European Marine Energy Centre

Marine habitats are being targeted for the extraction of offshore renewable energy (ORE) as part of the drive to decarbonise electricity generation. Unmanaged biofouling impacts ORE devices and infrastructure by elevating drag forces, increasing weight, and accelerating corrosion, leading to decreased performance and survivability, and extending costly periods of maintenance. ORE deployments in high tidal flow locations are providing opportunities to study the biofouling unique to these habitats. In this study, surveys of numerous devices and associated infrastructure deployed at the European Marine Energy Centre in Scotland identified high tidal flow fouling assemblages. Substrate orientation relative to tidal flow appears to affect the abundance of key fouling species, including the massive barnacle Chirona hameri. This species is shown to recruit to a wide range of artificial substrates, over a prolonged period from mid-spring to mid-summer, and in maximum current speeds from 0.4–4.0 m/s. For the first time, C. hameri is reported in near-surface depths, on uncoated components of a floating tidal device. The highly gregarious settlement behaviour and rapid growth exhibited by this species may have important implications for managing fouling in the ORE industry, especially in ‘niche’ areas. Anti-fouling strategies and maintenance scheduling applicable to ORE and other marine industries are discussed.

Tidal energy resource characterisation using acoustic velocimetry sensors mounted on the seabed informs developers of the location and performance of a tidal energy converter (TEC). This work studies the consequences of miscalculating the established flow direction, i.e., the direction of assumed maximum energy yield. Considering data only above the proposed TEC cut-in velocities showed a difference in the estimated flow direction of up to 4°. Using a power weighted rotor average (PWRA) method to obtain the established flow direction resulted in a difference of less than 1° compared with the hub-height estimate. This study then analysed the impact of turbine alignment on annual energy production (AEP) estimates for a non-yawing tidal turbine. Three variants of horizontal axis tidal turbines, which operate in different locations of the water column, were examined; one using measured data, and the other two via modelled through power curves. During perfect alignment to the established flow direction, natural variations in flow meant that the estimate of AEP differed by up to 1.1% from the theoretical maximum of a fully yawed turbine. In the case of misalignment from the established flow direction, the difference in AEP increased. For a 15° misalignment, the AEP differed by up to 13%. These results quantify important uncertainties in tidal energy site design and performance assessment.

A novel system was developed to deploy settlement panels to monitor biofouling growth in situ and evaluate antifouling coatings at depths representative of operational conditions of full-scale marine renewable energy devices. Biofouling loading, species diversity, and succession were assessed at depths ranging from 25-40 m at four tests sites in Orkney (UK) featuring extreme wave and tidal current exposure to more sheltered conditions. Evaluations were carried out over a period of 8 months with intermediate retrieval of samples after 3 months. Early pioneer fouling communities, comprised of colonial hydroids, were succeeded by tube-forming amphipods across sites while solitary tunicates dominated in greater shelter. The highest biofouling loading was observed on high-density polyethylene (HDPE) panels (6.17 kg m−2) compared with coated steel (3.34 kg m−2) panels after 8 months. Distinct assemblages were present at exposed vs sheltered sites. Better understanding of fouling and antifouling strategies may provide guidance to more effectively manage biofouling impacts in this sector.

The Orkney Islands, situated off the north off Scotland, have an abundance of renewable energy resources, and already produce over 100% of average annual electricity demand year on year. The current grid, which was built to bring electricity to the islands rather than export it to the mainland, is now very congested with green electricity. Therefore, innovative projects are being developed to use Orkney's energy in different ways to try and circumvent these shortcomings with Orkney's branch of the national grid. The European Marine Energy Centre (EMEC) is at the leading edge of harvesting energy from the waves and tides and is now turning to the production of green hydrogen through electrolysis as an alternative energy export vector. This article explains why it is seeking to export energy harvested from the tides as a gas rather than electricity and outlines some of the opportunities this approach may offer.

Abstract This paper describes the benefits and lessons learned from drilling 44 deep gas reservoir sections with sodium and potassium formate brine drilling fluids in Saudi Arabia's prolific Ghawar field from 2004 through 2008. Initially in Saudi Aramco, the formate brine drilling fluids were used primarily to prevent formation damage across the pre-Khuff sandstone reservoirs. As formate use burgeoned, their ancillary benefits such as stuck pipe mitigation, better bit performance, better than expected reservoir performance, lower pump pressures, torque and drag, solids content and enhanced temperature stability; use as a completion fluid and recyclability became evident. The fluids have been used in a variety of reservoir drill-in fluid applications in the pre-Khuff, Jauf and Unayzah sandstones with bottom hole temperatures (BHT) up to 323°F. The formates have also been used by Saudi Aramco in the Khuff carbonates for single and dual lateral horizontal wells where the drilling fluid overbalance to formation pressure sometimes exceeds 1,400 psi. In addition to the return permeability testing conducted prior to actually drilling the first wells with formates, the fluids nondamaging properties were proved up in the case of the Tinat-A well, a Unayzah-A re-entry/horizontal sidetrack, that had to be shut in for three years, due to a mechanical obstruction in the completion, with a 90 pounds per cubic foot (pcf) sodium/potassium formate completion fluid left in the hole as kill fluid. After removing the obstruction via a snubbing unit workover the well initially tested at 30 mmscfd with 4,320 psig FWHP, which was much higher than estimated. In a JFYN Unayzah B/C well, JFYN-A, only 1,214 ft of 5-7/8?? hole was cut across the reservoir using a recycled 92 pcf potassium formate and the well flowed back at 45 mmscfd with 358 bopd oil on a 44/64?? choke, which was also much higher than expected. Laboratory return permeability to gas test with Khuff-C cores showed 91% return permeability after flowing through the cores with potassium formate drilling fluid with 2% commercial lubricant as compared to 40% return permeability for the KCl Polymer drilling fluids of the same density normally used across the Khuff-C. The formates have also been used in combination with fine, medium and coarse calcium carbonate functioning as a bridging agent to drill in extreme overbalance situations across the Khuff-C reservoirs. The best example of this practice is UTMN-J, a Khuff-B re-entry sidetrack, where an 81 pcf sodium formate brine served as the base drilling fluid to drill and complete the 3675 ft horizontal section. The well was flowed back at a rate of 35 mmscfd without enzyme treatment or acid stimulation.

Attempts to convert wave energy are not new: wave energy conversion began with the purpose of signalling the presence of navigation buoys. Wave energy was used to force air up through the central channel of the buoys which contained integral whistles to give an acoustic warning. This application was developed in the 1940s, with generators used to light the buoys. Later work in the 1970s in Norway and the UK (Salter’s Duck), although not progressed to commercial levels, saw the first real precursors of today’s electricity generating converters based on wave power. In contrast to today’s more stringent regulatory requirements, these early wave energy devices were not subject to licensing constraints or assessments of their impacts. So, although the capture and exploitation of wave power for human use is not new, the associated studies into the possible environmental impacts of this in-dustry are now key elements of its future success. It has been stated that wave energy schemes produce no emissions in normal operation (Thorpe, 2001), which is true with regard to emissions typical of fossil fuel exploitation. However, there are other possible emissions covering both the operational phase and the associated installation, maintenance and decommissioning phases. During the operational phase there is likely to be noise emitted by devices under operation, a risk of emissions associated with any incidents involving pollutants (e.g., hydraulic oils), emissions from antifouling coatings, and so on. Like all the other renewable energies, wave energy will inevitably have some effects on the environment, positive as well as negative.