RGH package to be compatible with Weatherford’s below-tension ring RCD. The RGH surface manifold was also designed to accommodate Weatherford’s Intelligent Control Unit (ICU), available electronic monitoring and control system, and automatic chokes, Fig. 2.
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| Fig. 2. RGH manifold (left) with MPD functionality (PRV, automated chokes and flowmeter), permanently built into the rig, and designed to function automatically as instructed by the Microflux ICU (right). |
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Following several meetings among the three entities, a detailed plan was derived to meet the existing time constraints. This plan incorporated detailed procedures for the installation of all of the surface piping and instrumentation required to integrate the MPD equipment with the RGH system, into a package that would allow for CLD operations to be performed. MPD systems use much of the same equipment as RGH (such as the riser annular, flow spool and surface flow diverting manifold).
Since preventative MPD operations are more frequent than reactive RGH operations, it was logical for the MPD service provider to undertake the integration of the whole system to assure the operability of the RGH, and surface flow diversion was a seamless process. Included in the plan specifications were sets of bridging documents and procedures, which were developed and fully understood by all parties through detailed training sessions. Additionally, well control boundaries were set and responsibilities clearly assigned.
MPD CONVERSION
When the final decision was made to incorporate a CLD/MPD system, the drilling vessel was in an advanced state of fabrication, and a timetable had already been compiled for its completion and eventual deployment. Repsol wanted to adhere to this schedule. A Weatherford team was deployed to Korea in July 2013 to carry out a detailed survey of the vessel, and to prepare a program for the installation of the MPD facilities.
Prior to this survey, work had already commenced in ordering/sourcing the required long-lead equipment. Detailed discussions were held with Rowan’s subsea, drilling and engineering teams to ensure the accuracy of the survey, the practicality of the resulting installation plan, and adherence to the timetable. Full written operating procedures, hazop evaluations and rig crew training were to be completed, as appropriate, during this timetable.
MPD INSTALLATION AND RIG MODIFICATION
The equipment installation and all necessary rig modifications were discussed, and approved, on an ongoing basis while the ship was proceeding to its ultimate destination, Fig. 3. The major items installed, prepared for future use, and checked included:
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| Fig. 3. The RCD riser spool, redesigned to incorporate RCD and allow riser choke, kill, boost and conduit lines to bypass to termination joint at tension ring. |
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Microflux control (MFC) system, which provides a range of methods to precisely monitor, manage and control unexpected events in drilling operations. Suitable space was available on the drill floor for its installation.
Intelligent control unit (ICU). Given that Weatherford’s standard MPD manifold was not used, an ICU had to be custom-built. The ICU provides for both pressurized mud cap drilling (PMCD) and constant bottomhole pressure (CBHP) drilling operations; precise management of the wellbore pressure profile; wellbore and surface safety system monitoring; and early detection and control of kick/fluid loss incidents.
The RCD unit and operating ancillaries were tested at a Weatherford facility in Louisiana. The RCD riser spool piece design incorporated the riser choke/kill/boost/conduit lines, Fig. 3. This approach was a major departure from previous BTR MPD applications, which required a choke/kill/boost/conduit termination joint, with very long hoses back to the moonpool, to be positioned beneath the MPD riser joint.
The MFC manifold was accommodated within the existing RGH manifold by designing a system, which allowed for a quick retrofit to incorporate two automatic drilling chokes and a Coriolis flowmeter loop for accurate measurement of return mud flow. The addition of a separate, compact panel for data acquisition and automation of the drilling chokes, responding to the Microflux ICU, makes this a true MPD rig.
Other items checked, installed and/or modified included:
- Determination of the riser stack space-out for the RCD installation and evaluation of the existing components to identify any additions and/or modifications required.
- Identification of suitable locations for the installation of the RCD hydraulic power unit (HPU), and the auxiliary equipment and pipework.
- Checking that the availability of mud supply from the rig pumps is adequate to maintain the circulation of mud across the well during connections.
- The location and wiring of all panels for operators, drillers and remote panels, and the system database.
- Checking the availability of adequate power, utilities and communications. A Variation Order was signed with the shipyard to install the required junction boxes and cabling at various locations around the rig. This proved to be a very wise move, given the difficulties in trying to do this work post-delivery from the shipyard.
- Verification of the installation of stroke counters on the rig pumps.
- Identification of all planned piping routing and accurate determination of the required dimensions. The original plan was to have the shipyard install the necessary permanent pipework during the construction phase. Due to the tight schedule however, Weatherford provided the pipework.
- Preparation of a detailed installation report, complete with drawings, as needed.
All of this associated work was completed prior to rig arrival on the first MPD well location.
COLLABORATION SUCCESS
This entire MPD modification operation presented significant challenges to all the participants in logistics and installation operations, but it was completed, as planned. The MPD system will be ready for deployment on the first required well offshore West Africa.
Rowan, with Repsol’s support and encouragement, strove to integrate all of the changes into making the rig look and feel like similar units, but with greatly enhanced versatility to enable it to address the MPD challenges. The intricacies involved in these modifications could not have been achieved without very close collaboration between the three entities involved, which provides a model for future such undertakings. 
ACKNOWLEDGMENTS
The authors thank Repsol, Rowan Companies and Weatherford for their permission and encouragement to present this article.
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