This paper will look at the technical, strategic and commercial benefits of Barge Liquified Natural Gas (BLNG) technology in Deepwater and Onshore gas developments.
The majority of the Floating Liquified Natural Gas (FLNG) vessels currently operating are ship-shaped and destined for offshore, over-field locations. However, this approach does not necessarily offer the optimised solution for gas monetisation from Deepwater gas field. Equally where there is an abundant source of onshore gas, onshore LNG liquefaction plants have generally been selected, e.g. on the US Gulf Coast, this may also not be an optimised solution.
An alternative solution in both these situations is BLNG, focused on nearshore positioning with LNG facilities mounted on a simple floating or grounded substructure with the balance of the systems (pre-processing, liquids handling, possibly storage etc.) decoupled from the liquefaction technology and in a separate location, such as a Central Processing Facility (CPF) FPSO in the deepwater or a gas processing facility near the development wells onshore. It is recognized that positioning the gas treatment facilities close to the wells normally enhances the overall recovery from the reservoirs as a lower back pressure can be achieved and gas compression added as required.
An example of an overall field development scheme utilizing a nearshore BLNG plant with a deepwater FPSO CPF and a Liquified Natural Gas Carrier (LNGC) for storage is shown in
BLNG Field Layout Solution for deepwater gas
This paper addresses the following benefits of BLNG and why it's becoming increasingly viable as a gas monetization concept.
Potential risk reduction benefits in both the operating and construction phases.
Offers a "design one, build many" philosophy enabling a more efficient production line or "factory" approach to fabrication.
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.
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 or a more efficient traditional solution), which ultimately increases safety, availability and enables more gas to be sold to the end user.
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 engine maintenance or exchange) and not the whole facility's output.
A facility's capacity can easily be increased by additional barges and contractible in late field life, as the field moves off plateau.
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.
Potential for separate floating LNG storage being 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.
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 the potential environmental impacts are reduced compared to in-situ decommissioning.
Finally, the paper will address a more certain approach to the selection of a BLNG solution where the optimum gas monetisation solution is identified in the concept phase front-end loading (FEL 1) of a project.