Case study: First Deployment of a Subsea Well Foundation by Jack-up Rig with Surface Wellhead

This summary is based on the paper "Case Study: First Deployment of a Subsea Well Foundation by Jack-up Rig with Surface Wellhead," presented by J. Young, D. Gourlay, G. Mathieson (TotalEnergies E&P UK Ltd), and W. Mathis, J. Alsvik (NeoDrill AS) at the SPE Offshore Europe Conference and Exhibition. The full paper can be accessed through the Society of Petroleum Engineers.

Essential Highlights

• First-of-its-Kind Deployment:

  • The Conductor Anchor Node (CAN) technology was used for the first time with a Heavy Duty Jack-Up (HDJU) rig and a surface wellhead in the high-pressure, high-temperature (HPHT) Isabella Appraisal well in the UK Central North Sea.

  • Previously, CAN installations were only done with subsea wells using floating rigs.

• Challenges and Solutions:

  • The well's location featured interbedded sandy and silty seabed, raising risks for conductor instability and cementing issues.

  • The CAN was chosen to improve conductor stability and reduce wellhead movement, addressing past issues seen in nearby offset wells.

• Installation Method:

  • The CAN was deployed using the HDJU rig itself, eliminating the need for a separate construction vessel and reducing project costs.

  • The rig's drawworks were used to lower the CAN, and a remotely operated vehicle (ROV) applied suction for seabed penetration.

  • The system ensured the CAN remained stable and within acceptable inclination limits during installation.

• Operational Results:

  • The installation was successful, achieving targeted penetration and inclination while preventing conductor movement.

  • The technology improved fatigue life by securing the conductor at the seabed, allowing drilling without further stability issues.

  • Recovery operations were performed with a Construction Support Vessel (CSV) for economic reasons, with the CAN showing minimal wear and readiness for reuse.

• Conclusion and Future Implications:

  • The case study demonstrated the feasibility of using CAN technology with HDJU rigs for challenging conditions, showing potential for significant cost and time savings.

  • Future projects should consider factors like weather, soil conditions, and rig capabilities for similar deployments.

Abstract

This case study highlights the first-ever deployment of a Conductor Anchor Node (CAN®) well foundation with a surface wellhead on the HPHT Isabella Appraisal well in the UK Central North Sea, using a heavy-duty jack-up rig. Unlike previous applications with floating rigs, this installation was carried out with the jack-up rig on-site, reducing costs and risks. The foundation was installed offline during pre-spud operations, using a drillstring and ROV to apply suction for precise placement. The technology provided structural support, improved fatigue life, and enhanced cementing quality, addressing key challenges in shallow formations.

Introduction

In the UK Central North Sea, HPHT wells using a heavy-duty jack-up rig with a surface wellhead face challenges with conductor instability due to difficulties in achieving proper cementing at the mudline, especially under extreme pressure and temperature conditions. Traditional solutions relied on costly remedial cementing, but for a recent HPHT well in sandy seabed conditions, a suction anchor well foundation was introduced to proactively address this issue. This marked the first use of the technology with a surface wellhead and HDJU rig in such conditions. The paper details the engineering design, installation method, and results of this novel application, highlighting its potential for future use.

Challenges Associated with Well Surface Location

During the planning of the HPHT appraisal well, the proximity to a shallow Coal Pit channel with silty clay and sand presented a high risk for conductor instability and cementing issues. Offset reviews revealed similar wells in the area experienced significant problems, including conductor movement, failed cement jobs, and wellhead instability. In particular, the nearby Isabella Exploration well faced conductor movement after cementing, adding complexity and risks to operations. Given the potential for winter operations, a long well duration, and the importance of a stable conductor for the well's design, it was decided to use the well foundation technology to proactively mitigate these risks and ensure a competent foundation.

Solution identified: Well Foundation

The well foundation technology, introduced in 2006, was identified as the solution to reduce tophole delivery risks for the HPHT appraisal well. Consisting of key components such as a skirt section, top lid, guide pipe, and landing shoulder, the well foundation provides a stable foundation by increasing the surface area interacting with the surrounding soil, mitigating conductor instability risks. Additional aids like a water injection system and Integrated Measurement Stab (IMS) were added to address the sandy seabed conditions and ensure successful penetration. A geotechnical study confirmed the feasibility and load capacity of the suction anchor, ensuring it could support the well’s casing strings even in the case of a failed cement job. The foundation’s design reduces wellhead movement, improves fatigue life, and centralizes the conductor while the cement slurry sets, minimizing risks of poor cement bonds caused by conductor movement during standalone operations. The foundation also provides sufficient axial load capacity, ensuring stability in the event of cementing issues.

