News 16 Oct, 2023

Green Gas Stations in the Gulf - Waypoints 05

Repurposing the Gulf of Mexico’s life-expired oil and gas platforms for renewable energy could one day see them serving as hydrogen refuelling stops, writes UH Energy’s Ram Seetharam. 

Dr. Ram Seetharam
Repurposing Program Lead (UH Energy)

Like many offshore oil and gas production areas around the world, the Gulf of Mexico is dotted with hundreds of giant steel platforms that have reached or will soon reach the end of their useful lives. In June this year there were 1,533 platform structures sitting on the outer continental shelf and the owners of 356 of them had submitted applications for decommissioning.

Decommissioning production platforms is a hazardous and expensive task, involving dismantling and removing the topsides, deck, jacket, foundations and delivery pipeline – all while taking great care to avoid any spillage of hydrocarbons. UH Energy – the University of Houston’s energy centre where I am Repurposing Program Lead – is looking at how these platforms could be adapted for reuse in new green energy infrastructure. Funded by the US Department of Treasury’s RESTORE Act1, UH Energy recently finished the first phase of a joint industry-government-public-academia collaboration on repurposing offshore infrastructure for clean energy (ROICE).

Our starting points were to look at the Gulf of Mexico’s potential for wind power development and the geospatial distribution of existing offshore platforms and pipelines. We found that average wind speed in the Gulf is around 7−9 m/s, which is more than adequate for wind power generation. 

Based on standard 15 MW horizontal-axis turbines supported on monopiles or floating foundations, we estimated the levelized cost of energy – that is total discounted life-cycle cost of the generation divided by total energy output − for a 29-turbine windfarm was in the range of US$100−$226/MWh. While significantly more than the US$24−75 estimate for onshore wind, this is not dissimilar to the US$105–150/MWh reported for the North Sea 2.

So where do the old production platforms come in?

We see two options for repurposing these in wind-power developments. The first is as an offshore substation, which is directly connected to the turbines and then raises the voltage (typically from 33 kV to 150 kV AC) to transfer power to the shore grid via a new undersea cable. The second, more radical, option is for the platform to become an offshore hydrogen production plant. This uses the windgenerated electricity to desalinate seawater and split it in an electrolyser into hydrogen and oxygen. The oxygen is vented to atmosphere and the hydrogen flows ashore via the existing oil or gas pipeline. We estimate that a 435 MW 29-turbine array could generate around 32 Mt/year of ‘green’ hydrogen. 

The wind-to-hydrogen concept is not new and is already being extensively trialled around Europe. In particular I recommend readers refer to the Sealhyfe project in France, the Deep Purple pilot in Norway, the Poshydon pilot in the Netherlands and the Behyond project in Portugal. However, none of these is specifically looking at repurposing existing oil and gas platforms to support the hydrogen plant. The main advantages of the wind-tohydrogen repurposing option over the windto-electricity one are that no expensive new shore connection is required, saving around US$2 million/km for power cables and US$0.8 million/km for pipelines. Furthermore, the hydrogen produced will be the sought-after ‘green’ version (that is with no greenhouse gas emissions), having been produced from only water and wind.


Estimated levelised cost reductions increase with water depth


Of course, there are many issues and challenges to overcome with implementing either of these options. The first is that the topside of the existing platform will still need to be lifted off and replaced with a new topside unit containing either a substation or hydrogen plant. However, topside removal is already factored into platform decommissioning costs and the repurposing allows the rest of the decommissioning process to be deferred for many years. 

The structural condition and safety of the existing jacket and deck will also need to be carefully checked and recertified for their new roles, as will that of the existing pipeline for the hydrogen option. Typically made from 150−600 mm diameter steel, these pipelines are not ideal for containing tiny hydrogen atoms. But the relatively low operating pressures of around 30 bar will be well within their rated capacity. Other solutions to possible leakage or ‘hydrogen embrittlement’ include copper-coating the inside, inserting a composite lining or mixing the hydrogen with natural gas. 

As to the cost saving from repurposing existing platforms, our initial estimates indicate that these start to become significant as the water gets deeper. For example, for a 415 MW 29-turbine wind-to-hydrogen system in 1000 m deep water, we estimate the complete levelized energy cost saving will be 24% if an existing platform is reused. For a smaller 105 MW seven-turbine wind-to-hydrogen system, the same saving will be achieved in just 250 m of water due to the reused platform saving making up a greater fraction of the total cost. The same sized wind-to-electricity systems offer a slightly lower saving due to the extra cost of the new shore cables. 

Moving forward, we have selected around 100 existing platforms in the Gulf of Mexico for further investigation in phase two of the research, with a view to identifying one or more commercial-scale demonstration projects. In parallel, ROICE has set up seven workshops to investigate specific regulatory, commercial and technical perspectives, and these are due to report back in early 2024. 

We now have over 50 members and supporters from various parts of the industry on board, including energy companies, operators, hydrogen specialists, classification societies and consulting engineers. We would of course welcome additional input from West P&I Club members, particularly those with expertise in offshore operations, risk management and re-certification.

Ultimately the aim is to quantify the cost-benefit of repurposing life-expired production platforms for clean energy, which in turn will enable us to determine how much regulatory support is needed to make such schemes attractive to investors and purchasers alike. While there is a clear demand for green energy ashore, there is likely to be increasing demand from the maritime sector, perhaps initially from hydrogen-powered support vessels and later from ships running on hydrogen-rich fuels such as ammonia. 

With sufficient storage, repurposed oil and gas production platforms could well become the green refuelling stations of the future. 

(Above) Graphic from Siemens Gamesa.
Waypoints Issue 05

Waypoints Issue 05

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