Reducing Greenhouse Gas Emissions of Mobile Offshore Units; Pathway and Case Study Alternative Fuels for Self-Propelled Multipurpose Jack-Ups

Abstract The worldwide energy transition and greenhouse gas emission-reduction targets impact the offshore industry. The sector, as part of the maritime industry, is working to meet increasingly strict international and regional emission regulations through measures such as energy efficiency and alternative fuels. In this paper we describe the generic pathway to reduction of the operational emission of greenhouse gases for Mobile Offshore Units (MOUs). This is a relative new area of attention in the offshore sector. The paper provides an overview of monitoring and energy efficiency measures that are suitable for MOUs and their operations. In addition, it discusses applicable regulations and explores solutions for reducing greenhouse gas emissions and their impact on design of MOUs. Specifically, we have performed a fuel emissions and vessel design impact case study for a self-propelled jack-up with 1,500 t variable deck load for two typical operating profiles: making an accommodation service trip or a field move in the Middle East region. We compared the global warming contribution of the greenhouse gas emissions of the operation and the impact of fuel storage for five different types of fossil and e-fuels. This high level assessment of the greenhouse gas emissions is based on their contribution to global warming over a 100-year period. This is done for the well-to-wake emissions of the assessed fuel types. The case study assessment shows that fossil-based alternative fuels, such as gray methanol, gray ammonia or gray hydrogen are to be avoided as marine fuels: they create more greenhouse gas emissions than marine gas oil. It also shows that green (i.e. bio- and electro-) fuels can achieve a reduction of 79% or more in greenhouse gas emissions. The volume and weight impact of alternative fuels on the design of offshore installation vessels are included in the assessment. These findings can also be applied to other types of MOUs. By replacing a fossil fuel such as marine gas oil with green alternatives, the IMO emission-reduction target for 2040 is attainable. The IMO net-zero ambition for 2050 will require further development of energy carriers and energy conversion systems with net-zero well-to-wake emissions. The green alternative fuels come with challenges regarding the weight and volume for fuel storage. The energy transition timetable is driven by regulatory requirements and political choices, as well as by technological developments and the associated costs and rewards. The regional availability of alternative fuels and fuel supply infrastructure for the maritime and offshore sector also play an important role.