Installation Concept Selection

After selecting the well foundation technology, the next step was determining the installation method. Traditionally, well foundations were installed by a dedicated vessel with a crane and ROV, but this had only been done on subsea wells drilled by floating rigs. For the HDJU, the team identified risks with the conventional method, including potential misalignment between the rig and foundation and seabed disturbance from the rig's spud cans. A new approach was proposed: installing the foundation using the rig itself, eliminating the need for a support vessel and minimizing misalignment risks. A detailed study was conducted to assess the feasibility of this rig installation concept and compare it to vessel-based methods.

Rig Installation Feasibility

The feasibility study for installing the well foundation using the rig rather than a vessel identified several key considerations. First, the unit had to be picked up from a vessel beneath the moonpool, with a shipping frame and shock absorber mitigating the risk of collision. Second, ensuring verticality during suction was critical, with rig skidding adjustments offering limited but sufficient control. Third, the well foundation had to remain central under the rotary table, with drillpipe and slack tide used to ensure positioning. Finally, a contingency for re-spudding was confirmed within the rig’s skidding envelope. After confirming feasibility, the rig installation was selected for further evaluation.

Comparison of “Rig Versus Vessel” Installation Options

The comparison between rig and vessel installation methods for the well foundation highlighted key risks and benefits. Vessel installation offers flexibility, allowing the well foundation to be installed before the rig’s arrival and timed for optimal weather conditions, but poses challenges with rig positioning accuracy and potential seabed disturbance due to the rig’s spud cans. This could lead to the well foundation becoming unusable if the rig shifts or disturbs the seabed. In contrast, rig installation offers significant cost savings by eliminating the need for a construction vessel and allows for concurrent drilling preparations. However, it carries risks such as weather delays, equipment failure, or alignment issues during installation. Weather analyses showed a low likelihood of delays, and it was concluded that rig installation presented fewer overall risks and higher economic benefits, making it the preferred method.

Installation Planning

As mentioned above, it was decided to use the jack-up rig to install the well foundation. Since this was the first time this installation method was to be applied in the industry, a meticulous planning and risk analysis process was executed based around the main steps listed below:

• Load-out to PSV (Platform Supply Vessel)

• Transit from manufacturing yard to rig

• Hand-over from PSV to rig

• Installation by rig

Load-out and transit

The well foundation was loaded onto a PSV using a tandem lift with two cranes for cost efficiency. It was secured in a specialized sea-fastening frame, which distributed the load, prevented movement during transit, and guided the lift-off operation. Due to the PSV's limited deck capacity and the need for precise positioning near the jack-up rig, a grillage structure was welded to the deck to support the well foundation, which was then secured with chains for easy disconnection and contingency planning.

Hand-over from PSV to rig

The most critical part of the installation process involves precise coordination between the PSV and the rig to successfully lift the well foundation. Key considerations include exact elevations, position of the PSV relative to the drillstring, and allowable weather conditions. The rigging setup used a 125 mT shackle and 20m pennant to connect the drillstring to the well foundation. Vessel heave was accounted for to avoid re-impact after lift-off. Calculations determined the allowable wave height (Hs) for different lift speeds, and a shock absorber was added to reduce dynamic loads, allowing safe lift-off at a 3.5m Hs. A detailed simulation was used for training and visualization of this complex operation.

Installation by jack-up rig

The installation of the well foundation by a heavy-duty jack-up rig (HDJU) follows a similar process to installation by a construction support vessel (CSV), but with key considerations due to the limited skidding window of the HDJU. A detailed analysis ensured the rig could align properly above the well foundation, allowing for some vertical misalignment between the conductor and guide pipe. The inclination limit was increased from 1.0 to 2.0 degrees to accommodate the HDJU's alignment, while still allowing conductor installation within 1.0 degree. ROV access was optimized by adjusting the heading of the suction funnel interface.

Results / Operational Execution

Installation of well foundation

Hand-over from PSV to rig

The key steps for the well foundation installation involved ensuring the PSV avoided collision with the jack-up rig by using a deflector tied to the PSV’s positioning system. The rig crew prepared the lifting string and performed a dry run to ensure smooth operation. Communication between the drawworks operator, PSV bridge, and installation supervisor was critical. Favorable weather conditions allowed for a lift-off speed of 0.4 m/s without needing a shock absorber. The operation proceeded smoothly, with flawless space-out of the drillstring and stable load transfer from the PSV to the rig.

