Nanotechnology for improved performance and lifetime of Direct Riser Tensioners

Direct Riser Tensioning system (DRT) are complex systems with multiple components affecting their performance. From a tribological perspective the complex interactions between the seal composition, rod alloys composition, the chemical interaction with the hydraulic fluids and the harsh environment in offshore (corrosive environment such as sea water and presence of abrasive particles such as mud particles) drastically reduces the DRT lifetime span. The goal of the NanoTribo project has been to better understand the interaction between all the components involved in the systems from atomistic to macroscopic scale. The knowledge generated in the frame of the project has been of special importance since the complex chemistry of the fluids (which normally includes different chemical components with specific purposes such as friction modifiers, thickeners, anti-foaming, anti-oxidants, pour point depressants, etc.) and how they interact with the moving surfaces (e.g.: rod and seals) strongly affects the performance of the systems. Based on the information gained during the first years of the project it has been possible to propose new materials and fluids combinations and propose new compositions for a better performance. Lab test results confirmed the better performance of the proposed solutions. Results have also been confirmed in a bigger scale. A Multi Degradation Lab Scale (MDLS) test rig which mimics the DRT system in a smaller scale was designed and built as part of the project. Testing in this rig confirmed lab test results. The main result is a new fluid with promising characteristics: Improved frictional and wear performance Compatibility with seawater environment Compatibility with all hydraulic cylinder components Do not cause sludge formation Keep constant viscosity over time Be environmentally friendly (i.e. the chemicals used are not harmful to the environment) Low cost of production All qualifying testing have been successfully performed.

I 2018 ble det jobbet med planer for kommersialisering av væsken. Gjennomført møter med NTNU/Sintef og Innovasjon Norge. I tillegg en patent søknad ble sendt i Oktober 2018 som er under behandling. Plan for å teste væsken som del av en offshore pilot i samarbeid med Odfjell Drilling ble lagt fram for ledelsen i NOV 13/12 2018. I forberedelsen, ble det laget bl.a kostnads beregninger og risikoanalyser NOV ledelsen besluttet at en offshore test ville være for dyrt. Gjenstående kvalifiserende tester skulle gjennomføres og samtaler for å lisensiere ut væsken til aktører i markedet påbegynnes. Fokus i 2019: 1. Direkte sammenlikning i testrigg hos NTNU av ny væske og gammel væske med kontrollert friksjon og temperatur påvirkning. 2. Test hos Trelleborg i Danmark og UK for å se hvordan pakninger reagerer mot den nye væsken. Væskeproduksjon og transport er belastet prosjektet. Testen dekkes av Trelleborg. Samtaler for videre lisensiering kjøres utenfor prosjekt.

Today many exploration wells are located at water depths of between 1500 and 3000 m, meaning equally long riser pipes have to be used. A drilling riser is fixed to the seabed, connecting the well to the drilling vessel acting as an extension of the drilli ng well from the seabed to the drilling vessel?s drillfloor. Direct riser tensioning (DRT) systems, consist of 6 large hydraulic cylinders (with a stroke length of 16 m) providing tensioning of the drilling riser while compensating for the drilling vessel heave movements. Direct Riser Tensioner (DRT) cylinders are complex tribological systems which include the use of seals, guide bands, hydraulic fluids/lubricants and materials in relative movement. These components fail due to the combined effect of mult idegradation processes (friction, wear, corrosion and mechanical stresses). The origins of these degradation mechanisms lie at the atomic level and cause enormous economical loses (down time can lead to lost revenues of more than USD 550,000 per day), saf ety consequences and potential environment impact Research is needed to fully understand the interaction of the elements of the tribological system at the atomistic level. This will enable the development of a unified model for friction, wear and lubricat ion processes which characterise the performance of the DRT cylinder. This research will lay a completely new foundation for the development of new-coatings and nano-based lubricants as central elements in DRT innovations. The complexity of such systems, needs a holistic approach including basic understanding of the processes occurring at the atomic level and also full scale tests. This project will establish a unified approach by developing advanced coatings on the Direct Riser Tensioning (DRT) rod surf ace that, combined with the seals and guide bands, catalyze the formation of a thin solid tribofilm by promoting the reaction with a nano-modified fluid