Kieran Kavanagh of Wood Group Kenny
Kieran Kavanagh
With 28 years of experience in offshore and marine engineering, specialising in riser and subsea engineering, Kieran of Wood Group Kenny has managed several technology projects and JIPs and has authored extensively in riser and related technologies. He has been a member of the joint API/ISO task groups developing new codes of practice for flexible pipes, drilling risers and floating production risers.

Don’t underdesign or overdesign Overdesign can be as problematic as underdesign in some cases. In order to ensure that both engineering and commercial criteria are satisfied, simulation and modelling are key tools. At a fundamental level, everything that is designed for deployment in the offshore environment is modelled in some way to ensure that it is compliant to code and fit-for-purpose. More often than not, the modelling is carried out entirely in the digital domain if the properties of the materials being used are well known

Simulation is slightly different in that it is used to analyse a ‘what if’ situation where a certain set of conditions are applied to a structure, component or vessel. Very often simulation takes verified data and extrapolates it to mimic conditions that cannot easily be tested because of operational considerations or the magnitude of the loadings involved.

Applying real-time data Loadings need not be theoretical: Wood Group Kenny’s OPTIMA model for offshore drilling, completion and work-over vessels combines both a structural model and environmental conditions measured in real- time to analyse the structural response of the riser. By using actual data rather than theoretical or assumed data, it is possible to work in a wider range of conditions while remaining within the operational limits of the riser. As well as working ‘online’, taking data directly from an event, it is possible to simulate an event that has not been measured directly. Deep water drilling vessels have a finite positioning envelope relative to the riser. At any time, the crew needs to be aware how a failure might cause a drift off (driven by wind, wave and currents) or a drive-off (where powered thrusters are pushing the vessel in a direction that was never intended) and how long they have to react before suspending operations and disconnecting the riser in time to prevent damage. Historically, up to around ten years ago, the drift off path would be calculated as a theoretical exercise using the worst case scenario of wave, wind and current all on a co-linear heading. This methodology would

predict an onerous drift-off path with the crew having to disconnect the riser sooner, under lesser environmental conditions than were strictly necessary. By applying the simulation driven by real-time metocean data, a far more accurate time to disconnect can be calculated while still maintaining all the safety factors.

With costs that can run close to a million dollars per day, the greater uptime generated by using the simulation can be commercially significant. The savings might be even greater than just the additional time gained before disconnect, as some disconnect events might not be required at all: the redundant time waiting for the environmental conditions to calm down and then reconnecting the riser could be replaced by productive uptime. By working with real information in real time there are fewer uncertainties and far greater confidence in the system.

Understanding and managing pipelines though modelling The same confidence can be brought to managing flow conditions and structural response in pipelines. Wood Group Kenny’s flow assurance and process modelling teams work with operators to understand how different events might affect the operation of a pipeline system. Keeping a pipeline system free of hydrates or waxing that could shut down production is key throughout the life of a system. By simulating crucial events such as the start-up of a well, steady state production, the long-term production profile from the start until the end of field life, or shut down conditions, it is possible to pre-empt issues and mitigate accordingly. It is possible to calculate the ‘no-touch’ time before an operator needs to circulate methanol to stop hydrates forming and blocking pipes when an offshore production system shuts down. This also feeds into the amount of insulation that pipes need and any requirements for active heating technologies in combination with operational temperatures and pressures that are required to ensure that hydrates or wax do not form anywhere in the subsea pipeline infrastructure.

Taking process modelling to the next level, it is now possible to model a whole subsea system in order to understand how the whole oilfield ecosystem works under different operating conditions and scenarios. In some cases, online modelling of a pipeline is done because the impact of one shutdown, or even a shortfall, can be in the millions of dollars when some of these networks are transporting more than one million dollars of product per hour. It is important to know how an event such as the start-up of a well will impact on the infrastructure elsewhere in the system. Simulations can help calculate pressures, temperatures and production profile all along the pipeline system leading to a production unit, how they vary with time and what the operator has to do to maintain flow in that well. By feeding in real-time data it is possible to simulate ‘what if’ scenarios and mitigate accordingly. This is particularly useful in the early days of operation where office based calculations with some conservative inputs can be revisited for more efficient and economic operations.

The need to calibrate and validate There is an onus on engineers and technologists to make sure that only reliable technology is deployed and that it is qualified before it is deployed offshore. The qualification and validation process relies on partial, prototype or full-scale testing to prove that the system is both accurate and robust. By adding effective real-time measurement into the mix, it is possible to calibrate and validate modelling and simulation systems far more accurately.

It is important to recognise that the evolution towards technology change and the willingness to promote and accept new systems can add value to any business working in the offshore environment. There is a fundamental choice as to whether operators carry on following the same processes or invest in technology to work efficiently and in a way that either makes or saves their business time or money. Certainly from both a technology and a commercial standpoint there are big gains to be made by leveraging the best simulation and modelling technology on offer.