Design concept for implementation of a novel subsea gas dehydration process for a gas/condensate well

• Subsea dehydration system successfully modelled for a medium sized gas-condensate well.
• Technical solution provides a high reliability solution with very low power requirements.
• The process modelled a viable solution for low subsea temperatures.

Natural Gas usually contains significant quantities of water vapour, which must be removed for gas processing and transmission. Common allowable water content of transmission gas ranges from 4 to 7 pounds per MMSCF (64–112 mg/m3). Failure to sufficiently reduce the water content can lead to condensation of liquid water and the formation and accumulation of gas hydrates into pipe blocking plugs. This is particularly important for subsea pipelines with the high pressure and low temperatures conditions that exposes the gas to hydrate formation conditions.To meet the demands of deeper and more remote reservoirs, subsea processing has been poised as one of the most potentially promising technology developments in the offshore development.A novel dehydration solution that is applicable for subsea installation has been designed and tested in the laboratories of Clean Gas Technology Australia department of Curtin University. The solution utilises the concepts of gas cooling through expansion and the controlled formation and management of gas hydrates to reduce the water content of a saturated gas stream to levels suitable for gas transport in subsea pipelines. The pilot plant implemented to test the solution design at pressures up to 10 MPa (1469 psi) and flow rates of 35 std m3/h (30 MSCFD) demonstrated that dehydration performance better than achieved with batch experiments was achievable.This paper describes a design methodology to migrate the process to a subsea implementation and presents a model for a production implementation using the experimentally obtained dehydration performance, demonstrating that it can provide a viable subsea dehydration solution.