Can an offshore drilling rig run on green methanol?

Noble Corporation recently concluded a conceptual study for conversion of offshore rigs to green methanol. The effort, detailed in this article, is part of the firm’s quest for decarbonization in the offshore sector.  

Rising demand for low-carbon fuels. The offshore and international shipping sectors use oil-based fuels to power most of the vessels in the world today. Ambitions to lower emissions are increasing, as the global commodity demand rises.  

The International Maritime Organization (IMO) set expectations to reduce 20% to 30% of greenhouse gas (GHG) emissions by 2030 to drive their 2050 net-zero scenario, Fig. 1. The offshore industry seeks decarbonization solutions to meet the emerging regulatory framework from IMO, rising commodity demand for larger energy consumption, and the need for scaling up low-carbon technologies.  

Fig. 1. A timeline of regulatory action already taken, and anticipated action needed, to address climate change by 2050. Source: The International Maritime Organization.

Cutting carbon dioxide by up to 95%. Adoption of low-carbon technologies will involve a combination of retrofitting existing assets and building new assets to replace aging units over time. Given long vessel and rig lifetimes, innovation is critical in the development of the right designs and near-term technologies while the corresponding supply chains become established. In the shipping space, it is possible to retrofit existing engines, based on several fuel options which are shown in Table 1.  

Based on Table 1, the market will evolve through a combination of different scenarios. Regardless of the situation, green or renewable methanol plays a critical role in cutting carbon dioxide emissions, as compared to conventional fuels (oil and LNG). The Methanol Institute estimates renewable methanol can cut carbon dioxide emissions by up to 95%, reduce nitrogen oxide by up to 80%, and eliminate sulfur oxide and particulate matter emissions.  

Innovating as a leading offshore driller. In the pursuit of sustainable energy solutions and reducing environmental impact, Noble decided to further explore the use of green methanol, a renewable fuel that holds immense potential for decarbonizing offshore operations.  

The process began with the question, “Is it possible to introduce methanol onboard a drilling rig, from a safety, operational and feasibility perspective?” Noble began to answer this question by conducting a feasibility study on the upgrade of a harsh environment jackup rig in the Norwegian sector, emphasizing the integration of green methanol as a key component in the transition towards a greener future, Fig. 2. 

Fig. 2. An illustration of Noble Corporation’s upgraded green methanol drilling rig.

In conceptualizing the revolutionary green methanol design concept, Noble estimated potential carbon dioxide savings of up to 80% to 90%, depending on several operational factors. 

Designing a green methanol drilling rig. The first step was an investigation into the regulatory landscape relevant to alternative fuels used on an offshore rig, and offshore operations in general.  

Initial meetings were held with key stakeholders, such as Class, Flag State authorities, and various local regulatory bodies. Discussions centered on the feasibility of integrating methanol into rig operations, and an understanding of necessary deviations from established maritime sector protocol.  

All parties expressed strong interest in the concept, and the project was met with positivity in this very early phase. The conclusion was that the concept would be possible and, in general, the existing guidelines and regulations from Class and IMO would apply. 

Subsequently, Noble proceeded with a deep dive into the design and modification needed for the inclusion of methanol aboard a jackup rig operating in Norway. Together with an established design consultancy, the company explored the technical and logistical aspects of such an upgrade, incorporating experience from other methanol projects in the maritime sector. 

Key to the feasibility study was the replacement of all four engines with new engines capable of running efficiently on methanol. Additionally, the design and installation of state-of-the-art methanol storage tanks and piping systems would be crucial to limiting impact on the rig and ensuring seamless integration. 

Engine technology. Power plants onboard rigs are integral to safe operations. Engines are commonly run at lower loads to enable sufficient reserve when needed for higher peak loads. This variation in load can pose a challenge, due to the characteristics of alternative fuels. Noble’s hybrid rigs already have energy storage systems installed, enabling more efficient engine operation, including optimized use of waste energy from top-side drilling systems. 

Recently, the technology for methanol engines has developed at a rapid pace. Several of the major vendors in the market today have engines that can provide seamless fuel changes between methanol and diesel. Fuel flexibility is key, but it can also be constrained by supply chain issues. 

Rig engines use diesel pilot fuel to allow the combustion of methanol. Keeping diesel use to a minimum is necessary to affect significant emission reduction. Pilot fuel can easily be substituted with biodiesel (HVO), enabling maximum emission reductions from the rig. Due to the increased cost of HVO, it is preferable to have as high a methanol share as possible.  

Converting existing engines to methanol operation would not be possible; therefore, the feasibility study had to consider a complete exchange of the rig’s engines for new ones. The new engines would have to be capable of running efficiently on both methanol and diesel, to ensure an optimal solution for the rig in all operational scenarios.  