Deployment and self-weight penetration

During deployment, additional drillstring stands were made to lower the suction anchor to the seabed without needing mid-operation connections. The operation paused at 6 meters above the seabed to wait for slack tide, preventing misalignment. Self-weight penetration was performed in 5 mT steps, reaching 0.6 m penetration with an inclination of 1.2 degrees, within the required 2.0-degree limit. The ROV confirmed alignment, and the operation proceeded smoothly.

Suction phase

After completing self-weight penetration, suction was applied to further drive the suction anchor into the seabed, creating a downward force and fluidizing the sand at the skirt's tip to ease penetration. The inclination reached the upper limit of 2.0 degrees, so the rig was skidded to apply a horizontal force, which gradually reduced the inclination. The final results showed a penetration of 6.2 meters (target 6.0 meters), an inclination of 1.3 degrees (within the target of 2.2 degrees), and an orientation of 330 degrees (target 303 degrees). Despite limited visibility, the disconnection of the lifting slings was smooth, and the rigging was successfully recovered without any issues. The water injection system was not required, as the necessary penetration was achieved without it.

Final operations

After the well foundation was installed, the guide pipe lid was detached and recovered to the surface. The ROV then sealed the water injection valve with a blind plug and opened the cuttings and cement removal system valves for drilling operations. Finally, blind plugs were installed on the pressure measurement and IMS stab receptacles to complete the preparation.

Drilling operations

Drilling operations began with the 36 in. tophole section drilled through the well foundation guide pipe, and cuttings were effectively removed by the ROV applying suction. The 30 in. conductor was run and cemented, with the removal system clearing cement slurry without buildup. No conductor or wellhead movement was observed during the well, and no additional cement job was needed. For well abandonment, the conductor was cut at the base and top of the well foundation, with the top cut allowing for recovery. Minimal cement between the conductor and the foundation confirmed the unit’s stability without cement reinforcement.

Recovery operations

The well foundation recovery was carried out by a CSV instead of the rig, as recovery would have been an online operation, incurring additional rig and drilling costs. Using a vessel was more economical, especially since rig operations ended in January when weather conditions were not ideal for landing the foundation onto a vessel. The recovery process was standard and is summarized briefly below.

Installation of guide pipe lid

The recovery operation followed the reverse order of the installation, starting with the guide pipe lid. It was lowered and secured with four locking screws under ROV assistance. Although a backup bolt pattern was available in case of damage or blockage from cuttings or cement, the main pattern was used without issues.

Pump-out phase

Due to weather delays, the pump-out began before the lifting rigging was attached, lowering the well foundation by 1.2 m. Pumping was paused after the inclination reached 2.0 degrees. Once conditions improved, the rigging was connected, but further movement stopped, indicating water breakthrough (piping) had occurred, preventing pressure build-up.

Lift-out Phase

The ROV monitored the lift-out of the well foundation as tension was gradually increased, achieving a controlled lift-out. Early piping was expected, and the vessel's capacity allowed for up to 170 mT pulling. The well foundation was safely landed on deck, with precautions in place to avoid dropped objects. After transit, all equipment was demobilized, and the well foundation was successfully prepared for reuse.

Conclusions

This case study demonstrates the successful use of a suction anchor well foundation with a HDJU rig and surface wellhead, enhancing conductor stability in challenging seabed conditions, especially in soft sands. The system improved fatigue life and reduced movement, which is crucial for standalone HPHT wells. Additionally, the study shows that the well foundation can be installed using the rig itself, though factors such as weather, rig specifications, soil conditions, and boulders need careful consideration. If done offline, this approach can significantly reduce project timelines and costs.

For more detailed insights, the full paper can be accessed through the Society of Petroleum Engineers.

Acknowledgements

The authors wish to acknowledge the support provided by TotalEnergies’ partners in the Isabella joint venture: Neptune Energy, Ithaca Energy and Energean.

Particular thanks are also given to Darren Richardson and the Shelf Fortress team from Shelf Drilling for their significant contribution to the safe and efficient delivery of this project.

References

Young, J., Gourlay, D., Mathieson, G., Mathis, W., & Alsvik, J. 2023. Case Study: First Deployment of a Subsea Well Foundation by Jack-up Rig with Surface Wellhead. Presented at the SPE Offshore Europe Conference and Exhibition, Aberdeen, UK, 5–8 September. SPE-215583-MS. Society of Petroleum Engineers.