In many offshore oil and gas fields, gas is injected into the reservoir for production support or disposal. Hydrocarbons travel from production wells to a topside processing facility, where gas is separated and compressed before flowing to injection wells. This requires substantial processing space, weight, power, and pipe infrastructure. Gas reinjection can be energy and emission intensive, in addition to posing limitations on throughput capacity.
Reinjecting gas subsea is an alternative approach to the traditional topside method. With modern processing technologies, the full reinjection process occurs subsea; gas does not need to travel to an intermediate topside facility and then back again.
Subsea gas reinjection is ideal for extending production plateau, debottlenecking topside facilities, and decreasing emissions of gas-constrained greenfield or brownfield developments. By boosting liquids to the facility, production can be accelerated, and the accumulated production increased.
Additional benefits include improved safety and reliability, reduced topsides space and weight, reduced power demand, and reduced pipe infrastructure. This paper discusses the selection of the novel subsea gas reinjection concept, its benefits, engineering challenges, and special design considerations.
The arrangement for subsea gas reinjection is flexible, depending on its application. It combines subsea separation and subsea boosting. While subsea compressors may seem ideal, this paper describes repurposing traditional subsea single phase pumps for injecting dense phase gas. Single phase pumps have been used for liquid boosting for years; gas in dense phase behaves as a liquid. Compared to compression systems, subsea pumps are preferred as they present lower complexity and cost.