written by Tim Highfield & Tim Stringer
Published in Petroleum Economists’ June 2018 issue and republished here with permission.
After many years of anticipation, Floating LNG has become a reality. Nearly all the FLNG vessels currently operating, or under construction, are ship-shaped and destined for offshore, over-field locations.
Barge based LNG (BLNG), however, is focused on nearshore positioning where LNG facilities are mounted on a simple floating substructure and moored nearshore. The balance of the system (pre-processing, liquids handling, storage etc.) are decoupled from the liquefaction technology and can be in separate locations, if beneficial, an example being an FPSO in the deepwater over-field.
BLNG concepts typically comprise multiple LNG trains which, in aggregate, meet the required throughput. BLNG minimises project risk by better aligning the phasing of the development with the proving up of the reservoirs. It could also help to deliver greater certainty, through better control over the scope of supply and construction away from remote low infrastructure locations, according to io oil & gas consulting (io), a London based field development consultancy.
io presents the following top ten benefits of BLNG that explain its increasing popularity as a gas monetisation concept:
Technical
Modular trains. This offers a “design one, build many” philosophy enabling a more efficient production line or “factory” approach to fabrication.
Production flexibility. A multiple module LNG train configuration enables liquefaction to closely and efficiently match gas production rates. Smaller LNG trains have faster start-up/re-start times than world-scale LNG trains. As areas of the reservoir are proven up, additional trains can be more easily sanctioned and added.
Safety. Separating the liquefaction from the other processes and LNG storage with a “walk to work” philosophy is a safer alternative to the large FLNG vessels. The living quarters could be further separated along a jetty on another barge, jack-up or onshore.
Electrification opportunities. Nearshore BLNG may be able to achieve a lower carbon footprint by utilising (a degree of) power from shore (e.g. from a hydroelectric system or other renewable source), which ultimately increases uptime, availability and enables more gas to be sold to the end user.
Commercial
High availability. With multiple small LNG trains the reduction in export capacity during planned or unplanned shutdowns is limited to only the capacity of a single train (i.e. gas turbine maintenance) and not the whole facility’s output.
Easily expandable. A facility’s capacity can easily be increased by additional barges and contractible in late field life, as the field moves off plateau.
Strategic
Lower risk construction. BLNG construction, fabrication and pre-commissioning can be performed in a dedicated yard rather than at a remote site. A controlled environment with an already skilled workforce in place, is advantageous versus a local hire and train policy, and in addition a significant number of fabrication yards are in free zones, with low or no import duties.
Separate floating LNG storage. This is provided in a separate carrier moored alongside and not in the barge hull. This decouples the facility from the storage volume, similar to onshore LNG and eliminates a potential critical path from the schedule. In addition, if financing is a consideration, utilising LNG carriers may introduce leasing as an option for this element of the plant.
Simple transportation. The complete BLNG facility, fully fabricated and pre-commissioned can be transported as a single unit by a semi-submersible heavy transport vessel; as proven by Statoil on the Snøhvit development.
Reuse or decommissioning. BLNG is well suited to stranded gas as the barge is more mobile and amenable to relocating elsewhere for a new gas stream. Decommissioning is simplified, and environmental risks are reduced compared to in-situ decommissioning.