Project integrated LNG offloading availability assessment for FLNG

The process of undertaking a techno-commercial viability assessment of a Floating LNG—taking into consideration offloading availability at its core—is presented in this extended abstract which evaluates using a combined heuristic, analytical and probabilistic approach. This approach, when combined with project commercial drivers, is folded into an uptime assessment to forecast the project-integrated techno-commercial performance of the terminal.

This process has been developed within INTECSEA in the last six years and has been applied to FLNG facilities around the world. It can be applied to floating liquefaction plants which export LNG (FLNG) and floating regasification units (FSRU) importing LNG and takes into consideration side-by-side, tandem, ship-to-jetty and jetty-to-ship loading and unloading. The extended abstract deals specifically with side-by-side loading.

The uptime assessment forecast enables terminal owners and/or operators to be confident of the LNG throughput that can be achieved, the facility’s configuration, storage size, offloading technology and location and capital and operational expenditures (CAPEX and OPEX) is optimised. The forecast assesses the contractual viability for LNG off-takers and suppliers. The forecast is the key to terminal export and import performance guarantees.

To forecast uptime and terminal performance a time domain simulation is performed. The analysis takes into account terminal storage size, configuration and operational philosophies, site-specific historical hindcast metocean conditions (wind, wave and current), logistic chain data, operator experience and the human factors that drive operational decision-making.

There are three key parameters for a viable floating LNG export/import terminal and they are the key contributors to terminal techno-commercial performance:

1. LNG loading/unloading availability;

2. Gas production/send-out availability; and,

3. LNG supplies and sales agreements.

Loading availability (LNG export) refers to the time it takes to offload an FLNG to an LNG Carrier (LNGC). Unloading availability (LNG import) is the time it takes to offload an LNGC to an FSRU. This is critical to ensure that LNGCs can berth and load/unload LNG at scheduled times with minimal delays.

Gas production availability is the time it takes for gas to be processed, liquefied and stored on an FLNG. Gas send-out availability is the time in which LNG can be regasified and exported from FSRU to shore. Optimum FLNG/FSRU buffer storage volume is the key to maintain gas production/send-out availability when there are LNGC loading/unloading delays.

LNG supplies and sales agreements impact the LNG supply chain and its management. A viable LNG supplies and sales agreement should meet the LNG demand while minimising laytime and its associated costs, such as demurrage or cancelations, as well as minimising loading/unloading congestions at the terminal.

There are seven key performance indicators (KPIs) for a terminal:

1. Loading/unloading availability;

2. Uptime;

3. Downtime;

4. Demurrage;

5. Partial loading/unloading;

6. Cancelled cargoes; and,

7. Terminal congestion.

Loading/unloading availability has been defined in Section 3. Uptime refers to the facility availability where gas production/send-out can be performed. Downtime refers to facility shutdown when gas production/send-out cannot be performed. Demurrage is the period when loading/unloading delays cause LNGCs to remain longer in the terminal than the contractually agreed period to load/unload. Partial loading/unloading is the event when an LNGC can only load/unload part of its LNG parcel due to insufficient volume/storage in an FLNG/FSRU to send/receive the full LNG parcel. Cancelled cargoes are cancelled shipments due to terminal unavailability to receive an LNGC. Terminal congestions occur when LNGCs and other product off-takers (such as condensate and LPG) are at the terminal at the same time due to loading/unloading delays.

A good performing terminal will have high loading/unloading availability and uptime and low downtime, demurrage, partial loading/unloading and it will avoid cancelled cargoes and will reduce its terminal congestion.

The uptime assessment gives indications of expected additional operational costs due to downtime, demurrage, cancelled cargoes and partial loading/unloading.

As an example, one project evaluated by INTECSEA for an LNG import terminal with 250 million SCFD (about 1.9 MTPA) gas send-out capacity, with take-or-pay agreement in place using 10 years of hindcast data, was able to achieve the target 95% uptime by using three days of buffer storage. The results showed, however, that on average that there was one cargo cancellation a year and up to one day of demurrage per offload due terminal unavailability caused by weather. The results also showed that for up to five offloads a year (to avoid cargo cancellations) LNGCs were only able to offload a partial cargo of ∼95% due to insufficient FSRU ullage. These amounted to additional operational costs in the order of US$100 million a year . If quantified as levellised cost of energy (LCOE)—a singular value to represent the indicative cost that, if assigned to every unit of gas produced (per million Btu), will equal to the total Net Present Cost (NPC) of the project—the above under-performance resulted in ∼20%–40% increase in the tariff.