Due to the requirement for continuous operation, engine performance must be unaffected in both diesel and methanol modes. Several engine vendors offer methanol-ready engines, and the methanol rig design project has received significant technical support from this segment of the industry. 

Tanks. A crucial challenge to introducing methanol as a rig fuel source is its lower density, resulting in the need for more than double the comparable volume of diesel. For the engines to run in both methanol and diesel mode, the tanks would need to accommodate both fuels while adhering to regulatory design requirements for barriers, cofferdams and venting systems. Therefore, the feasibility study involved the design and installation of advanced methanol storage tanks, piping and double-walled piping systems.  

During the process, Noble evaluated many different designs and developed an innovative solution tailored to minimize the impact and installation time, combined with optimum utilization of the rig design and available space onboard. 

Operational assessment. The use of an additional green fuel will impact the rig design, due primarily to the additional weight of the methanol engines, tank and related equipment. Accordingly, the feasibility study also assessed the impact of additional weight on the rig’s variable deck load capacity and the ability to perform maximum preload scenarios in challenging locations. Accommodation of the additional weight can be achieved by optimizing inventory management, drilling equipment and other liquids onboard.  

Outcome. The feasibility study yielded several interesting findings: 

1. It is possible to upgrade a rig to enable green methanol usage. 
2. It’s also clear that such a conversion comes with a considerable investment. 
3. There is more progress to be made in ensuring a reliable supply of green methanol. 

The conceptual design offers the option to use green methanol, fossil methanol, conventional diesel and biodiesel, which maximizes fuel flexibility and the associated emission reductions after such a conversion.  

Through the integration of green methanol into offshore operations, stakeholders can reduce their environmental footprint and contribute to the broader goals of energy transition and decarbonization programs. Moving forward, continued investment and innovation in green technologies will be essential for realizing a more sustainable future for offshore operations. 

Noble’s perspective on sustainability. Noble has adopted a 360^o decarbonization strategy, based on three pillars:  

1. Data and technical upgrades,  
2. Sustainable operations, 
3. Customer collaboration 

The technical experts, comprising Noble’s Decarbonization Solutions and Innovation team, lead the company’s decarbonization efforts, sustainability strategy and emission reduction targets. They work within a range of solutions encompassing energy efficiency upgrades, energy management plans, data analytics, testing of alternative fuels, and innovative solutions to reduce GHG emissions in the offshore industry. 

Noble has extensive experience with shore power, hybridization, selective catalytic reduction, energy efficiency software, and sustainable biofuels (e.g., HVO/renewable diesel). In pursuit of decarbonization, these solutions provide significant optimization potential; however, it is also clear that the only way to fully decarbonize the offshore sector is to explore onboard fuel sources that offer a carbon-neutral or zero-emission alternative.  

ALTERNATIVE FUELS – AN OVERVIEW 

The maritime industry is actively exploring the use of alternative green fuels, both for newbuilds and retrofit solutions, driven largely by the regulatory landscape. When discussing alternative fuels, it is important to differentiate between zero-emission fuels and carbon-neutral fuels. 

Below is a brief overview of the key alternative green fuels shaping the future of the maritime sector: 

Biofuels. When biofuels are made from renewable biomass sources, biodiesel and bioethanol offer sustainable options. One of the main advantages is that they can be blended with conventional marine fuels or used independently.  

Due to the need for sustainable feedstock, they often come with a significant price tag, as well as potential supply issues. Biofuels may offer carbon neutrality, based on their feedstock. 

Liquefied natural gas (LNG). LNG is considered a transition fuel, and there is currently no expectation that green LNG will emerge as the fuel of the future. There are inherent challenges to storing LNG; however, engine technology is readily available. Retrofitting for LNG use requires specialized engines and fuel storage. 

Hydrogen is a zero-emission fuel that produces only water vapor and heat during combustion. Use of pure hydrogen is a challenge, due to its low density, which makes safety, storage and utilization difficult. However, green hydrogen is a key component of any alternative fuel of the future. 

Ammonia. The development of ammonia as a carbon-free fuel, produced through renewable energy-powered electrolysis, is also on the rise. However, there are still challenges to overcome before ammonia can be a viable alternative in marine applications.  

Obstacles include significant safety considerations, storage and infrastructure shortcomings. Combustion of ammonia in engines is still under research, as its ignition properties are challenging. 

Green methanol is the predominant green fuel, due to its advantageous properties, which include easy storage and handling at ambient conditions, the highest energy density of the alternatives, and good combustion properties requiring small amounts of pilot fuel.  

When produced from renewable sources like biomass and renewable hydrogen, green methanol offers lower emissions and carbon neutrality. Several engine vendors already offer well-proven engines capable of operating on methanol and diesel with comparable performance characteristics. This is surely needed in offshore applications, where low average loads and high-power fluctuations are inherent conditions in drilling operations.