Gas developments are required to facilitate energy transition from carbon intensive energy to a sustainable balance of green and blue energy. The next decade will focus on exploiting gas fields globally to support this. A significant number of these fields are located in deepwater and /or are long distances from existing gas processing / LNG plants.

Transporting large volumes of gas from remote gas fields over longer distances and in deeper waters remains technologically and economically challenging. Conventional and near-term development options include subsea compression, floating vessels with topside compression and pipeline tie-back to shore, or floating liquefied natural gas vessels.

This paper and study are supported by The Oil & Gas Technology Centre (OGTC) and UK Oil and Gas Authority. It examines development options for a 200 km long 1700 m water depth tie back using integrated production modeling linked to power demands, along with installed steel tonnages. The Scope 1 and 2 emissions per unit of gas produced are analysed via a life cycle assessment using ISO 14044 as guidance for a long-distance gas tieback to the point of sale (inclusive of processing to sales specification). The major power intensive equipment used to develop these fields will be presented showing their proportion of the power consumption compared with the total; these include compression either onshore, offshore or subsea as well as the efficiency of the power generation devices in these environments. The paper will highlight the economics of each option and how varying the carbon price changes the commercial position of each option. The paper will show that by understanding what drives emissions, and how emissions relate to the amount of gas produced, that concept selection can drive upwards of 50% reduction in life cycle carbon emissions whilst improving project economic performance.

This paper examines multiple innovative technologies, providing technology readiness of new concepts based on the benchmarked study focusing both economic and carbon emission aspects. Finally, the paper will show that better economic outcomes with the decarbonisation of gas gathering systems is technically possible and can be deployed subsea to help meet the energy transition and allow the development of remote and deeper gas fields.

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