The terminal uptime is evaluated using a combined heuristic, analytical and probabilistic approach. The heuristic assessment is informed by facility operators, LNGC masters and tug/FSRU/FPSO operators experience in offshore loading/unloading and berthing/de-berthing operations. The analytical process includes assessment of metocean conditions, mooring system, maneuverability simulation, model testing, process RAM analysis, human factors in marine operations decision-making and event forecasting methods. Gaps of uncertainties for future predictions are filled by probabilistic Monte Carlo simulations.

There are four main inputs to uptime simulation:

1. Historical hindcast metocean time series transformed to the site location;

2. Mooring analysis;

3. Navigation study; and,

4. LNG supply and sales agreements.

Metocean conditions (wind, wave and current) are the main drivers for LNGC berthing/unberthing operations, loading/unloading operations and gas production/send-out operations. Typically, coastal modeling is required to numerically transform historical hindcast metocean data from a nearby location to the specific project site location.

The objective of mooring assessment is to determine the limiting environmental conditions (wind speed, significant wave height—Hs, wave peak period—Tp, and current speed) for safe mooring, loading/unloading and gas production/send-out operations. The mooring assessment results then provide the basis for mooring, loading/unloading and gas production/send-out operability limits for the uptime assessment. The results of the mooring assessment are benchmarked against side-by-side offloading model test results which INTECSEA has performed and against operators’ experience from offshore side-by-side LNG, LPG and oil offloading and trans-shipments.

The objective of a navigation study is to determine the limiting environmental conditions (wind speed, significant wave height—Hs and current speed) for safe tug operations. This includes escorting LNGCs in the channel to and from the berth pocket and assisting LNGCs in maneuvering to berth and de-berth. The navigation study is typically based on past project experience, tug master input, results and conclusions from the Safe Tug Joint Industry Project (Marin, 2007–08) and the site specific berthing simulation performed. The limiting environmental conditions also depend on the number and type of tugs used.

Typical or expected LNG supplies and sales agreement conditions are used to model the operational philosophy of the terminal. This includes conditions that define laytime, demurrage, laydays, laycan, sales agreements, minimum availability and throughput and partial loading/unloading.

The terminal model (storage size and configuration) along with its associated operability limits and operational philosophy are then taken to the time domain simulation through the transformed historical hindcast metocean time series to simulate the terminal techno-commercial performance through the time series. The statistical results of the KPIs mentioned in Section 4 are then derived to assess the viability of the terminal.

INTECSEA has been applying this process to assess the techno-commercial viability in more than 23 LNG export terminals (FLNGs) and LNG import terminals (FSRUs).

INTECSEA has also performed model test on side-by-side offloading to benchmark the analysis results as well as taking into account the operators’ experience in offshore side-by-side LNG, LPG and crude oil offloading. For side-by-side berthing/de-berthing operations, the berthing simulation results are also benchmarked against JIP results on safe tug operations (which include model test and real world test), as well as taking into account tug and LNGC master input, full mission and desktop bridge simulations.

The past projects’ outcomes highlighted the importance of uptime simulation in aiding owner(s) and/or operator(s) in better decision-making for the project’s direction. Some of the following benefits of uptime assessment have been realised:

1. Decisions to discard or optimise breakwaters to reduce CAPEX.

2. Decisions to discard of select terminal locations based on commercially achievable performance.

3. Selection of possible terminal mooring systems; thereby allowing operators and/or owners to select the best terminal configuration for optimum commercial performance.

4. Offloading configuration selection for metocean conditions at the terminal location (i.e. side-by-side or tandem offloading).

5. Viability of pre-investment for terminal expansion.

6. Optimised buffer storage volume to meet logistics requirements.

7. Allowing owners and/or operators to minimise/mitigate potential operational risks shown by uptime assessment in the terminal agreements.

8. Key input to LNG supply and sale contracts.

9. Forecasting operational costs for more accurate tariff calculations.

10. Determining the best period for inspection/maintenance and associated equipment reliability requirements.

The uptime assessment, which has been developed and used by INTECSEA in the past six years for the purpose of assessing project-integrated LNG offloading availability for FLNG, is the key to terminal performance guarantees for LNG or natural gas off-takers and suppliers.

The uptime assessment is used to forecast the techno-commercial performance of offshore LNG terminals, allowing owners and/or operators to gain confidence on achievable LNG throughput, the best for facility configuration, storage size, offloading equipment and location and CAPEX and OPEX.

Recent project experience has also shown that an uptime assessment carried out during the early stages of the project development can assist in commercial and technology selections.