Drilling through a jacket: Challenges & solutions

Posted by Ann Vicens on 13-May-2019 14:00:00

The development phase of an offshore installation can be time-consuming, often involving great upfront expenditure. The prospect of drilling before the installation is completed gives operators the chance to bring wells online ahead of schedule, therefore improving the overall economics of a project through early oil production, which achieves both time and cost savings.

Everything you need to know about drilling through a jacket

There are two main pre-drilling options; drilling through a template or through a jacket (the jacket refers to all the guides and legs of the platform). With the first option, drilling can commence before the jacket is ready and before an optimum number of pre-drilled wells are determined. Although this option offers the greatest gains in terms of time, the tieback will be performed at subsea level which adds a level of complexity and risk to the operation which would need to be managed. The other option is drilling through a jacket which allows pre-drilling before the top sides of the platform are completed. The time gain is not comparable to drilling through a template, however, the tieback and reconnection activities take place at surface level making the operation easier. Both development methods are valid, but the project specifics, risks, financial information and market conditions will ultimately dictate which option is best on an individual project basis. Newly available technology and industry lessons learned have helped to develop these processes to allow oil and/or gas to be produced soon after platform/topside installation. 

Here are Claxton’s considerations for operations when drilling through a jacket to help keep your project on track.


Whilst drilling through a jacket can bring tangible benefits to a development project, rig availability will play a part in the decision-making process. Wells can be brought online sooner with the pre-installation of the conductors, enabling the utilization of lower cost platforms to support offshore installation so, if the infrastructure and personnel resources are available, drilling through a jacket should be considered.



THE PROBLEM: Centralization is still a key issue for the structural integrity of the conductors and can present numerous issues during the development phase. Problems encountered during spudding and cementing can be particularly challenging and cause misalignment issues between drilled wells and the platform jacket. Centralization of the conductors within the guides also must be considered to avoid a negative effect on the life of the well and structural guides of the platform.

THE SOLUTION: When addressing challenges with the centralization of the drill collar/string, the use of drill bushings can guarantee a central top-hole during spudding. The drill bushing centralizes the drill string/collar during spudding preventing the occurrence of considerable misalignment between the conductor and the jacket guides.  

Once the first section has been drilled centrally, the conductors can be run without major offset induced issues. Conductor guide centralizers are ‘bolt-on’ devices that do not hazard the integrity of the casings. Significant conductor, jacket and flow line damage can occur if centralizers are omitted or not designed correctly; so, it is vital to choose the correct centralizer for the job. Claxton can advise on the best options for centralization of drill string/collar, conductor and casing for the specific project. Early engagement with clients allows Claxton to implement measures that will allow the use of the most cost-effective designs with fewer operational challenges.

Access to equipment

THE PROBLEM: Drilling through a jacket involves many logistical steps. The handling of equipment during each phase, from pre-top side through to post top side, will considerably change. Thorough planning is needed to ensure access is available once all the necessary equipment is in place.

THE SOLUTION: The key to managing equipment logistics is to have the relevant drawings and documentation to hand that will show how the handling of equipment and other routine operations will be carried out once the top-side is in place. Well-timed workshops, drill well on papers (DWOP) and storyboards will further enhance the planning and help mitigate potential problems.

Batch drilling

THE PROBLEM: Batch drilling can create huge cost efficiencies; after all, nobody wants to pay for a rig to be sitting still. It can be challenging to keep a rig working but it can be achieved through detailed planning and a constant supply of equipment coming on board. Holding a conductor in place during cementing is one process which keeps a rig at a standstill.

THE SOLUTION: During a typical conductor installation process, a rig would be required to hold each conductor in place whilst the cement cures; this could be for anything between eight and 18 hours. This is where the Claxton conductor cement support system is a game changer and it does exactly what its name suggests. The tool greatly reduces the time required to batch-set conductors by holding the conductor whilst cement cures using a jack and clamp mechanism, allowing the rig to skid to the next slot and begin running the next conductor.

Cold cutting eliminates spark potential when cutting conductors and provides an accurate cut height, in various orientations, achieving a clean machined finish. With a 7”– 36” cutting range, this can be matched to the batch setting challenge for an optimal time-saving solution. Cold cutting equipment will need to be determined by well construction; piled conductors need to be a specified length and cold cutting can provide this accuracy.

Interface issues

THE PROBLEM: Connecting various pieces of equipment, including the platform and the rig, can be challenging. Poor interfaces can greatly affect fatigue performance, especially as tolerances build up, and these challenges will grow as jack-ups drill deeper. Issues can also arise when space-out plans are not adhered to, resulting in centralizers being placed incorrectly.

THE SOLUTION: An overshot system allows connection to plain end pipe with an anchor and seal. Installation is fast and simple compared with conventional methods, minimising shutdown time. A no-weld environment eliminates the need for cool-down periods and hot-work permits, enhancing the safety of operations. The overshot systems that Claxton provide are easily removable and reusable, therefore, can contribute to cost savings. The system also benefits from environmentally friendly controlled containment and draining of fluids and debris from the conductor.

Surface risers are more than just pipe; they offer a safe interface between platform and rig – continuing the conduit needed to join the conductor to the rig. Once handling issues have been identified and specifications confirmed through riser analysis, there are multiple auxiliary equipment configurations to ensure surface risers are adequate for every project.

Temporary decks

THE PROBLEM: A temporary deck will be required to undertake manned operations on a jacket before topsides are installed. The design and installation of a temporary deck can raise a variety of questions including; where is it held prior to and during the installation and how is it maneuvered into place? Can it be easily removed, or will it remain in place adequately interfacing with top side?

THE SOLUTION: The challenges associated with installing a temporary deck can be mitigated by combining the deck with the rig for sailing and installation. The original deck hatches must be removed during drilling operations, which usually leaves a deck opening of 2.5 square meters. Deck hatch covers can be used to ensure a safe working deck area around each well and can be used through all phases of drilling operations; open hole, running and operating HP riser and LP riser; through to completion.


These solutions are all available from Claxton and can be combined into a packaged integrated service. If you have any questions or would like to speak to one of our technical experts about how we can support your project, please get in touch. We can also cover any of the challenges and solutions in more detail in future blogs.

Click here to download Claxton’s drilling riser systems buyers guide

Topics: drilling risers, north sea, riser

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