An export terminal is designed around the gas it will receive, and that gas is not a choice. It is whatever the reservoir produces, and it dictates a surprising amount of what the plant looks like.
Where it comes from
Non-associated gas comes from a field produced for gas alone. Output can be turned up or down to match the plant, which is what a liquefaction project wants: steady, controllable feed against a fixed schedule of cargoes.
Associated gas is produced with crude oil, and its rate follows oil production rather than gas demand. Historically much of it was flared for want of anywhere to send it, and a meaningful share of LNG capacity exists to monetise gas that would otherwise be burned at the wellhead. It is a harder feed to build against, because the operator controls the oil and the gas arrives as a consequence.
Coal seam gas is a special case that shaped an entire export region. It is almost pure methane, very lean, with little carbon dioxide and few heavier hydrocarbons — so the treatment section is small and there are almost no liquids to sell. What it costs instead is thousands of shallow wells across a large area and a gathering network to match, because each well produces very little.
Shale gas varies more than any other source, from dry and lean to very rich, and a plant fed from a pipeline grid rather than a dedicated field takes whatever the grid delivers within specification.
What is in it
Methane, mostly: anywhere from about 70 to 98 per cent. Then a list of things that all have to go.
Ethane, propane, butane and heavier. Valuable, and also dangerous in the cold section because they freeze. They are removed and sold as natural gas liquids, which at a rich-feed plant is a serious revenue line rather than a by-product.
Water. Freezes. Must reach roughly a tenth of a part per million.
Carbon dioxide. Freezes solid at around minus 78 degrees, well above cargo temperature, and would block the main exchanger. Must reach single-digit parts per million.
Hydrogen sulphide. Toxic, corrosive, and subject to strict product specification.
Nitrogen. Does not freeze, but does not liquefy readily either. It dilutes the heating value, accumulates in the vapour space, and contributes to stratification in storage. Specifications typically hold it near one per cent, so it is rejected during processing.
Mercury. Present in traces, and it attacks aluminium — which is what the main cryogenic heat exchanger is made of. A few micrograms per cubic metre is enough to matter over years.
Helium. Occasionally present in commercial quantity, and worth extracting where it is, because helium has few sources and a high price.
Why two identical plants look different
Nameplate capacity says how much LNG a plant makes. It says nothing about how much of the site is refrigeration.
A plant on lean, sweet coal seam gas needs modest treatment: dehydration, a small carbon dioxide removal unit, mercury guard beds, and it is nearly done. A plant on rich, sour offshore gas needs a large amine unit, a full natural gas liquids recovery and fractionation train, sulphur handling, and a great deal more equipment before the gas is ready to chill.
Both might make 5 Mtpa. One is substantially larger, more expensive and more complex than the other, and the difference is entirely upstream of the cold section. This is worth remembering when comparing project costs per tonne: the number reflects the reservoir as much as the engineering.
Feed decline
Reservoirs deplete. A plant built to match early field production can find, a decade or two in, that the field cannot fill its trains.
The consequences show up in the data as an operating plant persistently producing below its nameplate figure, which looks like underperformance and is actually arithmetic. It is one of the reasons nameplate capacity should not be read as output, and one of the reasons some plants pursue new feed sources — a pipeline connection, a neighbouring field, or imported gas — long after they were built.
Where the tracker stops
Global Energy Monitor’s LNG data records terminals, not the fields behind them. A terminal page here shows capacity, status, ownership and location; it does not show the reservoir, its composition or its decline profile, because that is not in the source.
Where the two do meet is the pipeline proximity links, which show gas transmission pipelines passing near a terminal. That is a spatial relationship rather than a supply relationship, and it is labelled as such.